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Initial Response of Soil and Understory
Vegetation to a Simulated Fuelwood Cut of
a Pinyon-Juniper Woodland in the Santa Fe
National Forest
Samuel R. Loftin
Abstract-The Santa Fe National Forest, Espanola Ranger District, the Bandelier National Monument, and the Rocky Mountain
Research Station are evaluating a treatment designed to stabilize
the soils and increase the abundance- of herbaceous plants in
degraded pinyon-juniper ecosystems. The treatment removed all
pinyon less than 8 inches in diameter and all juniper. The trees
were felled, lopped, and the wood and limbs (slash) were scattered
across the site. Cover of herbaceous vegetation nearly doubled on
the treated site after one growing season and more than doubled
after two growing seasons. Significantly higher plant species richness was recorded on the treated site. The preliminary results
indicate that this could be an effective pretreatment to the reintroduction of fire.
Many grasslands in the western United States are dependent upon periodic fire to maintain their productivity and
stability (Clements 1936). The absence of fire could lead to
the succession of grasslands to woodlands or desertscrub
(Dick-Peddie 1993). Throughout the western United States,
a combination of widespread livestock grazing and periodic
drought has promoted woody plant expansion and dominance in areas believed to have been predominantly grassland (Burkhardt and Tisdale 1976; Buckman and Wolters
1986; Grover and Musick 1990; Miller and others 1994).
Livestock can reduce fine fuel loads and alter fire frequencies or eliminate fire completely. Periodic drought can select
for deep-rooted woody species over shallow-rooted grasses
and forbs (Schlesinger and others 1990).
Regardless of the extent of grasslands that have been
replaced by pinyon-juniper or juniper woodlands, the type
conversion of grassland to woodlands is not necessarily
considered to be a problem. The expansion and contraction
of woodland and grassland boundaries is a natural process
that has been occurring across this landscape for thousands
ofyears (Betancourt 1986; Jameson 1986; Miller and Wigand
1994; Van Devender and others 1984). The problem, as
commonly perceived, is the increase in surface runoff and
soil erosion that often accompanies a loss of herbaceous
plant cover. Surface runoff and soil erosion remove the two
In: Monsen, Stephen B.; Stevens, Richard, comps. 1999. Proceedings:
ecology and management of pinyon-juniper communities within the Interior
West; 1997 September 15-18; Provo, UT. Proc. RMRS-P-9. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research
Station.
Samuel R. Loftin is a Research Plant Ecologist, Rocky Mountain Research
Station, 2205 Columbia, SE, Albuquerque, NM 87106.
USDA Forest Service Proceedings RMRS-P-9. 1999
resources necessary for maintaining the stability and productivity of these ecosystems, water and soil. Once the soil
is gone, the system cannot support a grassland and the
question of whether grasslands or woodlands belong on the
site becomes academic.
Objectives
The objectives ofthis research are to evaluate methods for
restoring properly functioning eda phic and hydrologic processes, which preserve our options for future land management. More specifically, we hope to stabilize the soil, increase water availability, and increase herbaceous plant
abundance, which should further stabilize the soil. This
should initiate a positive-feedback cycle of increasing stability and productivity and disrupt the present cycle of increasing degradation. We plan to re-introduce fire back into
this system, initially as a restoration treatment to control
tree seedlings. Ultimately, fire must be used as a management tool to maintain the structure and function of the
grassland component of this ecosystem.
Approach
The thinning treatment should affect several processes
that could lead to increased soil stability, plant water availability, and herbaceous plant abundance. Removing trees
will result in a reduction in competition for water between
trees and herbaceous plants. The slash mulch should increase soil surface roughness and reduce runoff, thereby
increasing infiltration and water availability. The mulch
will shade the soil and reduce air flow, thereby reducing
evaporative loss. The mulch will reduce raindrop impact on
bare soils which will reduce the potential for erosion. The
mulch will insulate bare soils in the winter, thereby inhibiting frost heave which loosens the soil and also damages
seedling plants. Finally, the slash mulch will inhibit grazing
by large ungulates that prefer not to nose around in the
piles of sticks and twigs.
The trees were cut with chain saws, rather than chaining,
cabling, or pushing which requires the use of heavy equipment. This method reduces the disturbance associated with
the treatment and reduces the potential for soil erosion and
establishment of invasive weeds. This treatment can be
implemented as a fuelwood sale which would reduce labor
costs for the management agency and provide a resource for
the public. This type of fine-scale management also allows
managers to tailor the treatment to the desired future
condition for the site.
