STATEMENT OF WORK
Ecological Studies of Willow (Salix caroliniana)
I.
BACKGROUND
The headwater region of the Upper St. Johns River in east-central Florida contains a vast expanse
of wetlands dominated by shallow marshes, wet prairies, sloughs, shrub swamps, and forested
wetlands. Over the past 40 years there has been significant encroachment of woody shrubs,
primarily Carolina willow (Salix caroliniana Michx.), into areas that were historically
herbaceous marsh. Woody shrub encroachment has been attributed to hydroperiod reductions,
reduced frequency of fire, and disturbance caused by major construction activities. However,
research aimed at understanding the ecology of willow invasion has been lacking.
The St. Johns River Water Management District (District) is investigating methods of restoring
herbaceous wetlands through mechanical and chemical means. Once restoration is achieved, the
District will need to manage herbaceous marshes so that reversion to shrub wetland is
minimized. To accomplish this task, the District will require knowledge of those factors that
facilitate willow invasion and loss of herbaceous wetlands.
II.
OBJECTIVES
The objectives of this project are:
1) To determine how environmental factors such as soil type (peat, sand, clay), hydrology
(saturated, flooded, dry), and nutrients (phosphorus, nitrogen, micronutrients) affect willow
seed germination, growth, and survival.
2) To determine how fire, hydrology, and interspecific competition affect the distribution of
willow in marsh habitats.
III.
SCOPE OF WORK
The University of Central Florida (University) envisions the current invasion by willow as a
multi-phase (Introduction → Colonization → Naturalization) and multi-scale process
(individual, population, and region) that will be addressed in parts and integrated into a
predictive, demographic model (Fig. 1) that can inform management decisions. The University
will combine greenhouse, field and natural experiments with short and long-term field
observations, dendrochronology, and modeling to evaluate the invasive potential and population
trends of willow within the regional landscape. The University proposes to parameterize the
model with probabilistic estimates of vital rates that estimate the relative performance of willow
in contrasting environments to evaluate its relative success across regional ecosystems and map
expected invasion fronts using GIS. The goal is to identify areas susceptible to colonization and
expansion of willow, identify practical management techniques, and prioritize management on
areas critical for halting and eventually reversing the current invasion of herbaceous wetlands.
The University’s experiments shall characterize germination in soils with contrasting texture and
moisture and demonstrate causal relationships. The University shall describe seedling and adult
survival, growth, and mortality in different habitats and estimate seed production and dispersal.
The University shall compare growth rates of willows in the natural setting to those observed in
greenhouse trials and identify reliable measures of willow growth to determine differences in age
structure and growth rates among different willow populations. The University’s models (Fig. 1)
shall integrate these data to evaluate the potential population dynamics of willow in different
habitats within the St Johns River drainage, including responses to fire. Model predictions can
then be used to map risks of willow invasion, colonization, and naturalization, and to identify
critical areas for management action.
IV. TASK IDENTIFICATION AND SUMMARY
Task 1: Finalize Research Plan
The initial task of the project shall be the development of a research plan that describes the
various project elements and how these are to be integrated to achieve the overall objectives.
Project elements are specific experiments conducted in the greenhouse/laboratory, in situ, or in
mesocosms. Location, transportation, and access to field sites shall be developed in consultation
with District staff. The University shall perform literature searches, conduct field
reconnaissance, and familiarize themselves with existing datasets in order to produce a
comprehensive research plan.
The research plan shall:
1) Provide a clear description of all proposed sampling methods and equipment and how
these methods meet objectives.
2) Provide an explanation if these methods deviate from standard techniques.
3) Propose a sampling schedule that demonstrates the amount and type of sampling and
analysis that are expected.
4) Propose sampling locations for field studies/mesocosms that are located in the Upper St.
Johns River Basin or other appropriate District lands, in consultation with District staff.
Task 2. Execute the Research Plan
Task 2.1 – Germination, and early survival and growth experiments
The University shall conduct a greenhouse experiment to assess germination and early survival
of Carolina willow under different soil textures (different proportions of sand, clay, and peat,
which mimic the regional soil gradient) and moisture regimes (mild drought, ambient water,
standing water, and episodic flooding). The University shall use a randomized complete block
design with three levels of soil texture crossed with four levels of moisture and six replicates of
each treatment combination. To conduct this experiment, the University shall collect seeds from
multiple willows at several locations within District lands and pool the seeds into homogeneous
groups.1 The University shall sow 20-30 seeds per pot (20 x 20 x 15 cm) and randomly assign
each group to one of the twelve treatment combinations. The three soil texture treatments shall
be determined in consultation with District staff to represent the range of wetland soils typical of
sites that are either susceptible or resistant to willow invasion.
The University shall follow the protocol of Pezeshki et al. (1998) and water pots according to
one of four schedules:
1) Ambient water = three times weekly, with total application of water equivalent to mean
central Florida annual rainfall, in well-drained (“control”) conditions.
