Saltcedar (Tamarix spp.) in the Northern Great Plains: Seed Ecology and
Cultural Considerations
BY
Sarah M. Burnette
A thesis submitted in partial fulfillment of the requirements for the
Master of Science
Major in Biological Sciences
South Dakota State
2012
iii
ACKNOWLEDGEMENTS
This research was funded by the United States Geological Survey’s,
Northern Prairie Wildlife Research Center.
The following individuals or institutions are acknowledged for their
contributions to this research:
Advisory committee Roger Gates, Amy Symstad, Diane Rickerl, and Timothy
Nichols
Valuable information and insight Diane Larson, Wes Newton, Jonathan
Friedman, Patrick Shafroth, and Patricia Johnson
Research Sites United States Forest Service – Rocky Mountain Research
Center (Jack Butler) & Dakota Prairie National Grasslands and Pete Lien and
Son’s Inc.
Statistical analysis Wes Newton and Kenneth Olson
Local saltcedar insight Ron Moehring and Scott Guffey
The author would also like to acknowledge the administrative personnel and staff
at the West River Agricultural Center for their helpfulness and support.
Additionally, the field technicians that aided in data collection are acknowledged:
iv
Adrianne Shabi, Josh Peterson, Amber, Josh, Chris Misar, Amber Ressett, Josh
Lee, Nichole Phelps, and Alissa Fendrick.
v
Abstract
Saltcedar (Tamarix spp.) in the Northern Great Plains: Seed Ecology and
Cultural Considerations
Sarah M. Burnette
2012
Saltcedar (Tamarix spp.) is becoming more commonplace within riparian
habitats of the Northern Great Plains (NGP) and has been given “noxious weed”
status in many of the states in this region. Little information on the environmental
conditions conducive to the establishment of saltcedar specific to this region
exists, however. In addition to biological implications, there is little to no
understanding as to the sociological impacts of a saltcedar invasion. Therefore,
three separate studies were conducted to 1) evaluate saltcedar seed ecology
dynamics in a controlled growing chamber setting, 2) assess the seasonality of
saltcedar seedlings in the northern Great Plains (NGP), and 3) to determine
native Lakota cultural viewpoints of saltcedar and its impacts on the tribes in
South Dakota.
The first study evaluated saltcedar seedling emergence in conditions
found in riparian habitats of the Great Plains. Growth chamber experiments
evaluated the effects of soil moisture, soil sterilization, and vegetation cover on
saltcedar seedling emergence in two soil types (clayey and sandy) and with seed
vi
from two locations in western South Dakota. Emergence increased with
increasing soil moisture and was consistently higher in clayey than in sandy soils.
Soil sterilization and grass cover decreased seedling emergence, and
emergence differed between seed sources.
In the second study, seasonality of saltcedar (Tamarix spp.) seedling
emergence was monitored in two sites in western South Dakota as related to soil
moisture, light availability, and distance from seed source. In June 2011, a total
of 120 plots were established in each of three moisture levels (40 plots per level)
at each site. Moisture levels were categorized as: 1) wettest, 2) moderate, and
3) driest and were determined based upon topography (slight differences in
elevation), distance from nearest standing water and/or the presence of wetlandobligate vegetation at the time of plot establishment. Light availability and
distance to the nearest seed source were measured at each plot. The moderate
moisture level had the highest number of newly emerged seedlings at the
beginning of seedling emergence (mid-July) at both sites, but after that, there
was little or no difference in seedling emergence among the moisture levels.
Seedling mortality was high; in general 54% of seedlings died within 2 weeks of
emerging and only 31% of total emergents remained at the end of the growing
season (end of September). Seedling survival was highest in the moderate
moisture level (p ≤0.06). Seedling emergence and survival were significantly
related to light availability at both sites (p ≤0.06), but to distance from seed
vii
source at only one site. However, seedling emergence and survival were not
strongly related to either of these factors at either site (all r ≤ 0.39).
Ecological effects of saltcedar are widely investigated; little attention is
given to cultural considerations. Invasive species can and do affect social and
cultural systems in a myriad of ways, usually culturally specific. Therefore, the
goal of the final study, through the avenue of interviews, was to gain
understanding of the current and possible effects and concerns of saltcedar on
the Lakota culture. Interviewed participants were members of a South Dakota
federally recognized tribe and/or residents of a South Dakota, Lakota reservation.
A priority was to obtain feedback from various internal groups and subgroups.
These groups are defined as: 1) ranchers, a) land owners, b) land leasers; 2)
traditional practitioners (This included but was not limited to those who regularly
participate in cultural and spiritual practices, speak their native language, etc…)
and; 3) resource managers, a) park and recreation, b) tribal land officials. Three
participants were purposely selected to represent each sub-category, giving a
total of 15 interviewees. Three main themes were highlighted from the
participant’s responses, stressing concern for 1) culturally significant vegetation,
2) ranching endeavors, and 3) land management time and resources.
Emphasizing these concerns can significantly contribute to education about
saltcedar and management efforts. An understanding of how saltcedar
infestations affect the Lakota culture enhances efforts at environmental and
cultural conservation.
viii
TABLE OF CONTENTS
Abstract………………………………………….………………………………………iii
List of Tables…………………………………………….……………………………..viii
List of Figures…………………………………………….……………………………..ix
List of Appendix Figures and Documents…………………………………………....xi
Chapter 1. Literature Review………………………………..…………………………1
Seed Ecology……………………………………………..……………………..4
Cultural Review……….……………………………..…………………………..6
Chapter 2. Evaluating Saltcedar Seedling Emergence in a Controlled
Environment…………………………………………………………………………..…9
Abstract…………………...……….……………………………………………..9
Introduction……………………………..………………………………………10
Materials and Methods…………………………………………………………12
Results…………………………………….……………………………………15
Discussion……………………………..……………………………………….16
Literature Cited……………………..…………………………………………19
Tables…………………………………………………………………………...24
Figures………………………………………………………………………….27
Chapter 3. Saltcedar in the Northern Great Plains: Evaluation of
Seasonality……………………………………………………………………...……...30
Abstract…………………………………………………………………………30
Introduction………………….………………………………………………….31
ix
Materials and Methods………….…………………………………………….33
Results….………………………………………………………………………37
Discussion…..………………………………………………………………….39
Literature Cited………………….……………………………………………..44
Tables…………………………………………………………………………...47
Figures………………………………………………………………………….50
Chapter 4. Saltcedar in the Northern Great Plains: Cultural
Considerations…………………………………………………………………………58
Abstract………..………………………………………………………………..58
Introduction….………………….………………………………………………59
Materials and Methods………………………………………………………..61
Results………………………………………………………………………….64
Discussion………………………………………………………………………67
Literature Cited…………………………………………………………………69
Tables…………………………………………………………………………..71
Figures………………………………………………………………………….73
Thesis Conclusions……………...…………………………………………………….74
Appendix A……………………………………………………………………………..76
Appendix B……………………………………………………………………………..78
Appendix C……………………………………………………………………………..80
Appendix D……………………………………………………………………………..86
x
LIST OF TABLES
Chapter 2
Table 1.
ANOVA results for effects of soil type, seed source, moisture level,
and their interactions on percent emergence of saltcedar….……..24
Table 2.
ANOVA for assessing effects of soil type, seed source, soil
sterilization, and their interactions on percent emergence of
saltcedar…………………………………………..…………..………..25
Table 3.
ANOVA for assessing effects of soil type, seed source, vegetation
cover/bare ground, and their interactions on percent emergence of
saltcedar…………………………………….………………………….26
Table 3.1
Least-squares means (LSMEANS) for ANOVA significant effects in
Table 3………………………………………………………………….26
Chapter 3
Table 1.
ANOVA results for number of emerged seedlings and number of
surviving seedlings at Wasta Site. Moderately significant effects
are in italics and highly significant effects in bold…………….…..47
Table 2.
ANOVA results for number of emerged seedlings and number of
surviving seedlings at USFS Site. Moderately significant effects are
in italics and highly significant effects in bold……………………..48
Table 3.
Simple regression of total number of emerged seedlings (over the
growing season) and number of alive seedlings at the final
sampling period (period 5) on light availability……………….……49
Table 3.1
Simple regressions of total number of emerged seedlings (over the
growing season) and number of alive seedlings at the final
sampling period (period 5) on distance from seed source……….49
Chapter 4
Table 1.
Responses to the question “What are your experiences with
saltcedar on the reservation?”………………………………………..76
xi
Table 2.
Responses to the question “How do you think or feel saltcedar is
currently impacting the reservation?”………………………………76
Table 3.
Responses to the question “Do you have any concerns about the
spread of saltcedar on the reservation, if so what are your concerns
and why they are important?”………………………..……………….71
Table 4.
Responses to the question “Would more saltcedar on the
reservation impact your life? How so?”……………………..………72
LIST OF FIGURES
Chapter 2
Figure 1.
Least square means of seed source germination test results for
seed collected in early July, 2010 and mid-September,
2010…………………………………...………………………..………27
Figure 2.
Least squares means of number of emerged seedlings (out of 100)
for each moisture level in two different soil types; SE = 1.67……28
Figure 3.
Least squares means (SE = 1.69) of saltcedar emergence in bare
ground and in established smooth brome and inland
saltgrass…………………………………………………………….….29
Chapter 3
Figure 1.
Picture of marked saltcedar seedlings at USFS Site taken on
August 24th, 2011………………………………..…………………….57
Figure 2.
Least squares means of total number of newly emerged seedlings
at Wasta Site from each moisture category (1= wettest, 2=
moderate, 3= driest) at each sampling period. Letters above bars
indicate significant (p <0.10) differences between means across the
whole figure………………………………………………..……..……50
Figure 3.
Least squares means of total number of newly emerged seedlings
at USFS Site from each moisture category (1= wettest, 2=
moderate, 3= driest) at each sampling period. Letters above bars
xii
indicate significant (p <0.10) differences between means across the
whole figure………….………………………………….…...…..…….51
Figure 4.
Least squares means of total number of surviving seedlings at
Wasta Site from each moisture category (1= wettest, 2= moderate,
3= driest) at each sampling period. Lowercase letters
above bars indicate significant (p <0.10) differences between
means within moisture level, and uppercase letters indicate
significant differences within sampling period……………………..52
Figure 5.
Least squares means of total number of surviving seedlings at
USFS Site from each moisture category (1= wettest, 2= moderate,
3= driest) at each sampling period. Lowercase letters above bars
indicate significant (p <0.10) differences between means within
moisture level, and uppercase letters indicate significant differences
within sampling period………………...………………………………53
Figure 6.
Scatterplot of total seedling emergence at USFS Site from each
moisture level in relation to distance (cm) from nearest seed
source…………………………………………………………...……...54
Figure 6.1
Scatterplot of number of surviving seedlings at the end of the
growing season at USFS Site in relation to distance (cm) from
nearest seed source…………………………………………………..55
Figure 7.
Scatterplot of number of surviving seedlings at Wasta Site at the
end of the growing season in relation to distance from seed source
(cm)……………………………………………………………………...56
Figure 8.
Scatterplot demonstrating the relationship between light availability
and distance from seed source at both sites. Reference A is Wasta
Site and reference B is USFS Site…………………………...……...58
Chapter 4
Figure 1.
Map of South Dakota Native American reservations highlighted in
pink and major waterways lined in blue (nationalatlas.gov)………73
xiii
LIST OF APPENDIX FIGURES AND DOCUMENTS
Appendix A
Figure 1.
Picture of smooth brome grown in clayey soil used for Chapter 2’s
vegetation cover test…………………………………………………..76
Figure 2.
Picture of inland saltgrass grown in sandy soil used for Chapter 2’s
vegetation cover test…………………………………………………..77
Appendix B
Figure 1.
Picture of a level 1 plot located at Wasta Site. Shows a layer of
organic material left on the plot once water receded. The lone
saltcedar seedling was the only seedling documented having grown
on the organic layer……………………………………………………78
Figure 2.
Picture of saltcedar seeds at peak maturity at Wasta Site.
Photograph was taken on July 7th, 2011…………………..………..79
Figure 3.
Scatterplot of total emergence at Wasta Site in relation to light
availability………………………………...…………………………….80
Figure 4.
Scatterplot of total emergence at USFS Site in relation to light
availability………………………………………………………………80
Figure 5.
Scatterplot of seedlings alive at sampling period 5 at Wasta Site in
relation to light availability……………....……………………………81
Figure 6.
Scatterplot of seedlings alive at sampling period 5 at USFS Site in
relation to light availability…………………..………….…………….81
Appendix C
Doc. 1.
Interview Introduction………………………………………………….80
Doc. 2.
Participant's Agreement……………………………………………….81
Doc. 3.
Saltcedar Impacts Questionnaire…………………………………….83
Figure 1.
Visual Aid……………………………………...………………………..85
Figure 1.1
Visual Aid………………………………………………………….……86
xiv
Appendix D
Doc. 1.
Disposal Documentation……………………………….……………..87
2
CHAPTER 1
Literature Review
Saltcedar (Tamarix spp.) species originated from the southern
Europe/eastern Mediterranean region (Di Tomaso 1998). Ten species were
introduced to the United States by the early 1800’s and have since been used for
landscaping, erosion control, and windbreaks (Brotherson and Winkel 1986).
Once introduced, Tamarix did not take long to escape into the wild. As early as
1920 the tree was considered a pest species in southwestern states (Botherson
and Winkel 1986; ISSG; Pearce 2007).