311
Methods _ _ _ _ _ _ _ _ __
(number of species) can be extracted from the CSA data.
Vegetation was sampled in Fall 1994 (pretreatment), Fall
1995 (one growing season post-treatment) and Fall 1996
(two growing seasons post-treatment).
Site Description
The study site is located in northcentral New Mexico, on
the Santa Fe National Forest, Espanola Ranger District.
The site is approximately 25 ha on a south-facing slope
which, previous to treatment, supported a dense stand of
pinyon (Pinus edulis) and juniper (Juniperus monosperma)
trees. Dominant herbaceous plant species incl ude blue grama
(Bouteloua gracilis), mountain muhly (Muhlenbergia
montana), muttongrass (Poa fendleriana), tarragon (Artemisia dracunculus), and pinque (Hymenoxys richardsonii).
Soils on the site are classified as fine-loamy to loamyskeletal, mixed mesic Typic Haplustalf (USDA 1993).
Statistical Analysis
Due to the lack of treatment replication, this study must
be considered a case study, the results of which are not to be
extrapolated beyond the spatial and temporal limits of the
data collected. The effect of thinning was tested by comparing post-treatment conditions on the treated plots to any
change on the control plots for comparable time periods. A
repeated measures analysis was utilized with thinned vs.
control included as a treatment factor, post-treatment
years as repeated measures, and the pre-treatment year
(1994) as a covariate. In some instances, the effect of thinning was not the same for both post-treatment years (that is,
significant interaction between treatment and time). In
these instances, significance ofthinning for individ ual years
was assessed by applying a t-test to the change from pretreatment conditions for each treatment for a particular year.
Similarly, significance of potential time trends was assessed
by applying a t-test to the change from pre-treatment conditions for each post-treatment year within a particular treatment category. Type I error for these sets of t-tests was
maintained by applying a Bonferroni adjustment to significance levels of individual tests (Miller 1981). All statistical
analyses were conducted using the Statistical Software
for the Social Sciences (SPSS Inc. 1990).
Treatment
The treatment used in this study was removal of all
pinyon less than 8" diameter at breast height, and all
juniper. Trees were cut at ground level, limbed and lopped.
The slash was distributed evenly across the surface of the
site. The treatment was conducted in April, 1995 by personnel from the Espanola Ranger District.
Experimental Design
There was no replication of treatments in this experimental design. Each treatment (thinned and control) was
approximately 10-15 ha. The treatments were positioned
end to end along a south-facing slope. Each treatment was
divided into five blocks. Within each block there are three,
100 m transects, one for vegetation sampling, one for soil
sampling, and one for soil erosion estimates. Only the
vegetation analysis will be discussed in this paper.
The vegetation was sampled using the Community Structure Analysis (CSA) technique of Pase (1981). This sampling techniq ue generates estima tes of cover, frequency, and
density for sampled plant species. Only cover estimates will
be presented in this paper. Estimates of species richness
Results _ _ _ _ _ _ _ _ _ _ __
Analysis of cover shows significant treatment effects on
all cover types (table 1). Tree cover and bare soil both
decreased as a direct result of the thinning treatment and
there was no significant (P::; 0.05) difference between posttreatment years. Total herbaceous cover was significantly
greater on the thinned area and increased significantly
from Fall 1995 to Fall 1996. Forb cover and grass cover
Table 1-Cover (%) means (N = 5) and standard errors for various cover types on control and thinned
areas for Fall 1994a (pretreatment), Fall 1995, and Fall 1996.
Sampling Period
94
Cover Type
Tree
Total
Herbaceous
Forb
Grass
Bare Soil
Treatment
Control
Thinned
Control
Thinned
Control
Thinned
Control
Thinned
Control
Thinned
x
36.4
25.5
7.1
6.8
1.4
1.8
5.7
5.0
36.0
42.9
96
95
SE
3.9
2.6
1.1
0.5
0.3
0.3
1.1
0.3
3.6
2.7
x
39.9ax
7.9bx
6.9ax
12.2bx
1.5ax
4.9bx
5.4ax
7.3bx
35.6ax
27.4bx
SE
5.2
3.0
1.1
0.8
0.5
0.5
0.8
0.5
2.0
0.7
x
39.2ax
9.2bx
9.2ax
22.6by
1.5ax
8.6bx
7.7ay
14.0by
35.7ax
21.7bx
SE
5.7
3.1
2.2
2.1
0.5
1.2
2.2
1.0
2.7
1.3
apretreatment means are presented for the reader's information; however, they were used as covariates in the
repeated measures analysis and are not included in the multiple t-test evaluation of means. Means followed by the same
letter (a,b,c), within a cover type and year, are not significantly different (P ~ 0.05). Means followed by the same letter
(x,Y,z), within a cover type and treatment, are not significantly different.