2) Mild drought = twice weekly, with total application of water equivalent to mean central
Florida rainfall minus one standard deviation (as estimated from past 20 years of precipitation
data), in well-drained (“control”) conditions.
3) Standing water = identical watering as treatment #1, but with each pot placed inside a
receptacle to prevent it from draining.
4) Episodic flooding, pots prevented from draining for two-week periods three times each
summer, to simulate the effects of flooding caused by tropical storms and hurricanes.
1 To
quantify variation in seed viability among trees, the University shall place 20 seeds per source willow in
individual Petri dishes under controlled conditions in a growth chamber.
Each of these twelve treatment combinations shall be replicated in each of six spatial blocks, for
a total of 72 pots (1,440-2,160 willow seeds required). The University shall determine the
number (and timing) of seeds germinated at the end of every month using ANOVA for a
randomized complete block design and life table analyses.
The University will also complete two other related experiments on seedling and cutting survival
and growth under different soil textures (different proportions of sand, clay, and peat, which
mimic the regional soil gradient), moisture regimes (mild drought, ambient water, standing
water, and episodic flooding) and nutrients. To conduct this experiment, the University shall
collect seeds and cuttings from multiple willows at several locations within District lands and
pool the seeds and the cuttings (independently) into homogeneous groups. These seeds will be
germinated in a growth chamber and the seedlings (<5 days after germination) transplanted to
pots. The cuttings will be planted temporarily in pots with moist soil to favor rooting and (<5
days after rooting) transplanted to pots. The University shall transplant 3-5 seedlings (or rooted
cuttings) per pot (20 x 20 x 15 cm) and randomly assign each group to one of the eighteen
treatment combinations. The three soil texture treatments shall be determined in consultation
with District staff to represent the range of wetland soils typical of sites that are either
susceptible or resistant to willow invasion. The University shall use a randomized design with
three levels of soil texture crossed with six nutrient treatments (independently for cuttings and
seedlings).
The University shall randomly assign pots in each spatial block to one of six nutrient treatments:
1) ambient nutrients (i.e., those in well water)
2) enhanced N (ambient + 10 %)
3) enhanced P
4) enhanced N & P
5) enhanced micronutrients
6) enhanced N, P & micronutrients.
Exact nutrient concentrations and delivery methods shall be established in conjunction with
District staff to best suit local conditions.
The University shall superimpose soil moisture treatments to the previous designs using a crossover design (Mead 1988), where soil moisture treatments are applied in sequence to each pot, the
sequence being different for different pots. Soil moisture shall be rotated monthly, with each pot
provided with each soil moisture treatment once during the experiment.
Task 2.2 – Willow Transplantation (John)
The University shall conduct a manipulative field experiments (sensu Diamond 1986) that
evaluates seedling survival under contrasting competitive neighborhoods. The University shall
quantify competitive interactions between willow seedlings and the dominant clonal grasses and
shrubs under open (e.g., herbaceous wetland) and shaded (e.g., wetland/upland ecotone)
conditions. The University shall pair transplanted willow seedlings (n = 50 per treatment) in
combination with common grasses and shrubs, with the exact species determined based on the
long-term demographic study described below. Treatments shall include a willow seedling
planted:
(1) without neighbors in a 30 cm radius within a tree gap > 1 m2
(2) within a circular plot with grass cover >50 % and no shrubs closer than 50 cm
(3) within a circular plot with grass cover >50 % and at least one shrub or tree closer than
40 cm
(4) within a circular plot with grass cover <50 % and a shrub or tree closer than 40 cm
This information shall be combined with direct evaluation of the habitat characteristics around
naturally established willow seedlings currently invading different habitats. The University shall
describe species composition, amount of bare ground within a circular plot (30 cm diameter)
centered in focal willows, and random points. The University shall estimate willow occurrence
using the random points and willow individual growth and mortality after eight months as a
function of grass cover and tree presence. The University shall measure shrub canopy cover and
tree diameter of woody individuals closer than 2 m from focal willow plants and the random
points. The University also shall measure environmental characteristics such as soil nutrients (P
and N), organic matter, soil pH, soil moisture, etc. at each site or plot.
At the end of experiment, the University shall harvest the aboveground biomass of willow
transplants and dry and weigh them, and calculate the Relative Neighbor Effect (Armas et al.
2004) to compare plant interactions among treatments. Willow stumps shall be treated (either
mechanically or chemically) to prevent coppicing and regrowth.