Saltcedar is a small tree or shrub with slender branches. The leaves
alternate and are small, subulate and mostly sessile. The leaves have
multicellular, external glands which excrete salt. The flowers are small, solitary
or often in scaly-bracteate racemes, spikes or panicles. Sepals (4-5) are distinct
or less often connate below, imbricate, and persistent; petals alternate with the
sepals and are white, pink or red with stamens on a fleshy nectary-disk.
Stamens are as many or 2x as many as petals. Bark is glabrous and will vary
with species from deep brown, to purple, to red. The fruit is a loculicidal capsule
with the seeds erect, terminating in a single tuft of hairs. The tree is mostly
halophytic or xerophytic and can be either monoecious or dioecious (McGregor
et al, 1986).
Tamarix is in the family Tamaricaceae, which is represented by 54 species
worldwide (Baum 1967). It is believed that five Tamarix species grow in the wild
3
in the United States: T. parviflora (once known as T. tetrandra Pall.), T.
ramosissima (also known as T. pentandra), T. chinensis, T. aphylla, and T.
gallica (Di Tomaso 1998). Young et al. (2004) suggest that T. chinensis and T.
ramosissima are the correct taxa for the widespread saltcedar found in North
America. These two species are extremely difficult to distinguish from each other
and can be mistaken for being the same species (Di Tomaso 1998). Common
names for the species are tamarisk, salt cedar or saltcedar; for the purpose of
this study, the name saltcedar will be used.
Impacts caused by saltcedar stands range from changing patterns in
flooding and erosion throughout riparian systems to an increase in fire frequency
(Di Tomaso 1998; Young et al. 2004). Saltcedar also can cause significant
changes in flora and fauna diversity (Di Tomaso 1998). In Afron Canyon near
Barstow, CA, 70% of the native vegetation was replaced by saltcedar with an
infestation that began in the 1960’s (deGouvenain 1996). In the lower Colorado
River, saltcedar replaced nearly 90% of the native riparian vegetation historically
dominated by cottonwood-willow trees (Crins 1989). Additional impacts include
changes in ground water availability and soil chemistry (Young el al. 2004).
In 1987, saltcedar infestations in the southwestern region of the United
States were estimated to exceed 600,000 ha (Brotherson and Field 1987) with an
increase rate of 3-4% per year (Di Tomaso 1998). Along the Colorado and
Green Rivers, the incursion of saltcedar was calculated at 20 km of river length
per year (Graf 1978; Di Tomaso 1998). Saltcedar’s startling invasion in the early
4
1900’s through the 1940’s has been attributed to alteration of hydrological
regimes caused by construction of large dams during this period (Brock 1994; Di
Tomaso 1998; Pearce 2007).
The early stages of the invasion began in the southwestern states.
However, during this time Tamarix taxa, particularly T. ramosissima and T.
chinensis, had spread throughout the western states, including the northern
Great Plains (Wyoming, Montana, North Dakota, South Dakota and Nebraska)
(Pearce 2007). Spread northward from southern states, yard and erosion control
plantings, and accidental introductions, are believed to account for the multiple
sites of saltcedar invasion throughout the Great Plains (Pearce 2007). In this
region, saltcedar is concentrated in floodplains and reservoir shores, where the
tree’s roots can reach the water table (Everitt 1980; Pearce 2007). It was
originally believed that saltcedar would not spread from the southwestern states
because it was not adapted to cooler temperatures in the north (Baum 1978;
Brock 1994). However, the most common species in the western United States,
T. chinensis and T. ramosissima, originated in the cooler, drier climates of
Mongolia, northern China, Tibet, Afghanistan, Iran, Iraq, Turkmenistan,
Kazakhstan, and Turkey (Pearce 2007).
Agriculture is South Dakota’s primary use of its land base, with 17,684,800
ha in use for all of the state’s operations (USDA). Much of this land base is
undeveloped rangeland, which includes an extensive riparian network. Saltcedar
is considered a serious threat throughout South Dakota rangeland. South
5
Dakota and tribes therein have launched eradication efforts throughout many of
their riparian habitats. However, state officials within the agricultural and
horticultural professions have questions regarding environmental conditions that
influence the emergence and growth of saltcedar in South Dakota (R. Moehring,
South Dakota state weed and pest supervisor, pers. comm., October 2009).
Seed Ecology. Saltcedar is a facultative phreatophyte; seeds need moisture to
germinate, but once established, saltcedar is able to survive by absorbing water
directly from the water table or other permanent ground supply. Saltcedar trees
produce seeds throughout the entire growing season, having one major and one
minor peak of production (Di Tomaso 1998).
Due to the high number of acres infested and impacted by saltcedar in the
southwestern United States, extensive research and control efforts have been
implemented throughout this region. Research completed in the southwest
region holds value for the overall characteristics and growth trends of saltcedar.
However, the data are specific to that region of study. Soil characteristics,
species composition, and climate are a few of the characteristics that vary among
regions of the United States and that could influence saltcedar ecology.
Despite the large amount of saltcedar research done in the southwestern
United States and elsewhere, little is known about the ecology of saltcedar
seeds. Young et al. (2004) state two reasons for the inattention to seed ecology.
First, the small size of the seeds [saltcedar seeds measure 0.17 mm in diameter
and 0.45 mm in length (Baum 1978)] makes it challenging to collect and count
6
(Young et al. 2004). Second, seeds have a very short shelf-life. Once mature,
saltcedar seeds only remain viable for approximately 5 weeks under normal
conditions (Di Tomaso 1998; Young el al. 2004); thus, any research involving
seeds must be performed as soon as seeds mature (Young et al. 2004).
Saltcedar is most prevalent in semi-saturated soils in the southwest
(Nagler et al. 2011; Di Tomaso 1998), but it is unclear what moisture conditions
are needed for establishment in the NGP.
Arbuscular mycorrhizal fungi (AMF) are one type of soil biota that often
have positive effects on plant emergence and/or growth (Meinhardt et al. 2012;
Beauchamp et al. 2005). Studies in the southwestern United States showed little
to no AMF colonization of saltcedar roots in the field and no effect of
experimental inoculation with AMF on saltcedar root growth (Titus et al. 2002;
Beauchamp et al. 2005), but saltcedar-soil biota relationships have not been
investigated in the northern Great Plains. Additionally, numerous studies have
shown that saltcedar establishment is hindered by established vegetation
compared in areas with exposed soil (Sher et al. 2000, 2002; Stromberg 1997);
however the emergence phase of establishment in relation to other species near
or just beyond their seedling stage has yet to be studied.
The Missouri River Watershed Coalition is a collaboration between
Montana, North Dakota, South Dakota, Wyoming, Nebraska and Colorado
departments of agriculture to coordinate the management of invasive plant
species within the six-state area. In a 2008 meeting of the coalition, concerns
7
about the spread of saltcedar into the Great Plains region generated questions
about factors that affect saltcedar establishment in the region and ecosystems
covered by this coalition (R. Moehring, South Dakota Weed and Pest Supervisor,
pers. comm. 2009). Recognizing that the optimum management approach for
controlling saltcedar is to prevent its establishment (Ohrtman et al. 2011), the
coalition expressed the need for information about the seed and seedling stage
of saltcedar in the NGP. Basic information about the timing of seed set, seedling
emergence, seedling survival, and seed longevity in the field, as well as
identifying local ecological conditions that favor or hinder establishment is critical.
Therefore, the first segment of this research investigates (1) tests the
effects of soil biota, competition from other vegetation, and soil moisture on
saltcedar emergence in controlled growth chamber experiements, (2) determines
seed viability after outdoor winter storage in NGP conditions and 3) measures
seasonality of saltcedar emergence in two infested areas of western South
Dakota as related to soil moisture and light availability.
Cultural Considerations. Within South Dakota’s boundaries are nine Native
American Reservations of Lakota, Nakota, and Dakota peoples. These
reservations and their tribal members depend upon the land for individual and
family ranching endeavors, revenue generated from leasing their lands, and
various flora and fauna cultural needs, among other things.
The 2007 agricultural census reports approximately 3,678,300 ha of tribal
land in use for agricultural production throughout all nine reservations, with
8
1,544,187 ha operated by tribal members (McCurry 2010). The reservations
depend upon the riparian networks to maintain this agricultural production.
Even with the widely researched adverse effects of introduced species on
the physical environment, little research has taken place as to their effect on
social systems (Pfeiffer and Voeks 2008). Native flora are a significant factor in
the cultural identity of indigenous societies throughout the world (Stepp et al.
2002). Semi-domesticated and domesticated species have been utilized, tended
to, and conserved by native peoples for millennia, which has resulted in
individual, unique cultural societies (Pfeiffer and Voeks 2008).
Invasive species have the potential to deprive communities of the
biodiversity necessary to maintain cultural resilience. Culturally significant
natural resources may decline in abundance or have restricted access as a result
of an establishment of invasive species (Pfeiffer and Voeks 2008). For example,
basket weavers from California were impacted when increasing populations of
starthistle (Centaurea solstitialis), scotch broom (Cytisus scoparius), and stinging
nettle (Urtica gracilis) within their ancestral gathering groves displaced redbud
(Cercis canadensis) and deergrass (Muhlenbergia rigens), which are traditional
weaving materials (Pfeiffer and Ortiz 2007). Through water deprivation and
habitat encroachment, saltcedar has significantly decreased the populations of
culturally significant vegetation such as cottonwood (Populus fremontii), willow
(Salix exigua, S. lasiandra), sandreed (Calamovilfa gigantea) and yucca (Yucca
spp.) in the southwest. The Hopi tribe has been forced to uproot and replant
9
these species closer to their reservation for use and preservation (Pfeiffer and
Voeks 2008).
Displacement of culturally significant native species by invasive species
can create a ripple effect by also displacing traditions that are tied to the native
species (Pretty 2002). Local natural resources define cultural identity through
folk taxonomies, ethnobiological practices, songs, and oral stories (Pfeiffer and
Voeks 2008). Languages live within the names of flora, fauna, and other natural
resources through their definitions; it is common for the name of a plant or place
to be a description of what it looks like or how it is used. Thus, when native
species decline, community members face challenges in maintaining or reviving
their cultural traditions.
Chemically treating invasive species has caused an indirect effect on
culturally significant vegetation and, therefore, the cultural societies themselves
(Mackenzie 2003). Pesticide drift onto native vegetation used in basket weaving
has been documented to stunt growth and deform the plants, making them
unusable (Pfeiffer and Voeks 2008).
Therefore, the goal of the second portion of this project is to increase
understanding of Native American, specifically Lakota, cultural perspectives of
and impacts felt from invasive saltcedar. A series of interviews were conducted
with members of Lakota tribes or with those that reside on a Lakota reservation
in South Dakota.
Literature cited in this chapter can be found after chapter’s 1, 2, or 3.
10
CHAPTER 2
Evaluating Saltcedar Seedling Emergence in a Controlled Environment
Abstract
Saltcedar (Tamarix spp.) is becoming more commonplace within riparian habitats
of the Northern Great Plains (NGP) and has been given “noxious weed” status in
many of the states in this region. Little information on the environmental
conditions conducive to the establishment of saltcedar specific to this region
exists, however. Therefore, this study evaluated saltcedar seedling emergence
in conditions found in riparian habitats of the NGP. Growth chamber experiments
evaluated the effects of soil moisture, soil sterilization, and vegetation cover on
saltcedar seedling emergence in two soil types (clayey and sandy) and with seed
from two locations in western South Dakota. Emergence increased with
increasing soil moisture and was consistently higher in clayey than in sandy soils.
Soil sterilization and grass cover decreased seedling emergence, and
emergence differed between seed sources. Understanding factors that affect
saltcedar emergence and establishment from seed can assist land managers in
identifying sites with conditions that might encourage or inhibit saltcedar
emergence. Clayey, moist soils with sparse vegetation, and a healthy population
of microbes present the highest risk for saltcedar emergence in the Northern
Great Plains.
Nomenclature: saltcedar, Tamarix ramosissima Ledeb., Tamarix chinensis
Lour., and Tamarix hybrids.
11
Key words: Northern Great Plains, grassland, seed ecology, riparian, seedling,
emergence, germination
Introduction
Saltcedar’s startling invasion began in the early 1900’s in the
southwestern United States and has been attributed to alteration of hydrological
regimes caused by construction of large dams during this period (Brock 1994; Di
Tomaso 1998; Pearce and Smith 2007). In 1987, saltcedar (Tamarix spp.)
infestations in the southwestern United States were estimated to exceed 600,000
ha (Brotherson and Field 1987) with an increase rate of 3-4% per year (Di
Tomaso 1998). Currently, saltcedar dominates many floodplain ecosystems in
this region (Birken et al. 2006; Brock 1994; Friedman et al. 2008) and it is the
third most frequently occurring woody species along rivers of the western United
States (Nagler et al. 2011). This species displaces native vegetation (Birken et
al. 2006), reduces plant species diversity (Di Tomaso 1998; Glenn and Nagler
2005), and changes riparian flooding and erosion patterns (Di Tomaso 1998;
Young et al. 2004).
Although saltcedar invasion was evident in the southwestern United
States as early as 1930 (Nagler et al. 2011), it was not until the 1950’s and
1960’s that saltcedar was discovered in the Northern Great Plains (NGP) region
(Wyoming, Montana, North Dakota, South Dakota and Nebraska); (Pearce and
Smith 2007). In this region, saltcedar is concentrated in floodplains and reservoir
12
shores, where the tree’s roots can reach the water table (Everitt 1980; Pearce
and Smith 2007).
Due to the severity of saltcedar in the southwestern United States,
extensive research and control efforts have been implemented throughout this
region (Nagler et al. 2011). Research completed in the southwest holds value for
the overall characteristics and growth trends of saltcedar. However, data are
specific to that region. Soil characteristics, species composition, and climate
vary among regions of the United States and could influence saltcedar ecology.