312
USDA Forest Service Proceedings RMRS-P-9. 1999
Table 2-Species richness means (N = 5) and standard errors for various vegetation categories on
control and thinned areas for Fall 1994a (pretreatment), Fall 1995, and Fall 1996.
Sampling Period
94
Category
All
Species
Forb
Species
Grass
Species
Treatment
Control
Thinned
Control
Thinned
Control
Thinned
x
19.6
19.4
9.4
10.0
6.0
5.0
96
95
SE
1.8
0.9
1.2
0.6
0.8
0.5
x
17.2ax
22.0bx
8.8ax
13.0bx
4.6ax
5.4bx
SE
1.3
1.3
0.9
0.7
0.7
0.2
x
23.0ay
29.0by
13.8ay
16.8by
5.6ay
7.4by
SE
1.7
1.09
1.4
1.2
0.4
0.6
apretreatment means are presented forthe reader's information; however, they were used as covariates in the repeated
measures analysis and are not included in the multiple t-test evaluation of means. Means followed by the same letter
(a.'b~c), within a cover type and year, are not significantly different (P ~ 0.05). Means followed by the same letter (x,y,z),
within a cover type and treatment, are not significantly different.
(components of total herbaceous cover) both increased significantly following the thinning treatment but only grass
cover had a significant time effect.
Significant thinning and time effects were recorded for
species richness for all vegetation categories (table 2).
Discussion -------------------------------The treatment achieved the immediate goals of reducing
tree cover and bare soil cover. Total herbaceous plant
cover on the treated area was twice that on the control area
after one growing season and almost 2.5 x greater than
controls after two growing seasons. Both forb and grass
cover (the two components of total herbaceous cover) increased as a result of the treatment. Clearly, the objective of
increasing herbaceous plant abundance was realized after
only two growing seasons.
The concept of biodiversity is important with respect to
species preservation and ecosystem stability (Tilman 1996;
Tilman and others 1996). Although species richness is not
the best estimator of biodiversity response to disturbance
(Barbour and others 1987), it is the only index that can be
generated from the CSA data. The response observed in
this study was probably due to a combination of climatic
effects (increased rainfall may have resulted in more recorded species on both sites), and possibly to an improvement of our taxonomic skills. Most ofthe response in species
richness is due to an increase in forb species. The number of
grass species has remained relatively constant throughout
the study.
The next phase of the project is to re-introduce fire back
into the treated area. The objective ofthe initial (restoration)
fire will be to control the resprouting stumps and abundant
seedling trees that were released from competition with the
mature trees. There are often 15 to 20 seedlings existing
under the canopy of a mature tree. If this cohort is not
controlled the future density of trees on this site could be
many times greater than the pretreatment density. The
timing of the first burn is somewhat critical. Ifwe burn too
soon, the fuel loads from the slash and herbaceous plants
could be high enough to scorch and sterilize soils. However,
if we wait too long to burn, the seedling trees and resprouting
USDA Forest Service Proceedings RMRS-P-9. 1999
stumps could get too big to be effectively controlled by the
fire. Prescribed fire is most effective 3 to 5 years following
mechanical treatments to control redberry or blueberry
juniper resprouts in Texas (Erramouspe 1994). We anticipate conducting the initial prescribed fire sometime between 3 to 5 years post-treatment.
Conclusions -------------------------------The treatment method of hand-thinning trees in a degraded pinyon -j uni per woodland significan tly increased herbaceous plant abundance (without seeding) within 2 years at
this site. Additionally, the treatment has significantly increased species richness. Although this method may not be
as efficient at removing trees as techniques involving heavy
equipment, it is much less destructive, and much more
appropriate for sensitive areas. The treatment has initiated
the process of ecosystem restoration. We plan to re-introd uce
fire as a means to complete the restoration of the site and
maintain the functional processes of a stable and productive
grassland ecosystem.
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