Task 2.3 – Fire Response
The University shall use a natural experiment (sensu Diamond 1986) to assess responses of
willow to fire. Choosing sampling sites in consultation with District staff, the University shall
regress willow density and biomass as a function of several indicators of local disturbance,
including amount of bare ground, number of weedy neighbor species, local fire history, and
evidence of human activity. The University shall take advantage of prescribed burns conducted
by District staff during Year 1 to quantify pre- and post-fire conditions of willow responses (e.g.,
seedling and adult survival and growth, plus reproduction) and use them to plan a BACI
(Before/After Control/Impacted) experiment for Years 2 & 3.
Task 2.4 – Willow Life History (Pedro)
The University shall evaluate rates of reproduction, individual growth, aging, effective shortdistance dispersal, and mortality across different regional habitats, selected in consultation with
District staff. For this long-term demographic study, the University shall sample 60-100
randomly-selected individuals stratified by size and reproductive condition across 3-5 different
habitats. The University shall mark willows and measure height, basal diameter, and plant cover,
and estimate number of flowers, and fruit and seed production. The University shall describe
their immediate neighborhoods, including percent open ground, grass and shrub cover, and
number or trees. The University shall revisit marked plants annually as part of a long-term
demographic study (3 years) to estimate rates of individual growth, reproduction, and mortality
in different habitats. The University shall compare these estimates with those obtained from
greenhouse experiments, to quantify how they differ from those observed in greenhouse trials.
The University shall estimate seedling recruitment around established plants with different
densities. The University shall pay special attention to potential interesting observations on
limiting interactions with pollinators, seed predators, and herbivores that should be explored in
future years.
The University shall use standard dendrochronology and allometric techniques to determine
whether growth rings, basal diameter, number of nodes or some other measure reflects
differences in age structure and growth rates among different willow populations. The
University shall empirically test the hypothesis that annual growth rings may be associated with
the winter dry and summer wet seasons in Florida. Briefly, the University shall use stepwise
discriminant function analysis to identify the smallest reliable set of nondestructive willow traits
(e.g., basal area, number of branching nodes, annular ring counts) predictive of age and growth
rates. The University shall use standard methods (Cook and Kairiūkštis 1990) and sample 10-20
willows of various sizes and growth forms at each of the long-term demographic study sites, for
a total sample size of 30-100 individuals. This sample size shall detect a statistically significant
pairwise correlation of r = 0.25-0.36, which approaches the lower limit of biological importance
(R2 = 6-13%) at α = 0.05.
Task 2.5 – Spatial Analysis of Willow Distribution
The University shall characterize the general distribution of willow populations in the St. Johns
River landscape using GIS, including layers on habitat classified by vegetation, soils, and
hydrological and fire regimes. Combined with detailed information on colonization and
extinction probabilities in different habitats (obtained from these experiments and field
sampling), this landscape component will allow the University to understand the local potential
metapopulation dynamics of willow and identify key opportunities for halting its spread.
Task 2.6 - Demographic Modeling
Information on germination, vegetative reproduction, survival, and mortality shall be compared
to estimates obtained from the long-term demographic and dendrochronology studies to develop
a demographic model (Table 1). The University shall integrate the estimates of vital rates across
different environmental conditions in demographic models (Fig. 1) to estimate vital rate
elasticities (relative population growth change with vital rate change) and population trends.
Task 3.1-3.3. Data Analysis and Final Report
Project data are to be analyzed at the termination of each project element. At the end of the each
year, a final report compiling all data should be supplied and should provide a synthesis of how
each ecological factor contributes to the invasion and persistence of willow in herbaceous
wetlands. All data, reports, and figures shall be submitted in both an electronic form, as well as,
paper copies. The format of these documents will be determined by the District Project Manager
and the University prior to data collection. A final report of journal quality shall be provided.
This report will likely contain material for two or more individual manuscripts but shall be
presented as a synthesis report.