Though saltcedar is listed as a noxious weed in North and South Dakota
(National Resources Conservation Service, 2012), saltcedar’s presence in the
NGP (with the exception of Montana) is sparse when compared to the southwest
region (Nagler et al. 2011). However, saltcedar persistence in the NGP is
increasing and has been attributed to climate warming and genetic changes
(Friedman et al. 2008; Pearce and Smith 2007; Ohrtman et al. 2011). Large
stands of saltcedar exist in this region.
Despite the large amount of saltcedar research done in the southwestern
United States and elsewhere, little is known about the ecology of saltcedar
seeds. Two reasons contribute to this inattention to seed ecology. First, the
small size of the seeds [saltcedar seeds measure 0.17 mm in diameter and 0.45
mm in length (Baum 1978)] makes it challenging to collect and count (Young et
al. 2004). Second, the seeds have a very short shelf-life. Once mature,
saltcedar seeds only remain viable for approximately 5 weeks under normal
13
conditions (Di Tomaso 1998; Young el al. 2004). Therefore, any research
involving seeds must be performed as soon as seeds mature (Young et al.
2004).
Saltcedar is most prevalent in semi-saturated soils in the southwest
(Nagler et al. 2011; Di Tomaso 1998), but it is unclear what moisture conditions
are needed for establishment in the NGP. Arbuscular mycorrhizal fungi (AMF)
are one type of soil biota that often have positive effects on plant emergence
and/or growth (Meinhardt et al. 2012; Beauchamp et al. 2005). Rickerl et al.
(1994) found that AMF infection varies within a species dependent upon soil
moisture. Studies in the southwestern United States showed little to no AMF
colonization of saltcedar roots in the field and no effect of experimental
inoculation with AMF on saltcedar root growth (Titus et al. 2002; Beauchamp et
al. 2005), but saltcedar-soil biota relationships have not been investigated in the
northern Great Plains.
Additionally, numerous studies have shown that
saltcedar establishment is hindered by established vegetation compared to areas
with exposed soil (Sher et al. 2000, 2002; Stromberg 1997); however the
emergence phase of establishment in relation to other species near or just
beyond their seedling stage has yet to be studied.
Preventing establishment is the optimal management strategy for
saltcedar or any invasive species (Ohrtman et al. 2011). New infestations begin
when seeds arrive at a location, emerge, and become established individuals.
14
Therefore, identifying local ecological conditions that favor or hinder
establishment is critical for saltcedar management in the NGP.
This research tested the effects of three environmental factors – soil
moisture, soil sterilization, and established vegetation – on saltcedar emergence
in highly controlled growth chamber experiments. The overall goal was to collect
quantitative data regarding conditions that would pose a high risk potential for
saltcedar establishment in riparian zones of South Dakota.
Materials and Methods
Seeds were collected at two sites in western South Dakota where
saltcedar trees of varying ages (including mature, seed-producing trees) already
existed: a quarry 3 kilometers east of Wasta, South Dakota (44.083762,
102.398415; Wasta Site) and USDA Forest Service property 64 kilometers
southeast of Rapid City, South Dakota (43.896572º N, 102.679517º E; USFS
Site). Both sites had been quarried for gravel and are adjacent to the Cheyenne
River. Seeds were collected at the first peak of maturity in early July and again
in September during the second peak of seed maturity. Seeds were collected
from at least 5 trees at each site, composited within the site, separated into
batches of 100, and stored at 3° C until being planted for an experiment, which
began within one week of collection. Prior to each emergence test, a random
sample of seeds was tested for viability. For each collection site, 10 replicates of
100 seeds were placed on Whatman number 2 filter paper within a plastic petri
15
dish and then saturated with distilled water. Petri dishes were covered to
maintain moisture and humidity and were maintained at room temperature (~21°
C). Germinated seeds were counted and removed daily for four days.
Clayey and sandy soil, for emergence experiments, was collected from
two local sites. Soil was collected from the surface 7 cm. Soil was sieved (litter
and roots removed), then air dried.
Effects of moisture, soil biota, and vegetative cover on saltcedar
emergence were tested in separate experiments.Each experiment included soil
from each soil collection site and seeds from each seed collection site in a
factorial design, with 5 replicates of each soil x seed-origin combination. Soil
was placed in 27 cm x 27 cm x 5 cm germination flats with drainage holes
stacked in trays without holes. Each flat was seeded with 100 seeds in 5 rows of
20 seeds. Seed origin was randomized for each flat. Seeds were sown on the
soil surface. In each experiment, all flats were subjected to 12 hours of overhead
bulb light at 20°C and 12 hours of darkness at 15°C, established optima for
saltcedar germination (Young et al. 2004). Flats were monitored for emerged
seedlings daily. Seedlings having a radical ≥1 mm long were considered
emerged (Young et al. 2004). Once counted, an emerged seedling was gently
removed.
The first two experiments, examining soil moisture levels or soil biota,
were conducted in early July 2010 with seeds collected during the first seed
16
maturation peak. Seed collected during the second peak of seed maturation
were used in a comparison of vegetative cover in September 2010.
Moisture Level. Moisture levels of 8.2%, 25%, 57% and 85% were established
on a weight by weight basis. Each moisture level was achieved and maintained
by tightly sealing the flat with plastic wrap after adding required water to 2000.0 g
of soil in each flat.
Soil Biota. Each of 5 trays were filled with 2 kg sterilized soil from each soil
collection site, and 5 flats were filled with 2 kg unaltered soil from each collection
site. Sterilized soil was autoclaved for 20 minutes at 121°C and 15 psi at a soil
depth of 3.8 cm. Seeds from each collection site were sown as previously
described. Trays were maintained at 85% moisture, determined to be optimum
in the moisture level experiment.
Vegetative Cover. Saltcedar emergence was tested in three treatments: bare
soil, established inland saltgrass (Distichlis spicata), and established smooth
bromegrass (Bromus inermis). Both smooth bromegrass and inland saltgrass
are prevalent in riparian zones throughout South Dakota. Five flats of each
vegetation treatment x soil type combination were prepared on July 28th, 2010 by
planting enough seeds of the appropriate species to moderately cover the soil in
each flat (nothing in bare soil treatment) and maintained to keep moist in the
growth chambers until the emergence trial began in September. Saltcedar seeds
from each collection site were sown as previously described.
17
Data Analysis. Germination was compared between seed source with a twotailed t-test.
Total number of seedlings emerged was compared among moisture level,
soil biota, and vegetative cover in combination with its soil texture and seed
origin using the mixed model procedure in SAS (SAS Institute 2010).
No emergence was observed at the 8.2% moisture level. This moisture
level was not included in the ANOVA to preserve the stability of the covariance
matrices. An α of 0.05 was used to determine significance.
Results
Seed from USFS Site had higher germination than that of seed from
Wasta Site (p =0.013 and p =0.0014) for the first (p =0.013) and second (p =
0.0014) seed maturation peak (Figure 1). Emergence was 4-6 percentage units
lower for seeds from Wasta Site than from USFS Site. No interactions involving
seed source were detected (Tables 1-3).
Soil Moisture. Emergence differed between soil types and generally among
moisture levels (Table 1). Higher soil moisture yielded higher emergence.
Moisture level interacted with soil type (Table 1). In the sandy soil, emergence
plateaued above the moderate moisture level. Clayey soil yielded consistently
higher emergence than sandy soil (Figure 2).
Soil Biota. Emergence was lower in sterilized soils than in unsterilized soils
(least squares means 14.1 and 21.2 respectively, SE = 1.69). In contrast to the
18
soil moisture test, no effect of soil type or interaction with soil type was observed
(Table 2).
Vegetative Cover. Seedlings emerged in higher numbers in bare soil than
established vegetation (Figure 3). Emergence was similar for the two vegetative
covers. No soil type effect was observed.
Discussion
Higher germination and emergence of saltcedar seeds collected from
USFS Site suggests that viability of seeds produced by different wild populations
of saltcedar in the NGP may vary. Higher viability from seed from the USFS Site
corresponded to a larger population of mature saltcedar trees. More flowering
trees may attract more insects, which seem to be the primary pollination
mechanism for saltcedar (Stevens 1989), enhancing seed viability.
A larger number of mature individuals may contribute greater genetic
variability, that may also lead to higher seed viability (Goggi et al. 2007). Little
information on the pollination biology and genetic variation among saltcedar
populations in the United States is available, however.
In contrast, it is well known that saltcedar seeds require moisture to
germinate (Di Tomaso 1998). However, variation of emergence among different
moisture levels has not previously been quantified. The driest moisture level
(8.2%) tested in this study, in which no seedlings emerged, is fairly typical of
NGP uplands in midsummer (MacNeil et al. 2008, Flanagan and Adkinson 2011,
19
Vermeire et al. 2011), when saltcedar seeds are produced in this region (S.M
Burnette, personal observation). Thus, except in unusually wet years, saltcedar
emergence in the western NGP is unlikely outside of wetter areas adjacent to
riverbanks, stock dams and reservoirs, or in low-lying topography.
In clayey soil, saltcedar emergence may be even higher in moisture levels
exceeding those evaluated. The emergence plateau observed in sandy soils
indicates a maximum emergence level was demonstrated. Greater saltcedar
emergence in the clayey than sandy soil, regardless of soil moisture level, might
be attributed to higher nutrient and water holding abilities of finer-textured soil
(Nagler et al. 2011; Johnson and Koenig 2010). Additionally, saltcedar has a
higher tolerance for soil salinity levels than habitat competitors cottonwood and
willow (Glenn et al. 1998) and clay soils tend to have higher salinity (Nagler et al.
2011). All of these soil characteristics of clayey soil positively influence saltcedar
emergence (Nagler et al. 2011; Glenn et al. 1998).
Lower saltcedar emergence in autoclaved soil may indicate that some
component of the soil biota has a positive influence on saltcedar seed
emergence, since autoclaving soil kills active soil microbial biomass (Cartera et
al. 2007) and alters soil sturcture. Although studies from other locations suggest
that saltcedar does not benefit from AMF (Beauchamp et al. 2005), AMF cannot
necessarily be eliminated as a soil biota component contributing to higher
emergence on sterilized soil. The importance of AMF to saltcedar growth has
been shown to differ among locations (e.g., Anderson et al. 1994). Clearly, the
20
role of soil biota in saltcedar seedling emergence needs further investigation in
the NGP before characteristics of field conditions conducive to saltcedar
emergence can be conclusive.
Absence of established vegetation is one field character favoring saltcedar
seedling establishment (Ohrtman et al. 2011, Sher et al. 2000, 2002; Stromberg
1997), and the results of this study are consistent with previous work. However,
this study demonstrates that even immature, relatively sparse grass cover may
provide some defense against saltcedar by inhibiting emergence. During the
emergence trial, bromegrass was 10 cm in height and inland saltgrass was 4.5
cm.
Each year, individual saltcedar plants produce millions of seeds and, at
least for the two populations in this study, viability of these seeds was quite high
(50-70%). Many of these viable seeds will not emerge to become seedlings,
however, because they do not fall on the proper conditions. Understanding
factors that affect saltcedar emergence and establishment from seed can assist
land managers in identifying sites with conditions that might encourage or inhibit
saltcedar emergence. Clayey, moist soils with sparse vegetation, and a healthy
population of microbes present the highest risk for saltcedar emergence in the
northern Great Plains. Therefore, maintaining dense vegetation cover,
particularly in riparian areas, during the peaks of seed maturation, would be a
reasonable first line of defense against saltcedar invasion (Ohrtman et al. 2011).
21
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Anderson, R. C., B. A. D. Hetrick, and G. W. T. Wilson. 1994. Mycorrhizal
dependence of Andropogon gerardii and Schizachyrium scoparium in two
prairie soils. American Midland Naturalist. 132:366-376.
Baum, B. R. 1978. The genus Tamarix. The Israel Academy of Sciences and
Humanities, Jerusalem, Israel. P. 209.
Beauchamp, V. B., J. C. Stromberg and J. C. Stutz. 2005. Interactions between
Tamarix ramosissima (saltcedar), Populus fremontii (cottonwood), and
mycorrhizal fungi: Effects on seedling growth and plant species
coexistence. Plant and Soil. 275:221–231.
Bhattacharjee, J., J. P. Taylor, L. M. Smith, and D. A. Haukos. 2008. Seedling
competition between native cottonwood and exotic saltcedar: implications
for restoration. Biological Invasions. 11:1777-1787.
Birken, A. S. and D. J. Cooper. 2006. Processes of Tamarix invasion and
floodplain development along the Lower Green River, Utah. Ecol Appl.
16:3:1103-1120
Brock, J. H. 1994. Tamarix spp. (Salt Cedar), and Invasive Exotic Woody Plant
in Arid and Semi-arid Riparian Habitats of Western USA. John Wiley &
Sons Ltd. Ecology and Management of Invasive Riverside Plants. Pages
27-44.
Brotherson, J. D. and V. Winkel. 1986. Habitat relationships of saltcedar
(Tamarix ramosissima) in central Utah. Great Basin Nat. 46:535-541.
22
Cartera, D. O., D. Yellowleesa, and M. Tibbett. 2007. Autoclaving kills soil
microbes yet soil enzymes remain active. Pedobiologia. 51:295–299
Di Tomaso, J. 1998. Impact, biology, and ecology of saltcedar (Tamarix spp.) in
the southwestern United States. Weed Tech. 12:326-336.
Everitt, B. 1980. Ecology of saltcedar- A plea for research. Environ Geo. 3:7784.
Friedman, J. M., J. E. Roelle, J. F. Gaskin, A. E. Pepper, and J. R. Manhart.
2008. Latitudinal variation in cold hardiness in introduced Tamarix and
native Populus. Evol. Appl. 1:598-607.
Glenn, E.P., and P.L. Nagler. 2005. Comparative ecophysiology of Tamarix
ramosissima and native trees in western U.S. riparian zones. Journal of
Arid Environments 61:419-446
Glenn, E.P., R. Tanner, S. Mendez, T. Kehret, D. Moore, J. Garcia, and C.
Valdes. 1998. Growth rates, salt tolerance, and water use characteristics
of native and invasive riparian plants from the delta of the Colorado River,
Mexico. Journal of Arid Environments 40:281-294.
Goggi, A.S., L. Pollak, and J. Golden. 2007. Impact of early seed quality
selection on maize inbreds and hybrids. MAYDICA 52:223-233
Johnson, M. and R. Koenig. Solutions To Soil Problems: III Drainage. Utah
State University: Cooperative Extension
http://extension.usu.edu/files/publications/publication/AG_Soils_200303.pdf Accessed: May 09, 2012.
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Kerpez, T. A. 1997. Saltcedar Control for Wildlife Habitat Improvement in the
Southwestern United States. Washington, DC: USDI. Fish and Wildlife
Service Resource Publication, 169-185.
Meinhardt, K. A. C. A. Gehring. 2012. Disrupting mycorrhizal mutualisms: a
potential mechanism by which exotic tamarisk outcompetes native
cottonwoods. Ecological Applications. 22(2):532-549.
Natural Resources Conservation Service. PLANTS profile, Tamarix ramosissima
Ledeb., saltcedar, U.S. Department of Agriculture.
http://plants.usda.gov/java/profile?symbol=TARA. Accessed: November,
2010.
Nagler, P. L., E. P. Glenn, C. S. Jarnevich, and P. B. Shafroth. 2011.
Distribution and Abundance of Saltcedar and Russian Olive in the
Western United States. Critical Reviews in Plant Science. 30:508-523.
Ohrtman, M. K., S. A. Clay, D. E. Clay, E. M. Mousel, and A.J. Smart. 2011.
Preventing saltcedar (Tamarix spp.) seedling establishment in the
Northern Prairie Pothole Region. Invasive Plant Science and
Management 4:427-436.
Pearce, C. M. and D. G. Smith. 2007. Invasive saltcedar (Tamarix): Its spread
from the American Southwest to the Northern Great Plains. Physical
Geography 28:507-530.
Rickerl D., F. O. Sancho, and S. Ananth. 1994. Vesicular–arbuscular
24
endomycorrhizal colonization of wetland plants. Journal of Environmental
Quality 23(5): 913-916.
Sher, A. A., D. L. Marshall, and J. P. Taylor. 2002. Establishment patterns of
native Populus and Salix in the presence of invasive nonnative Tamarix.
Ecological Applications 12:760-772.
Stevens, L. E. 1989. The status of ecological research on tamarisk
(Tamaricaceae: Tamarix ramosissima) in Arizona. Pages 99-105 in
Kunzmann, M. R., J. R. Roy, and P. Bennett. Tamarisk control in
southwestern United States: Proceedings: National Park Service,
Cooperative National Park Resources Studies Unit, School of Renewable
Natural Resources Special Report No. 9, Tucson, Arizona.
Stromberg, J. C. 1997. Growth and survivorship of Fremont cottonwood,
Goodding willow, and salt cedar seedlings after large floods in central
Arizona. Great Basin Nat. 57:198-208.
Young, J. A., C. D. Clements, and D. Harmon. 2004. Germination of seeds of
Tamarix ramosissima. Journal of Range Management. 57:475-481.
25
Acknowlegements
This project was funded by the U.S. Geological Survey’s Northern Prairie Wildlife
Research Center. Diane Larson, Wes Newton, Jonathan Friedman, Patrick
Shafroth, and Patricia Johnson provided valuable comments on the research
proposal. Wes Newton and Kenneth Olson provided a valuable statistical design
approach. Thanks also to South Dakota State University’s West River Ag Center
personnel and to all the field technicians who assisted in data collection.
26
Table 1. ANOVA results for effects of soil type, seed source, moisture level, and
their interactions on percent emergence of salt cedar.
Effect
Soil Type
Seed Source
Moisture
Soil×Source
Soil×Moisture
Source×Moisture
Soil×Source×Moisture
df
num.
1
1
3
1
3
3
3
df
den. F-value p-value
64
68.41 <0.0001
64
15.56
0.0002
64 107.92 <0.0001
64
0.65
0.4233
64
9.42 <0.0001
64
2.15
0.1029
64
0.67
0.5766
27
Table 2. ANOVA for assessing effects of soil type, seed source, soil sterilization,
and their interactions on percent emergence of salt cedar.
Effect
Soil Type
Seed Source
Soil Type x Seed Source
Test
Soil Type x Test
Seed Source x Test
Soil x Seed x Test
df
df
Fnum. den.
value p-value
1
32
0.32
0.5767
1
32
3.46
0.0722
1
32
0.23
0.6342
1
32
8.67
0.006
1
32
1.73
0.1975
1
32
0
0.9835
1
32
0.04
0.8521
28
Table 3. ANOVA for assessing effects of soil type, seed source, vegetation
cover/bare ground, and their interactions on percent emergence of salt cedar.
Effect
Soil Type
Seed Source
Soil Type x Seed Source
Test
Soil Type x Test
Seed Source x Test
Soil x Seed x Test
df
df
Fpnum. den.
value
value1
1
48
0.88
0.3536
1
48
6.61
0.0133
1
48
0.28
0.06
2
48 11.14
0.0001
2
48
0.1
0.9055
2
48
2.12
0.1311
2
48
0.57
0.5716
Table 3.1. Least-squares means (LSMEANS) for ANOVA significant effects in
Table 3.
Effect
Test
Seed Source
Bare Ground
Brome
Saltgrass
LSMEAN
(SE)
25.9 (1.7)
16.5 (1.7)
15.75 (1.7)
Forest
Service
Wasta
21.9 (1.38)
16.87 (1.38)
29
Figure 1. Least square means of seed germination from two sources collected in
early July, 2010 and mid-September, 2010 in western South Dakota.
80
73.2
70
66.6
60
Germination (%)
51.6
50
48.1
Spring (July)
40
Fall (Sept)
30
20
10
0
Wasta
USFS
30
Figure 2. Least squares means of number of emerged seedlings (out of 100) for
each moisture level in two different soil types; SE = 1.67.
40
a
35
b
Emergence (%)
30
25
c
c
20
c
15
d
10
5
0
0
8.2%
0
25%
57%
clay
85%
8.2%
25%
57%
sandy
85%
31
Figure 3. Least squares means (SE = 1.69) of saltcedar emergence in bare
ground and in established smooth brome and inland saltgrass.
30
a
Emergence (%)
25
20
b
b
15
10
5
0
Bare
Brome
Saltgrass
32
CHAPTER 3
Emergence and Survival of Saltcedar Seedlings in Western South Dakota
Abstract
Saltcedar (Tamarix spp.) is becoming more commonplace within riparian habitats
of the Northern Great Plains (NGP) and has been given “noxious weed” status in
many of the states in this region. Little information on the environmental
conditions conducive to the establishment of saltcedar specific to this region
exists, however. Therefore, seasonality of saltcedar (Tamarix spp.) seedling
emergence was monitored in two sites in western South Dakota as related to soil
moisture, light availability, and distance from seed source. In June 2011, a total
of 120 plots were established in each of three moisture levels (40 plots per level)
at each of two sites. Moisture levels were categorized as: 1) wettest, 2)
moderate, and 3) driest and were determined based upon topography (slight
differences in elevation), distance from nearest standing water and/or the
presence of wetland-obligate vegetation at the time of plot establishment. Light
availability and distance to the nearest seed source were measured at each plot.
The moderate moisture level had the highest number of newly emerged
seedlings at the beginning of seedling emergence (mid-July) at both sites, but
after that, there was little or no difference in seedling emergence among the
moisture levels. Seedling mortality was high; in general 54% of seedlings died
within 2 weeks of emerging and only 31% of total emergence remained at the
end of the growing season (end of September). Seedling survival was highest in
33
the moderate moisture level (p≤0.06). Seedling emergence and survival were
significantly related to light availability at both sites (p≤0.06), but to distance from
seed source at only USFS Site. However, seedling emergence and survival
were not strongly related to either of these factors at either site (all r ≤ 0.39).
Nomenclature: saltcedar, Tamarix ramosissima Ledeb. TARA, Tamarix
chinensis Lour. TACH, and Tamarix hybrids.
Key words: Northern Great Plains, grassland, seed ecology, riparian, seedling,
emergence, germination
Introduction
Saltcedar’s startling invasion began in the early 1900’s through the 1940’s
in the southwestern United States and has been attributed to alteration of
hydrological regimes caused by construction of large dams during this period
(Brock 1994; Di Tomaso 1998; Pearce and Smith 2007). In 1987, saltcedar
(Tamarix spp.) infestations in the southwestern region were estimated to exceed
600,000 ha (Brotherson and Field 1987) with an increase rate of 3-4% per year
(Di Tomaso 1998). Currently, saltcedar dominates many floodplain ecosystems
in this region (Birken et al. 2006; Brock 1994; Friedman et al. 2008) and it is the
third most frequently occurring woody species along rivers of the western United
States (Nagler et al. 2011). Saltcedar displaces native vegetation (Birken et al.
2006), reduces plant species diversity (Di Tomaso 1998; Glenn and Nagler
2005), and changes riparian flooding and erosion patterns (Di Tomaso 1998;
Young et al. 2004).
34
Although saltcedar invasion was evident in the southwestern United
States as early as 1930 (Nagler et al. 2011), it was not until the 1950’s and
1960’s that saltcedar was discovered in the Northern Great Plains (NGP;
Wyoming, Montana, North Dakota, South Dakota and Nebraska) (Pearce and
Smith 2007). In this region, saltcedar is concentrated in floodplains and reservoir
shores, where the tree’s roots can reach the water table (Everitt 1980; Pearce
and Smith 2007).
Due to the high number of acres infested and impacted by saltcedar in the
southwestern United States, extensive research and control efforts have been
implemented throughout this region (Nagler et al. 2011). Research completed in
the southwest region holds value for the overall characteristics and growth trends
of saltcedar. However, the data are specific to that region of study. Soil
characteristics, species composition, and climate are a few of the characteristics
that vary among regions of the United States and could influence saltcedar
ecology. Though saltcedar is listed as a noxious weed in North and South
Dakota (National Resources Conservation Service, 2012), saltcedar’s presence
in the NGP (with the exception of Montana) is sparse when compared to the
Southwest region (Nagler et al. 2011). However, saltcedar persistence in the
NGP is increasing due to climate warming and genetic changes (Friedman et al.
2008; Pearce and Smith 2007; Ohrtman et al. 2011), and isolated large stands of
saltcedar do exist in this region.
35
Despite the large amount of saltcedar research done in the southwestern
United States and elsewhere, little is known about the ecology of saltcedar
seeds. Two factors contribute to this inattention to seed ecology. First, small
seed size [saltcedar seeds measure 0.17 mm in diameter and 0.45 mm in length
(Baum 1978)] makes it challenging to collect and count (Young et al. 2004).
Second, seed viability is brief. Once mature, saltcedar seeds only remain viable
for approximately 5 weeks (Di Tomaso 1998; Young el al. 2004). Therefore, any
research involving seeds must be performed as soon as seeds mature (Young et
al. 2004).
The Missouri River Watershed Coalition is a collaboration between
Montana, North Dakota, South Dakota, Wyoming, Nebraska and Colorado
departments of agriculture to coordinate the management of invasive plant
species within the six-state area. In a 2008 meeting of the coalition, concerns
about the spread of saltcedar into the Northern Great Plains region generated
questions about factors that affect saltcedar establishment and ecosystems in
the region covered by this coalition (R. Moehring, South Dakota Weed and Pest
Supervisor, pers. comm. 2009). Recognizing that the optimum management
approach for controlling saltcedar is to prevent its establishment (Ohrtman et al.
2011), the coalition expressed the need for information about the seedling stage
of saltcedar in the NGP. Basic information about the timing of seed set, seedling
emergence, seedling survival, and seed longevity in the field, as well as
identifying local ecological conditions that favor or hinder establishment is critical.
36
Therefore, this research investigated (1) seed viability after outdoor winter
storage in NGP conditions, and (2) influence of moisture level, light availability,
and distance from seed source on saltcedar emergence in two infested areas of
western South Dakota.
Materials and Methods
Study Sites. Research was conducted at two locations where saltcedar trees of
varying ages (including mature, seed-producing trees) already existed: a quarry 3
kilometers east of Wasta, South Dakota (44.083762 º N, 102.398415 º E; Wasta
Site) and USDA Forest Service property, 64 kilometers southeast of Rapid City,
South Dakota (43.896572º N, 102.679517º E; USFS Site). Both sites are in an
established riverbed and had been quarried for gravel. The nomenclature of
saltcedar believed to be in the study area is T. chinensis and/or a hybrid of T.
chinensis and T. ramosissima (Moehring 2009; Gaskin and Schaal 2003).