IV. TIME FRAMES AND SUMMARY OF TASKS
YEAR 1
Quarter Months
1st
Oct – Dec,
2008
2nd
Jan – Mar,
2009
3rd
Apr – Jun,
2009
4th
Jul – Sep,
2009
Tasks accomplished
Initiate and complete Task 1 (Finalize research plan)
Initiate Task 2.1 (Germination experiment)
Initiate Task 2.4 (Life history)
Continue Task 2.1 (Germination experiment)
Initiate Task 2.2 (Willow transplantation)
Initiate Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.4 (Life history)
Complete Tasks 2.1 & 2.2 (Germination experiment & Willow
transplantation)
Complete Task 3.1 (Data analysis and final report, Year1)
YEAR 2
Quarter Months
1st
Oct – Dec,
2009
nd
2
Jan – Mar,
2010
3rd
Apr – Jun,
2010
4th
Jul – Sep,
2010
Tasks accomplished
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Initiate Task 2.5 (Spatial analysis of willow distribution)
Initiate Task 2.2 (2nd iteration, Willow transplantation)
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.5 (Spatial analysis of willow distribution)
Complete Task 2.2 (2nd iteration, Willow transplantation)
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.5 (Spatial analysis of willow distribution)
Complete Task 3.2 (Data analysis and final report, Year2)
YEAR 3
Quarter Months
1st
Oct – Dec,
2010
2nd
Jan – Mar,
2011
3rd
Apr – Jun,
2011
4th
Jul – Sep,
2011
Tasks accomplished
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.5 (Spatial analysis of willow distribution)
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.5 (Spatial analysis of willow distribution)
Initiate Task 2.6 (Demographic modeling)
Continue Task 2.3 (Fire response)
Continue Task 2.4 (Life history)
Continue Task 2.5 (Spatial analysis of willow distribution)
Continue Task 2.6 (Demographic modeling)
Complete Task 2.3 (Fire response)
Complete Task 2.4 (Life history)
Complete Task 2.5 (Spatial Analysis of willow distribution)
Complete Task 2.6 (Demographic modeling)
Complete Task 3.3 (Data analysis and final report, Year3)
V. DELIVERABLES AND BUDGET
All data (copies of field data sheets, electronic copies of datasets and digital photographs) shall
be sent to the District’s project manager within two weeks after the end of each month. A status
report shall be submitted via email at the same time discussing progress with sampling and
experiments, improvements to research protocols, and notable observations. Digital
photographic documentation of the on-going research (e.g. germinated seedlings, mesocosm setup, field specimens, field/laboratory methodology) shall be supplied as they are collected and as
a final collection submitted on a CD Rom. All sampling shall be completed, all data compiled,
proofread and crosschecked for validity and transmitted, and a final report submitted to the
District’s project manager by the deliverable date.
The budget for this project is currently $50,000 for the first year (October 1, 2008 – September
30, 2009) with similar funding levels anticipated for additional years. Funding levels for
additional years are contingent upon funding availability. Funds are available in the account
named “Scientific Research & Analysis” and account number #60-42-55-6350-3422-04001.
Invoices shall be filed on a percentage of task complete basis. A retainage of 10% will be
withheld from each invoice until the final report is accepted and the project is complete for that
fiscal year.
YEAR 1
Task
Deliverable due
Task 1: Finalize Research Plan
December 1, 2008
Task 2.1: Germination experiment Monthly progress reports
Jan – Aug, 2009
Task 2.2: Willow transplantation Monthly progress reports
Apr – Aug, 2009
Task 2.3: Fire response
Monthly progress reports
Jan – Aug, 2009
Task 2.4: Life history
Monthly progress reports,
Jan – Aug, 2009
Task 3.1: Data Analysis &
Final Report due Sep 30,
Reporting
2009
Estimated cost
$1,000
$17,500
$8,500
$3,500
$11,500
$8,000
Total = $50,000
YEAR 2
Task
Task 2.2: Willow transplantation
(2nd iteration)
Task 2.3: Fire response
Task 2.4: Life history
Task 2.5: Spatial analysis of
willow distribution
Task 3.2: Data Analysis &
Reporting
Deliverable due
Monthly progress reports
Apr 2010 – Sep 2010
Monthly progress reports
Oct 2009 – Sep 2010
Monthly progress reports,
Oct 2009 – Sep 2010
Monthly progress reports,
Jan 2010 – Sep 2010
Final Report due Sept 30,
2010
Estimated cost
$8,500
Deliverable due
Monthly progress reports
Oct 2010 – Sep 2011
Monthly progress reports,
Oct 2010 – Sep 2011
Monthly progress reports,
Oct 2010 – Sep 2011
Monthly progress reports,
Jan 2011 – Sep 2011
Final Report due Sept 30,
2011
Estimated cost
$9,500
$9,500
$10,500
$13,500
$8,000
Total = $50,000
YEAR 3
Task
Task 2.3: Fire response
Task 2.4: Life history
Task 2.5: Spatial analysis of
willow distribution
Task 2.6: Demographic Modeling
Task 3.3: Data Analysis &
Reporting
$10,500
$13,500
$8,500
$8,000
Total = $50,000
Literature cited
Armas, C., R. Ordiales, and F. I. Pugnaire. 2004. Measuring plant interactions: A new
comparative index. Ecology 85:2682-2686.
Cook, E., and L. Kairiūkštis. 1990. Methods of Dendrochronology: Applications in the
Environmental Sciences. Springer.
Diamond, J. 1986. Overview: Laboratory experiments, field experiments, and natural
experiments. Pages 3-22 in J. Diamond and T. J. Case, editors. Community Ecology.
Harper and Row, New York, New York, USA.
Mead, R. 1988. The Design of Experiments: Statistical Principles for Practical Application.
Cambridge University Press, New York.
Pezeshki, R., P.H. Anderson, and F.D. Shields. 1998. Effects of soil moisture regimes on growth
and survival of black willows (Salix nigra) posts (cuttings). Wetlands 18: 460-470.