Land management agencies had been chemically treating saltcedar at
both study site locations. However, it remains abundant at these two sites
because they were used for attempted biocontrol treatment and consequently
chemical treatment ceased. Tamarisk leaf beetles (Diorhabda elongata) were
released at both sites in 2006, 2007, and 2008, but for undetermined reasons,
establishment never took place. At the USFS Site, chemical treatment of the
southeastern perimeter took place in 2006; therefore, for this research only the
inner region of the stand (where no treatment was applied) was used.
37
Viability of Over-Wintered Seeds. Saltcedar seeds were collected from at least
five trees from each site in October 2010. Seeds were separated from vegetative
parts, mixed by site, and viability tested. For each site, 10 replicates of 100
seeds each were placed on top of filter paper within a plastic petri dish. Filter
paper was saturated with distilled water. Petri dishes were covered to maintain
moisture and humidity and were maintained at room temperature (~21° C).
Seeds were checked for emergence daily for three days; germination of saltcedar
seeds is close to instantaneous once seeds imbibe water (Young 2004; Kerpez
1997). Following this, five 200 seed replicates for each site were randomly
drawn and sealed into 50-micron porosity polyester bags. Seed bags were
secured to the ground in random locations within the saltcedar stand of their
origin on October 5th, 2010. In early May 2011, seed bags were collected and
the seed in each was tested for viability. All bags were recovered except one
from Wasta Site which could not be located.
Seedling Emergence and Survival Monitoring. In June 2010, saltcedar
seedling monitoring plots were established in each of three moisture levels at
each site. Moisture levels were categorized as 1) wettest, 2) moderate, and 3)
driest. Levels were determined based upon elevation above nearest standing
water and/or wetland-obligate vegetation at the time of plot establishment.
Elevation was calculated as height above the nearest standing water or height
above ground level at the edge of nearest obligate vegetation. Moisture level
categories were then defined (1) 0-15 cm, (2) 16-30 cm, and (3) 31-100 cm
38
above edge of standing water or obligate vegetation. In each moisture category,
40 1 x 1m plots were randomly established within each site. The goal was to
span the realistic range of saltcedar habitat encompassing extreme and average
soil moisture availability. High rainfall and subsequent flooding in spring 2011
resulted in seven plots at Wasta Site being submerged at the onset of 2011
emergence monitoring. Consequently, these plots were replaced by seven newly
established plots using the same moisture level criteria described above.
Remaining plots did not require being reassigned to new moisture level
categories. Non-saltcedar vegetation in all plots was clipped to ground level and
maintained at that level throughout the two growing seasons.
Monitoring for emergence began in mid-July, after the first peak of seed
maturation, and continued through late September, ten days after the final fall
seed maturation period, in 2010 and 2011. Monitoring was done biweekly,
yielding five sampling periods. When found, emerged individuals were identified
either as seedlings or rhizome sprouts. Presence of cotyledons differentiated
individuals between seedlings and rhizomes. After identification and counting at
each monitoring time in 2010, emerged seedlings were pulled out. In 2011,
emerged individuals were counted then marked with a plastic ring and an
individual identification marker to monitor for survival (Figure 1). Individuals were
tracked until death or the end of the monitoring period, whichever came first.
Those surviving at the end of monitoring were assumed to have survived the
growing season.
39
Light availability was measured at ground level in each plot in July 2010
with an LP-80 AccuPAR ceptometer (Decagon Inc.). Since vegetation in the
plots was clipped, this light measurement reflects shading from nearby trees.
Distance from the center of each plot to the base of the nearest seed-producing
saltcedar was also measured.
Data analysis. Only data from the second year of monitoring (2011) were
analyzed because of saltcedar seedling identification and regrowth issues in
2010. Light availability measurements were missing for seven plots at Wasta
Site due to equipment problems. Only seedlings (not rhizome sprouts) were
used in statistical analyses.
Generalized linear models (GLM) in a repeated-measures analysis of
variance (ANOVA) framework were used to assess the effects of the three
moisture levels, sampling period, and their interactions on the number of newly
emerged seedlings each sampling period and the number of surviving seedlings
each sampling period. Study plot was considered the replicated whole-unit and
sampling period the repeated measures factor. The association of light and
distance to nearest seed source and any interaction with moisture level on the
response variables were used as potential continuous covariates in the ANOVA.
Since moisture level was the main effect of most interest, only two-way
interactions between moisture level and light or moisture level and distance were
included in the analysis. Mixed linear models procedure (PROC MIXED) of SAS
(SAS Institute 2010) was used to conduct the repeated measures ANOVAs with
40
least squares means and their standard errors reported for significant effects
and/or interactions. An autoregressive lag 1 (AR-1) was assumed for a
variance-covariance structure to account for the repeated measures of sampling
period. Significant effects of light and/or distance, and interactions with moisture
level, if any, were further investigated with simple regressions for the final
sampling period, data which express seedlings that survived the growing period.
P-values <0.10 and <0.05 were considered as moderately and highly significant
respectively. All analyses were done separately for sites A and B and only plots
with all covariates available were used.
Results
Viability of Over-Wintered Seeds. Seed viability immediately after seed
harvest in October 2010 was 48% at Wasta Site and 67% at USFS Site (±
standard deviations of 11.6 and 13.8). In contrast, no saltcedar seeds were
viable after undergoing an over-wintering period in natural conditions.
Seedling Emergence and Survival. Temporal patterns and moisture level
effects on the number of newly emerged seedlings varied between the two study
sites. At Wasta Site, emerged seedling number varied among moisture levels
only in the first sampling period (Table 1, Figure 2). In late July, the moderate
moisture condition had the greatest number of newly emerged seedlings,
followed by the wettest and driest conditions, which did not differ significantly
from each other. The number of newly emerged seedlings declined drastically by
41
the second sampling period, during and after which there were no significant
differences in emergence with time or among moisture levels.
Numbers of emerging seedlings were substantially lower at USFS Site
than at Wasta Site (Figure 2 vs. Figure 2), but, as at Wasta Site, differences in
emergence among moisture levels varied by sampling period (Table 2). As with
Wasta Site, plots in the moderate moisture level at USFS Site had the highest
number of newly emerged seedlings in the first sampling period in late July, but
at this site the driest moisture level had fewer emerged seedlings than did the
wettest (Figure 4). This pattern remained similar two weeks later, although the
number of newly emerged seedlings was significantly lower at this time than in
the first sampling period. By sampling period 3, there were very few newly
emerging seedlings and no difference among moisture levels. This remained
true for the remainder of the monitoring period (Figure 4).
Patterns in number of surviving seedlings over time varied among
moisture levels (Tables 1 and 2), but these patterns were similar at the two sites.
The moderate moisture level had the highest mean number of surviving
seedlings; with the wettest moisture level following in surviving seedling numbers
at both sites. Also consistent with both sites, the driest moisture level yielded the
fewest surviving seedlings. Surviving seedlings decreased at each sampling
period across all moisture levels at both sites.
Number of newly emerged and surviving seedlings was related to distance
from nearest seed source only at USFS Site, where this relationship differed
42
among moisture levels (Table 2). Scatter plots for USFS Site illustrate the
relationships between the mean number of total emergence and the mean
number of surviving seedlings with distance at sampling period 5 (Figures 6 and
6.1). Beyond 400 cm, few surviving seedlings remained in moisture levels 2 and
3 unlike moisture level 1 where surviving seedlings were still present. A scatter
plot illustrates the relationship between the number of surviving seedlings at
sampling period five and the distance to nearest seed source for Wasta Site
(Figure 7). Here, beyond 400 cm very few seedlings survived at any moisture
levels. Simple regressions also demonstrate a trend of an increase of seedling
emergence with higher light availability (Table 3). Numbers of newly emerged
and surviving seedlings were related to light availability at both sites, and this
relationship was consistent across moisture levels (Tables 1 and 2). At both
sites the number of newly emerged and surviving seedlings decreased as light
availability increased (Table 3). Consequently, simple regressions demonstrated
a relationship between distance from seed source and light availability.
Regression analysis revealed that light availability increased as distance from
seed source increased (Figures 8-11). Although the ANOVA results showed
statistical significance (Tables 1and 2), none of these relationships were strong.
Less than 16% of the variance was explained by either light or distance from
seed source (Table 3, all r ≤ 0.39).
43
Discussion
This study is the first to quantify the seasonality of saltcedar seedling
emergence in the Northern Great Plains. The first major peak of seed maturation
occurred in early to mid-July, after which <5% of trees remained with blossoms
for later seed production (S. Burnette, personal observation). In contrast, in the
southwestern United States saltcedar starts producing mature seeds in early
June and continues throughout the growing season (Young et al. 2004).
Seedling emergence began soon after the production peak in early July, with the
greatest amount occurring in late July. Since no seeds were viable after
overwintering in this experiment, it is highly likely that these seedlings came from
the current growing season’s crop (S. Burnette, personal observation). Although
some trees produced seeds after the initial peak in July, very few new seedlings
emerged after early August.
Despite greater numbers of seed-bearing trees (S. Burnette, personal
observation) and higher seed viability, USFS Site had fewer emerged seedlings
than did Wasta Site (Figure 2 vs. Figure 2). An explanation for this inconsistency
may be that at Wasta Site, many of the moisture level 2 and 3 plots were located
directly under or adjacent to large seed producing trees. In conjunction with this
same plot location idea, also at Wasta Site some level 1 plots were observed to
have possible data altering variables. Many of these level one plots were
inundated in the early spring and then exposed as the water receded. Upon
exposure, a film of organic matter remained on the surface of the plots and it was
44
observed that only one seedling emerged in the plots with this organic layer (S.
Burnette, personal observation). Additionally, 6 level 1 plots were located west of
the seed producing trees and very few seedlings were found in these locations.
It is hypothesized that wind directionality affected the exposure to seeds in these
plots.
The number of surviving seedlings declined throughout the growing
season in all moisture levels, but the combination of initially lower numbers of
emerged seedlings and high mortality rates (especially at Wasta Site) in the
driest plots yielded very few surviving seedlings in the highest elevations at the
end of the growing season. This implies that not only do saltcedar seeds need
adequate moisture to germinate (Di Tomaso 1998; Young et al. 2004), but
seedlings require adequate moisture to survive their first growing season as well.
Other research has shown that saltcedar requires saturated soils for the first 2-4
weeks after germination (Zouhar 2003), and overland distance from water was
the strongest contributing factor in a model describing saltcedar distribution in the
Grand Staircase-Escalante National Monument (Evangelista et al. 2008).
Climate and early summer precipitation within the NGP may be adequate for
saltcedar emergence in July over a range of elevations. However, it would be
reasonable to hypothesize that as elevation from water source increases, the
likelihood of saltcedar seedling survival would decrease.
Although no statistically significant relationships between number of
surviving seedlings at the end of the growing season and distance from the
45
nearest seed source were found, visual examination of the data suggest some
interesting patterns. At Wasta Site, a dramatic difference in surviving seedlings
was noticed between plots which were directly adjacent to seed producing trees
compared to plots 400 cm away, where a sharp decrease in emergence was
documented. There was a sharp decline in emergence at USFS Site between 0200 cm from seed source and then very few seedlings beyond 700 cm. These
observations should only be understood as a trend, as an insufficient number of
plots were located further than 400-700 cm from seed source to make claim with
certainty.
Vegetation other than saltcedar was clipped in this study to eliminate
vegetative competition as a variable in the results, as moisture level was the
primary condition interest. Bare ground is recognized as a favorable condition for
saltcedar seedling establishment (Brotherson and Winkel 1986; Ohrtman 2011),
and many publications link competition with established vegetation as a viable
control method or preventative measure against saltcedar (Ohrtman 2011; Sher
et al. 2002; Stromberg 1997). Even though vegetation was clipped from the
plots, standing trees could not be removed; therefore tree canopy shade effect
was measured.
In this study the number of emerged seedlings decreased as light
availability increased. This finding is inconsistent with the literature (Nagler et al.
2011). This finding prompted further investigation, which discovered that the
further from seed source, light availability increased in the plots. Remembering
46
that vegetation was clipped, leaving only tree canopy, the plots with the least
amount of available light were located directly underneath a seed source; which it
is hypothesized that those plots were subjected to more seed. Additionally, this
study found that the light effect did not interact with moisture; meaning that
shading effected seedling emergence no matter the moisture level. As saltcedar
trees prefer full sun (Nagler et al. 2011), it may be that shading is one component
of vegetation cover which inhibits saltcedar seedling emergence; however the
relationship may not be strong.
Establishment of saltcedar in new areas begins with seedling emergence.
This research shows that, in the northern Great Plains, this will begin in mid- to
late July and can continue throughout the summer; though after the first major
production of seed is when the highest number of seedlings can be expected.
Majority of new seedlings and seedlings which survive the growing season can
be found within 16-30 cm of a water source. However, from within this area, the
right conditions for seedling emergence and survival must occur as well.
Shading will decrease the likelihood of emergence success regardless of
moisture, however it is not completely preventative. To best prevent
establishment on their lands, land managers should be equipped with reliable
data pertaining to favorable conditions for saltcedar emergence. Since
establishment of saltcedar begins at the seedling stage, understanding key
elements to successful seedling emergence can provide them with the proper
tools to avert an infestation. Maintaining vegetation cover for competition
47
(Ohrtman et al. 2011; Sher et al. 2002; Stromberg 1997) and reducing light
availability at the time of peak seed maturation (July) in low-lying, high moisture
areas can inhibit saltcedar seedling establishment.
48
Acknowledgements
This project was funded by the U.S. Geological Survey’s Northern Prairie
Wildlife Research Center. Diane Larson, Wes Newton, Jonathan Friedman,
Patrick Shafroth, and Patricia Johnson provided valuable comments on the
research proposal. Wes Newton and Kenneth Olson provided a valuable
statistical design approach. Thanks also to South Dakota State University’s
West River Ag Center personnel and to all the field technicians who assisted in
data collection.
49
Literature Cited
Baer, D., E. Ellick-Flettre, S. Janda, N. Marks, J. Schweitzer, and C. LeRoy. Soil
Characteristics in a Populus Common Garden.
http://academic.evergreen.edu/l/leroyc/students/soil.pdf Accessed: April,
2012
Baum, B. 1978. The genus Tamarix. The Israel Academy of Sciences and
Humanities, Jerusalem, Israel. Page 209.
Bhattacharjee, J., Taylor, J. P., Smith, L. M., & Haukos, D. A. 2008. Seedling
competition between native cottonwood and exotic saltcedar: implications
for restoration. Biological Invasions. 11:1777-1787.
Birken, A. S., and D. J. Cooper. 2006. Processes of Tamarix invation andf
development along the Lower Green River, Utah. Ecol App., 16:3:11031120.
Brock, J. H. 1994. Tamarix spp. (Salt Cedar), and Invasive Exotic Woody Plant
in Arid and Semi-arid Riparian Habitats of Western USA. John Wiley &
Sons Ltd. Ecology and Management of Invasive Riverside Plants. Pages
27-44.
Brotherson, J. D. and V. Winkel. 1986. Habitat relationships of saltcedar
(Tamarix ramosissima) in central Utah. Great Basin Nat. 46:535-541.
Di Tomaso, J. 1998. Impact, biology, and ecology of saltcedar (Tamarix spp.) in
the southwestern United States. Weed Technology. 12:326-336.
50
Everitt, B. 1980. Ecology of saltcedar-A plea for research. Environmental
Geology. 3:77-84.
Friedman, J. M., J. E. Roelle, J. F. Gaskin, A. E. Pepper, and J. R. Manhart.
2008. Latitudinal variation in cold hardiness in introduced Tamarix and
native Populus. Evol. Appl. 1:598-607.
Gaskin, J.F. and B.A. Schaal. 2002. Hybrid Tamarix widespread in U.S. invasion
and undetected in native Asian range. Proceedings of the National
Academy of Sciences 99(17):11256-11259.
Glenn, E .P., and P. L. Nagler. 2005. Comparative ecophysiology of Tamarix
ramosissima and native trees in western U.S. riparian zones. Journal of
Arid Environments 61:419-446.
Kerpez, T. A. 1997. Saltcedar Control for Wildlife Habitat Improvement in the
Southwestern United States. Washington, DC: USDI. Fish and Wildlife
Service Resource Publication, 169-185.
Natural Resources Conservation Service. PLANTS profile, Tamarix ramosissima
Ledeb., saltcedar, U.S. Department of Agriculture.
http://plants.usda.gov/java/profile?symbol=TARA. Accessed: November,
2010.
Nagler, P. L., E. P. Glenn, C. S. Jarnevich, and P. B. Shafroth. 2011.
Distribution and Abundance of Saltcedar and Russian Olive in the
Western United States. Critical Reviews in Plant Science 30:6: 508-523.
51
Ohrtman, M. K., S. A. Clay, D. E. Clay, E. M. Mousel, and A. J. Smart. 2011.
Preventing saltcedar (Tamarix spp.) seedling establishment in the
Northern Prairie Pothole Region. Invasive Plant Science and
Management 4:427-436.
Pearce, C. M. and D. G. Smith. 2007. Invasive Saltcedar (Tamarix): Its Spread
from the American Southwest to the Northern Great Plains. Physical
Geography 28:507-530.
Sher, A. A., D. L. Marshall, and J. P. Taylor. 2002. Establishment patterns of
native Populus and Salix in the presence of invasive nonnative Tamarix.
Ecological Applications 12:760-772.
Stromberg, J. C. 1997. Growth and survivorship of Fremont cottonwood,
Goodding willow, and salt cedar seedlings after large floods in central
Arizona. Great Basin Nat. 57:198-208.
Young, J. A., C. D. Clements, and D. Harmon. 2004. Germination of seeds of
Tamarix ramosissima. Journal of Range Management. 57:475-481.
Zouhar, Kris. 2003. Tamarix spp. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research
Station, Fire Sciences Laboratory (Producer). Available:
http://www.fs.fed.us/database/feis/ Accessed: May 10, 2012.
52
Table 1. ANOVA results for number of emerged seedlings and number of
surviving seedlings at Wasta Site. Moderately significant effects are in italics and
highly significant effects in bold. MOIST, PERIOD, DISTANCE and LIGHT refer
to moisture level, sampling period, distance from seed source and light
availability.
Seedlings
No.
Emerged
Factor
MOIST
PERIOD
MOIST*PERIOD
DISTANCE
DISTANCE*MOIST
LIGHT
LIGHT*MOIST
No. Surviving MOIST
PERIOD
MOIST*PERIOD
DISTANCE
DISTANCE*MOIST
LIGHT
LIGHT*MOIST
Wasta Site
DF (num, den)
2, 99
4, 420
8, 420
1, 99
2, 99
1, 99
2, 99
2, 99
4, 420
8, 420
1, 99
2, 99
1, 99
2, 99
F-ratio
2.03
38.31
3.16
0.00
1.62
7.54
1.11
2.89
15.14
2.2
0.14
1.62
8.17
1.93
p
0.1372
<.0001
0.0017
0.9975
0.2038
0.0072
0.3331
0.0604
<.0001
0.0262
0.7119
0.2039
0.0052
0.1507
53
Table 2. ANOVA results for number of emerged seedlings and number of
surviving seedlings at USFS Site. Moderately significant effects are in italics and
highly significant effects in bold. MOIST, PERIOD, DISTANCE and LIGHT refer
to moisture level, sampling period, distance from seed source and light
availability.
Seedlings
No.
Emerged
No.
Surviving
Factor
USFS Site
DF (num/den)
F-ratio
p2
MOIST
PERIOD
MOIST*PERIOD
DISTANCE
DISTANCE*MOIST
LIGHT
LIGHT*MOIST
2, 111
4, 464
8, 464
1, 111
2, 111
1, 111
2, 111
3.69
81.53
6.64
8.14
3.96
4.88
1.09
0.0281
<.0001
<.0001
0.0052
0.0217
0.0292
0.3408
MOIST
PERIOD
MOIST*PERIOD
DISTANCE
DISTANCE*MOIST
LIGHT
LIGHT*MOIST
2, 111
4, 464
8, 464
1, 111
2, 111
1, 111
2, 111
5.23
25.19
3.99
7.83
4.33
3.7
1.48
0.0067
<.0001
0.0001
0.0061
0.0155
0.0569
0.2314
54
Table 3. Simple regressions of total number of emerged seedlings (over the
growing season) and number of alive seedlings at the final sampling period on
light availability.
Seedlings
Emerged
Site
Wasta
USFS
Light
Intercept
1052 (249)
515 (115)
Alive (Period 5)
Wasta
USFS
238 (100)
88 (52)
Slope
-1.23 (0.60)
-0.83 (0.33)
r
0.20
0.23
p value
0.041
0.013
-0.19 (0.24)
-0.08 (0.15
0.07
0.05
0.425
0.563
Table 3.1 Simple regressions of total number of emerged seedlings (over the
growing season) and number of alive seedlings at the final sampling period on
distance from seed source.
Seedlings
Emerged
Alive
Site
Wasta
USFS
Distance
Intercept
134.7 (22.0)
91.2 (14.9)
Slope
-0.12 (0.06)
-0.13 (0.04)
r
0.2
0.28
Wasta
USFS
369.5 (63.13)
219.1 (24.4)
-0.31 (0.16)
-0.30 (0.07)
0.18
0.20
p value
55
Figure 1. Picture of marked saltcedar seedlings at USFS Site taken on August
24th, 2011(S. Burnette).
56
Figure 2. Least squares means of total number of newly emerged seedlings at
Wasta Site from each moisture category (1= wettest, 2= moderate, 3= driest) at
each sampling period. Letters above bars indicate significant (p <0.10)
Emergence (m-2)
differences between means across the whole figure.
900
800
700
600
500
400
300
200
100
0
-100
a
b
b
c
1
2
3
1
c
c
c
2
3
1
c
2
c
c
3
1
c
c
2
3
c
1
c
c
2
3
25-Jul-11 9-Aug-11 19-Aug-11 2-Sep-11 27-Sep-11
57
Figure 3. Least squares means of total number of newly emerged seedlings at
USFS Site from each moisture category (1= wettest, 2= moderate, 3= driest) at
each sampling period. Letters above bars indicate significant (p <0.10)
differences between means across the whole figure.
300
a
250
Emergence (m-2)
200
b
150
c
100
c
d
50
de
e
e
de
e
e
de
e
e
e
1
2
3
1
2
3
1
2
3
0
1
-50
2
3
21-Jul-11
1
2
3
11-Aug-11 24-Aug-11
7-Sep-11
28-Sep-11
58
Figure 4. Least squares means of total number of surviving seedlings at Wasta
Site from each moisture category (1= wettest, 2= moderate, 3= driest) at each
sampling period. Lowercase letters above bars indicate significant (p <0.10)
differences between means within moisture level, and uppercase letters indicate
significant differences within sampling period.
d
Y
1000
Surving Seedlings (m-2)
900
800
e
XY
700
600
a
X
i
X
500
400
ab
X
i
Y
b
X
f
XY
300
g
b XY
X
j
Y
200
b
X
g
X
k
Y
100
k
Y
0
1
2
3
25-Jul-11
1
2
3
9-Aug-11
1
2
3
19-Aug-11
1
2
3
2-Sep-11
1
2
3
27-Sep-11
59
Figure 5. Least squares means of total number of surviving seedlings at USFS
Site from each moisture category (1= wettest, 2= moderate, 3= driest) at each
sampling period. Lowercase letters above bars indicate significant (p <0.10)
differences between means within moisture level, and uppercase letters indicate
significant differences within sampling period.
Surving Seedlings (m-2)
300
250
200
b
Y
b
Y
a
Y
a
X
150
a
X
a
X
ac
X
d
X
c
Y
100
a,d
X
cd
Y
50
e
Y
f
X
f
X
g
Y
0
1
2
3
21-Jul-11
1
2
3
1
2
3
11-Aug-11 24-Aug-11
1
2
3
7-Sep-11
1
2
3
28-Sep-11
60
Figure 6. Scatterplot showing total seedling emergence at USFS Site from each
moisture level in relation to distance (cm) from nearest seed source.
-2
Total # Emerged Seedlings (m )
2500
Moisture Level 1 (wettest)
Moisture Level 2 (moderate)
Moisture Level 3 (driest)
2000
1500
1000
500
0
0
200
400
600
800
Distance from Nearest Seed Source (cm)
1000
1200
61
Figure 6.1 Scatterplot showing number of surviving seedlings at the end of the
growing season at USFS Site in relation to distance (cm) from nearest seed
source.
Moisture Level 1 (wettest)
Moisture Level 2 (moderate)
Moisture Level 3 (driest)
-2
# Seedlings Alive at End of Season (m )
800
600
400
200
0
0
200
400
600
800
Distance from Nearest Seed Source (cm)
1000
1200
62
Figure 7. Scatterplot of number of surviving seedlings at Wasta Site at the end of
-2
# of Seedlings Alive at End of Growing Season (m )
the growing season in relation to distance from seed source (cm).
2500
Moisture Level 1 (wettest)
Moisture Level 2 (moderate)
Moisture Level 3 (driest)
2000
1500
1000
500
0
0
200
400
600
800
1000
Distance from Nearest Seed Source (cm)
1200
1400
63
Figure 8. Scatterplot demonstrating the relationship between light availability and
distance from seed source at both sites. Reference A is Wasta Site and
reference B is USFS Site.
64
CHAPTER 4
Saltcedar in the Northern Great Plains: Cultural Considerations
Abstract
Saltcedar (Tamarix Spp.) has been on the invasive species radar for decades in
the United States prompting numerous biological studies. Though ecological
effects of saltcedar are widely investigated, little attention is given to cultural
considerations. Invasive species can and do affect social and cultural systems.
This study’s goal was to gain understanding of the current and possible effects
and concerns of saltcedar on the Lakota communities. Interviewed participants
were members of a South Dakota federally recognized tribe and/or residents of a
South Dakota Lakota reservation. A priority was to obtain feedback from various
internal groups and subgroups. These groups included: 1) ranchers, 2)
traditional tribal members and, 3) resource managers. Three participants were
purposely selected to represent each sub-category, giving a total of 15
interviewees. Three main themes were highlighted from the participant’s
responses, stressing concern for 1) preserving culturally significant vegetation, 2)
ranching, and 3) managing land, time, and resources. Understanding and
emphasizing these concerns in future saltcedar education and management
efforts may enhance their effectiveness when working with tribal lands and
people as well as contribute to improved cultural and environmental
conservations.
65
Introduction/Literature Review
Within South Dakota’s boundaries are nine Native American Reservations
of Lakota, Nakota, and Dakota peoples (Figure 1). These reservations and their
tribal members depend upon the land for individual and family ranching
endeavors, revenue generated from leasing their lands, and various flora and
fauna cultural needs, among other things.
The 2007 agricultural census reports approximately1 3,678,300 ha of tribal
land in use for agricultural production throughout the nine South Dakota
reservations, with 1,544,187 ha operated by tribal members (McCurry 2010).
The reservations depend upon the riparian networks to maintain this agricultural
production primarily for the use of natural water sources for livestock.
Even with the widely researched adverse effects of introduced species on
the environment, little research has taken place as to their effect on social
systems (Pfeiffer and Voeks 2008). Native flora are a significant factor in the
cultural identity of indigenous societies throughout the world (Stepp et al. 2002).
Semi-domesticated and domesticated species have been utilized, tended to, and
conserved by native peoples for millennia, which has resulted in individual,
unique cultural societies (Pfeiffer and Voeks 2008).
Invasive species have the potential to deprive communities of the
biodiversity necessary to maintain their cultural resilience. Culturally significant
1
The data collected from the Flandreau Santee Sioux Tribe was not disclosed in this census report.
66
natural resources may decline in abundance or have restricted access as a result
of an establishment of invasive species (Pfeiffer and Voeks 2008). For example,
basket weavers from California were impacted when increasing populations of
starthistle (Centaurea solstitialis), scotch broom (Cytisus scoparius), and stinging
nettle (Urtica gracilis) within their ancestral gathering groves displaced redbud
(Cercis canadensis) and deergrass (Muhlenbergia rigens), which are traditional
weaving materials (Pfeiffer and Ortiz 2007). Through water deprivation and
habitat encroachment, saltcedar has significantly decreased the populations of
culturally significant vegetation such as cottonwood (Populus fremontii), willow
(Salix exigua, S. lasiandra), sandreed (Calamovilfa gigantea) and yucca (Yucca
spp.) in the southwest. The Hopi tribe has been forced to uproot and replant
these species closer to their reservation for use and preservation (Pfeiffer and
Voeks 2008).
Displacement of culturally significant native species by invasive species
can create a ripple effect by also displacing traditions that are tied to the native
species (Pretty 2002). Local natural resources define cultural identity through
folk taxonomies, ethnobiological practices, songs, and oral stories (Pfeiffer and
Voeks 2008). Languages live within the names of flora, fauna, and other natural
resources through their definitions; it is common for the name of a plant or place
to be a description of what it looks like or how it is used. Thus, when native
species decline, community members face challenges in maintaining or reviving
their cultural traditions.
67
Chemically treating invasive species has caused an indirect effect on
culturally significant vegetation and, therefore, the cultural societies themselves
(Mackenzie 2003). Pesticide drift onto native vegetation used in basket weaving
has been documented to stunt growth and deform the plants, making them
unusable (Pfeiffer and Voeks 2008).
While the biological spread of saltcedar has been documented in the
region (Nagler et al. 2011) and cultural impact of the loss of native species has
been well documented elsewhere, no research has explored the impact of
saltcedar on Lakota land and people in South Dakota.
Therefore, the research goal was to increase understanding of Native
American, specifically Lakota, cultural perspectives of and impacts felt from
invasive saltcedar. Qualitative in-depth interviews were chosen as the
methodology for addressing these issues. This method was chosen because the
words of the people themselves can best address how a saltcedar establishment
throughout the reservations may impact them. This study was part of a larger
research effort that also explored saltcedar seedling emergence in South Dakota
riparian conditions.
Materials and Methods
All cultural impact interviews were done with those that are members of a
federally recognized tribe in South Dakota. Individual interviews were conducted
with each participant. A list of interview questions were used to serve as a guide
68
throughout the interview (Appendix C), but a conversational format was used as
it is most appropriate with this culture. Photographs displaying riparian habitats
that have been invaded by saltcedar, areas cleared of a saltcedar invasion, as
well as local riparian habitats were utilized as visual aids during the interviews
(Appendix C). This study explored the following research questions:

What are your experiences with saltcedar on the reservation?

How do you think or feel saltcedar is currently impacting the
reservation?

Do you have any concerns about the spread of saltcedar on the
reservation, if so what are your concerns and why are they
important?

Would more saltcedar on the reservation impact your life? How
so?

Are there cultural implications of saltcedar coming to the
reservation and spreading? If so what are these and why are these
cultural implications important (or not important) to consider?

Are you aware of any historical and/or cultural uses for the
saltcedar? What are these?

Is there anything else you’d like to add related to saltcedar on the
reservation and cultural impacts?
Notes were taken pertaining to the content of each interview. Video
and/or voice recorders were not used. The interviews took place at a location
69
chosen by the participant; commonly the interviewer traveled to the places of
work or the homes of the participants.
Participants were members from any of the federally recognized tribes
located within South Dakota. A priority in the research was to obtain feedback
from various internal groups. These groups and sub-groups were defined as: 1)
Ranchers, a) Land Owners, b) Land Leasers; 2) Traditional Practitioners
(Including those who regularly participate in cultural and spiritual practices, speak
their native language, etc…); and 3) Resource Managers, a) Park and
Recreation, b) Tribal Land Officials.
Three participants were purposively selected to represent each subcategory, giving a total of 15 interviewees. Qualifications to participate in the
research included being an enrolled member of the targeted tribe. In accordance
with Tribal policy, the interviewer obtained Institutional Review Board (IRB)
approval from the Rosebud and Pine Ridge reservations prior to the start of the
study.
Participants were sought out by the interviewer through previously
established personal and/or professional contacts as well as from referrals made
by those already established contacts. Participants were assigned to a group or
subgroup based upon occupation. The interviewer established initial contact with
all prospective participants through telephone and/or emailing venues. However,
when opportunities arose, the interviewer took advantage of social and/or
professional in- person encounters to inquire about participation in the research.
70
All possible participants were given an overview of the project in its entirety as
well as a detailed description of what their role would be as an interviewee
(Appendix C). All individuals were given the choice of whether or not they would
like to participate.
Each participant was interviewed once. Follow-up discussions were
considered if necessary for either the researcher or subject. Each participant
was invited to contact the interviewer should he or she have additional comments
to express. The interviews ranged from 20 minutes to 1 hour and were
conducted during breaks at various conference meetings, over lunch, or at the
home of the participant.
A gift bag consisting of items such as coffee and tobacco were given to
each participant. In Lakota culture it is appropriate to give a gift to an individual
of whom you are asking something. Tobacco and coffee are most commonly
used for this and are accepted items of exchange.
At the participants' discretion, he or she may have elected to be
anonymous throughout the duration of the research and thereafter. All
documents pertaining to the interviews were stored in a locked compartment at
the office of the interviewer.
Data Analysis. Full field notes from interviews were transcribed verbatim within
48 hours of each interview. Transcripts included the researcher’s observer
comments and observations on subjects’ responses. Simple quantitative
71
analysis counted and compared responses assigning common themes while
considering groups and subgroups of participants.
A content analysis of key themes related to the research questions was
conducted. A multi-stage coding scheme was developed and applied to aid in
condensing qualitative responses around key emergent themes.
For the first stage of coding, transcripts were read, reviewed and
highlighted in color codes according to key themes identified in the literature. A
second stage of coding further identified and clarified responses in relation to
pre-existing models and theoretical perspectives. During a third stage of coding,
transcripts were re-read with additional analytical notes made in the transcript
margins – these notes comprised of new and emergent themes (and additional
insights), not identified in previous research.
To help ensure the project’s reliability, double coding was employed. This
means that transcripts were coded in two distinct ‘rounds’ of analysis, one day
apart, until code-recode reliability approached 100 percent.
To help establish validity of the respondents, drafts of findings and
conclusions chapters were reviewed by a tribal member (non-participant in the
research) who is knowledgeable about the issues. This helped check the
accuracy and validity of the author’s conclusions and provide suggestions
towards alternate interpretations.
72
Results
Personal Experiences. When asked about their experiences with saltcedar,
three participants had never heard of saltcedar; all three of these participants
were traditional practitioner interviewees. Those who had heard of saltcedar but
had never had direct interaction were two land owners, one rancher, and one
council member (who is classified in the tribal land office group). Three
participants, one from each group of land manager, land owner, and rancher
have had minimal experience with saltcedar, such as being able to identify it or
know of others who have had problems with saltcedar on their lands. The
remaining participants (four) had all had extensive experience dealing with
saltcedar on the reservations. Their range of experience spans from being part
of chemical treating crews to head management tasked with seeking out funding
to tackle invasive species problems. Interviewees with this extensive handling of
saltcedar were two tribal land office employees and two land managers (Table 1).
Current Impacts on Reservations. Responses to the question relating to each
participant’s knowledge of how saltcedar is currently impacting the reservations
resulted in an array of concerns (Table 2). The most common response, from
seven participants (47%), expressed realization that saltcedar is present. These
seven participants also felt that as of right now saltcedar is not as problematic as
it could be but also stated that due diligence is required to keep it that way. One
of these seven interviewees stated that due to budget cuts, proper funding may
not be available to ensure that saltcedar upkeep be maintained.
73
Additionally, impacts caused by saltcedar on ranching and farming
endeavors were viewed as a current concern by the two ranchers. All of these
participants felt that saltcedar will be an enduring problem for the reservations.
All three traditional practitioners and two land owners were not sure or aware of
how saltcedar was impacting the reservation as of present. Interviewees in the
ranching and management groups, one from each, expressed concern that
native vegetation is currently being threatened by the presence of saltcedar. The
one reservation land manager expressed further concern about the overall
condition of riparian habitat and landscape.
Biggest Concerns. When asked to discuss their concerns about the spread of
saltcedar within the reservations (Table 3), eight participants- three traditional
practitioners, one rancher, one land owner, two tribal land officials, and one land
manager responded with worry of the displacement of native vegetation. Loss of
native vegetation was the top concern amongst the participants. Loss of control
of saltcedar and the continual spread throughout the reservations was the
second most commonly expressed concern. Those worried about continual
spread included two ranchers, one land manager and two tribal land officials.
Other frequent responses included 1) use of chemical treatment, 2) range
quality/water access for livestock, and 3) destruction of habitat/environment.
Those concerned with the use of chemical treatment included one traditional
practitioner, two tribal land officials, and one rancher. Responding with concerns
over ranching endeavors were interviewees from the groups ranchers (two), land
74
management (one), and land owner (one). One rancher stated, “…ranching is
my life; my cattle need to be able to get to the river for water.” All four
respondents but one rancher were primarily concerned with water access and
availability for livestock; this second rancher stated that spread of saltcedar
would have an overall negative effect on ranching operations. Concerns of soil
quality impacted by saltcedar were mentioned by one of the ranchers. Necessity
of locating and obtaining funding for treatment was a concern for one rancher
and two tribal land officials.
Direct Impacts. When asked about how a saltcedar infestation would directly
impact the interviewees’ lives (Table 4) the most frequent response centered on
the time and workload which would be increased by the infestation. All three
tribal land officials, two land managers, and one rancher stated that should
saltcedar presence increase on the reservations they would be tasked with
seeking out additional funds and labor resources for eradication. Additionally,
their time was of concern; time put into planning, resourcing, and educating land
owners. Interviewees in the cultural group and one land owner felt that saltcedar
could not only impact their use of native vegetation but could threaten culture in
itself by endangering significantly used plants; as expressed by one of the land
owners “…I am a sundancer. I depend upon the cottonwoods and the willows for
this ceremony.” Two of the ranchers were concerned with how an establishment
of saltcedar would alter the land itself and how it might affect their operations.
Impacts to ranching operations were a concern for the three ranchers as well as
75
one land owner and one land manager. One cultural practitioner was curious if
there was a use for saltcedar.
All participants discussed in general and in specifics about how the
displacement of native vegetation and habitat would negatively impact the Lakota
culture. Participants generally spoke of some plants having ceremonial or
medicinal usages; as expressed by one of the traditional practitioners “…our
culture depends on the cottonwood tree for sundance…and we use sweetgrass
in ceremonies.” One land owner stated that she participates in a specific
ceremony and depends upon the cottonwood tree (Populus Spp.), willows (Salix
Spp.), and other plants for this ceremony. Plant species which provide general
use, such as, teas or food were mentioned by two land managers. Two cultural
practitioners and 1 rancher stated that saltcedar has no cultural value. A cultural
practitioner discussed how native vegetation has a vital role in the Lakota culture;
specifying certain uses in ceremonies and as medicine as well as the language
survival. This interviewee discussed how the Lakota names of plants, creeks,
and areas are all descriptive; that a plant’s name may describe how it is used or
where it may be located. None of the participants knew of any cultural uses for
saltcedar.
Discussion
From this research valuable information has been obtained pertaining to
the views of invasive plant species, particularly saltcedar, of the Lakota people;
76
as well as where priorities lie in the event of an incursion. Pfeiffer et al. (2008)
categorizes invasive species in a cultural context as 1) culturally enriching, 2)
facilitating, and 3) impoverishing. These authors recognize that some invasive
species may mesh within these categories (Pfeiffer et al. 2008); however the
results of this study demonstrate that, at the present, saltcedar is or has the
potential to be an impoverishing invasive tree to the Lakota people. Culturally
speaking, the uses and cultural endearment of native plant species by far
outweighed any enriching or facilitating characteristics of saltcedar. Saltcedar
was not only viewed as a biological threat but as a threat to culture itself. One of
the traditional practitioners said “Our plants have stories that go back for
generations, these stories are part of who we are”. Culture is not so much
defined solely as the race of a people but of the characteristics and practices
which encompass the past, present, and generational teachings of the people.
Vegetation which depend upon riparian habitat for existence are part of what
define the Lakota culture and there are no replacements.
The second most common concern found in this study dealt with land
operations and land management. Presently, reservation lands in South Dakota
are primarily used for ranching operations. Livelihoods are made through leasing
land, ranching, or land management. Many of the ranching operations
throughout the reservation rely on natural water sources for livestock. A
repeated concern was water availability and access to water. It would be a
tremendous hardship on the tribes and land owners to establish alternative water
77
sources, such as digging wells. Funding for alternative’s such as this is difficult
to obtain. Billions of dollars have been lost due to saltcedar establishment
throughout rangelands in the U.S. (Zavaleta 2000). If saltcedar establishment
takes hold on reservation lands, additional funding would be required for
eradication.
Understanding biological invasions in a cultural context provides the
necessary information to better educate people about possible implications.
Knowing what is important to people is vital for triggering appropriate concern
and action. People should understand exactly how invasive species will affect
them just as much as those in management positions should understand
sociological implications. Encompassing cultural considerations with biological
implications provides a more holistic approach to invasive species management.
78
Literature Cited
Baum, B. 1978. The genus Tamarix. Academy of Sciences and Humanities.
Kerpez, T. A. 1997. Saltcedar Control for Wildlife Habitat Improvement in the
Southwestern United States. Washington, DC: USDI. Fish and Wildlife
Service Resource Publication, 169-185.
Mackenzie, A. (n.d.). Forest herbicide plan threatens basket weavers. Retrieved
May 20, 2010, from Terrain:
http://ecologycenter.org/terrain/issues/summer2003/forest-herbicide-planthreatens-basketweavers/
McCurry, M. 2010. Ag Census 2002-2007 Reservations. Brookings, South
Dakota: South Dakota State University.
Nagler, P. L., E. P. Glenn, C. S. Jarnevich, and P. B. Shafroth. 2011.
Distribution and Abundance of Saltcedar and Russian Olive in the
Western United States. Critical Reviews in Plant Science, 30:6: 508-523.
Natural Resources Conservation Service. PLANTS profile, Tamarix ramosissima
Ledeb., saltcedar, U.S. Department of Agriculture.
http://plants.usda.gov/java/profile?symbol=TARA. Accessed: November,
2010.
Pfeiffer, J. and Robert A. Voeks. (2008). Biological invasions and biocultural
diversity: linking ecological and cultural systems. Environmental
Conservation 35 (4):281-293.
79
Pfeiffer, J. and Elizabeth Huerta Ortiz. 2007. Invasive plants impact California
native plants used in traditional basketry. Fremontia 35(1):7-13.
Pimentel, D. 2002. Biological Invasions: Economic and Environmental Costs of
Alien Plant, Animal, and Microbe Species. Boca Raton, FL, USA: CC
Press.
Pretty, J. 2002. Landscapes lost and found. In: Agri-culture: Reconnecting
People, Land and Nature, ed. J. Pretty, pp. 10-26. London, UK: Earthscan
Publications.
Sher, A. A., D. L. Marshall, and J. P. Taylor. 2002. Establishment patterns of
native Populus and Salix in the presence of invasive nonnative Tamarix.
Ecological Applications 12:760-772.
State, S. D. (2010, February 23). Tamarisk (Salt Cedar). Retrieved February 23,
2010, from Distribution Map:
http://www.sdgfp.info/Wildlife/AquaticNuisance/SaltCedarDistributionMap.
aspx
Stepp, J. W. 2002. Ethnobiology and Biocultural Diversity. Athens, GA: The
International Society of Ethnobiology.
Zavaleta, E. 2000. The economic value of controlling an invasive shrub. Ambio
29:462-467.
80
Tables
Table 1. Responses to the question “What are your experiences with saltcedar
on the reservation?”
Participants
None
A (Rancher)
J (Rancher)
N (Rancher)
B (Tribal Practitioner)
F (Tribal Practitioner)
K (Tribal Practitioner)
C (Land Manager)
H (Land Manager)
O (Land Manager)
D (Land Owner)
E (Land Owner)
I (Land Owner)
G (Land Official)
L (Land Official)
M (Land Official)
Response
Theme
Nothing
Direct
X
Minimal
Extended
X
X
X
X
X
X
X
X
X
X
X
X
X
X
81
Table 2. Responses to the question “How do you think or feel saltcedar is
currently impacting the reservation?”
Participants
Response Theme
Threat/
Not problematic
A (Rancher)
J (Rancher)
N (Rancher)
B (Tribal Practitioner)
F (Tribal Practitioner)
K (Tribal Practitioner)
C (Land Manager)
H (Land Manager)
O (Land Manager)
D (Land Owner)
E (Land Owner)
I (Land Owner)
G (Land Official)
L (Land Official)
M (Land Official)
Not Sure
Native Veg.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Ranching
X
82
Table 3. Responses to the question “Do you have any concerns about the spread
of saltcedar on the reservation, if so what are your concerns and why are they
important?”
Participants
Response
Theme
Spread/
Native Veg.
Use of
Habitat
Uncontrolled Displacement Chemicals Funding Ranching Destruction
A (Rancher)
X
X
X
J (Rancher)
X
X
N (Rancher)
X
X
X
X
B (Tribal Practitioner)
X
X
X
F (Tribal Practitioner)
X
K (Tribal Practitioner)
X
C (Land Manager)
X
H (Land Manager)
X
X
X
O (Land Manager)
X
X
D (Land Owner)
X
E (Land Owner)
X
I (Land Owner)
X
G (Land Official)
X
X
X
X
L (Land Official)
X
X
X
M (Land Official)
X
X
83
Table 4. Responses to the question “Would more saltcedar on the reservation
impact your life? How so?”
Response
Theme
Participants
A (Rancher)
J (Rancher)
N (Rancher)
B (Tribal Practitioner)
F (Tribal Practitioner)
K (Tribal Practitioner)
C (Land Manager)
H (Land Manager)
O (Land Manager)
D (Land Owner)
E (Land Owner)
I (Land Owner)
G (Land Official)
L (Land Official)
M (Land Official)
Native Veg.
Displacement
X
Time/work load
Ranching
X
X
X
Possible
Uses
X
X
X
X
X
X
X
X
X
X
X
X
84
Figures
Figure 1. Map of South Dakota Native American reservations highlighted in pink
and major waterways lined in blue (nationalatlas.gov)
85
Thesis Conclusions
Establishment of saltcedar in new areas begins with seedling emergence.
This research shows that, in the Northern Great Plains, this will begin in mid- to
late July and can carry throughout the summer; although the highest number of
seedlings can be expected after the first major production of seed. Majority of
new seedlings and seedlings which survive the growing season can be found
within 16-30 cm of a water source; however the right conditions for seedling
emergence and survival in this area are important as well. Shading will decrease
the likelihood of emergence success in all levels of moisture however it is not
completely preventative. To best prevent establishment on their lands, land
managers should be equipped with reliable data pertaining to favorable
conditions for saltcedar emergence. Since establishment of saltcedar usually
begins at the seedling stage, understanding key elements to successful seedling
emergence can provide them with the proper tools to head off an infestation.
Maintaining vegetative cover for competition (Ohrtman et al. 2011; Sher et al.
2002; Stromberg 1997) and reducing light availability at the time of peak seed
maturation (July) in low-lying, high moisture areas can inhibit saltcedar seedling
emergence.
Each year, individual saltcedar plants produce millions of seeds and, at
least for the two populations in this study, viability of these seeds was quite high
(50-70%). Many of these viable seeds will not emerge to become seedlings,
however, because they do not fall on the proper conditions. Understanding
86
factors that affect saltcedar emergence and establishment from seed can assist
land managers in identifying sites with conditions that might encourage or inhibit
saltcedar emergence. Clayey, moist soils with little to no vegetation but with a
healthy population of microbes pose the most risk for saltcedar establishment in
the Northern Great Plains. Therefore, maintaining healthy, established
vegetation cover in riparian areas, particularly during the peaks of seed
maturation, would be a reasonable first line of defense for land managers against
a saltcedar invasion.
Understanding biological invasions in a cultural context provides the
necessary information to better educate people about possible implications.
Knowing what is important to people is vital for triggering appropriate concern
and action. People should understand exactly how invasive species will affect
them just as much as those in management positions should understand
sociological implications. Encompassing cultural considerations with biological
implications provides a more holistic approach to invasive species management.
87
APPENDIX A
Figure 1. Picture of smooth brome grown in clayey soil used for Chapter 2’s
vegetation cover test.
88
Figure 2. Picture of inland saltgrass grown in sandy soil used for Chapter 2’s
vegetation cover test.
89
APPENDIX B
Figure 1. Picture of a level 1 plot located at Wasta Site. Shows a layer of
organic material left on the plot once water receded. The lone saltcedar seedling
was the only seedling documented having grown on the organic layer.
90
Figure 2. Picture of saltcedar seeds at peak maturity at Wasta Site. Photograph
was taken on July 7th, 2011.
91
Figure 3. Scatterplot of total emergence at Wasta Site in relation to light
availability.
S ite A
T o t a l # E m e r g e d S e e d lin g s
4000
3000
2000
1000
0
0
100
200
300
400
500
600
L ig h t
Figure 4. Scatterplot of total emergence at USFS Site in relation to light
availability.
S ite B
2500
T o t a l # E m e r g e d S e e d lin g s
2000
1500
1000
500
0
0
100
200
300
L ig h t
400
500
92
Figure 5. Scatterplot of seedlings alive at sampling period 5 at Wasta Site in
relation to light availability.
S ite A
N u m b e r S e e d lin g s A liv e a t 5
2500
2000
1500
1000
500
0
0
100
300
APPENDIX
C4 0 0
200
500
600
L ig h t
Figure 6. Scatterplot of seedlings alive at sampling period 5 at USFS Site in
relation to light availability.
S ite B
N u m b e r S e e d lin g s A liv e a t 5
800
600
400
200
0
0
100
200
300
L ig h t
400
500
93
Appendix C
Document 1.
Interview Introduction
Hi! My name is Sarah Burnette. I am a graduate student at South Dakota
State University in Biological Sciences. I am conducting research pertaining to
the ecology of the saltcedar seed. Saltcedar is a non-native tree that can have
an impact on riparian habitats. I will be testing the success of saltcedar
emergence under various conditions which compare to conditions along the
riparian habitats of most of South Dakota. Results from this study will aid land
managers and land users in identifying ecological conditions which would favor
saltcedar establishment through seed reproduction. Providing this information
would allow for improved land management objectives and plans.
Another goal is to establish a better understanding as to how an
establishment of saltcedar would impact Lakota people on the Pine Ridge
Reservation. Analysis of these ethnographic interviews will establish a better
understanding of the sociological impacts created by a saltcedar establishment
from the viewpoint of the Lakota people. The analysis could help establish
guidelines of better methods to inform the public about saltcedar.
I’m attempting to interview a series of tribal people on the reservation to
gain their important cultural perspectives on saltcedar. I appreciate your
willingness to visit with me about these issues. The interview should take about
30 minutes to an hour. Your responses will be kept confidential and I will share
94
the results of my work with you when it is complete. Do you have any questions
or concerns before we begin with questions?
Document 2.
Participant's Agreement
I am aware that my participation in this interview is voluntary. I understand the
intent and purpose of this research. If, for any reason, at any time, I wish to stop
the interview, I may do so without having to give an explanation.
The researcher has reviewed the individual and social benefits and risks of this
project with me. I am aware the data will be used in a Graduate Thesis Project
that will be publicly available at the South Dakota State University Library as well
as possible journals. I have the right to review, comment on, and/or withdraw
information prior to the Thesis Project’s submission. The data gathered in this
study are confidential with respect to my personal identity unless I specify
otherwise.
If I have any questions about this study, I am free to contact the student
researcher or the faculty adviser (contact information given above). If I have any
questions about my rights as a research participant, I am free to contact the Vice
President for Research for the Institutional Review Board at: 605-688-6975
I have been offered a copy of this consent form that I may keep for my own
reference.
95
I have read the above form and, with the understanding that I can withdraw at
any time and for whatever reason, I consent to participate in today's interview.
_______________________
Participant's signature
_______________________
Interviewer's signature
_______________
Date
________________
Date
Thank you for your participation today and for sharing your perspectives
on saltcedar on the reservation. Please let me know if you have any concerns,
or further ideas or suggestions for my work. As I stated earlier, I will share the
results of my research with you upon completion. I greatly appreciate your time
and would like to present you with this small token of appreciation. Thank you
again.
96
Document 3.
Saltcedar Impacts Questionnaire
GENDER F M
AGE _________
POSITION
____________________________________________________________
TRIBAL
AFFILIATION__________________________________________________
From your own cultural perspective would you describe yourself as:
Native American
Mostly Native American
Bicultural
Mostly Non-Native American
Non-Native American
What are your experiences with saltcedar on the reservation?
How do you think or feel saltcedar is currently impacting the reservation?
Do you have any concerns about the spread of saltcedar on the reservation, if so
what are your concerns and why are they important?
Would more saltcedar on the reservation impact your life? How so?
97
Are there cultural implications of saltcedar coming to the reservation and
spreading? If so what are these and why are these cultural implications
important (or not important) to consider?
Are you aware of any historical and/or cultural uses for the saltcedar? What are
these?
Is there anything else you’d like to add related to saltcedar on the reservation
and cultural impacts?
98
Figure 1. and 1.1
Visual Aids
Infestation of saltcedar in Salt Lake county of Midvale, Utah (Salt Lake County)
Saltcedar infestation (BIOQUEST)
99
APPENDIX D
Disposal
Chapter 2. Controlled Experiment
Upon completion of the study, all grown seedlings, remaining seed,
germinated seeds, and used soil were placed in a drying oven for 24 hours at
90°C. After drying all materials were disposed of. All unused soil was placed
back in a natural habitat.
Chapter 3. Field Experiment
After the final sampling period, all plot markers and flags were collected
from each plot. Additionally, all markers and rings were removed from surviving
seedlings.
Chapter 4. Cultural Considerations
After submission of the Thesis document, all interview questionnaires and
notes were shredded and disposed of.