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Commercial Fuelwood Harvesting Affects on
Small Mammal Habitats in Central Arizona
William H. Kruse
Abstract-In a central Arizona fuelwood harvest area, 75 percent
of the overstory was cut in a commercial harvest, resulting in large
quantities of residual logging debris that altered habitat for many
wildlife species. Small mammals have intricate roles in ecosystem
function, and current fuelwood management practices have paradoxical affects on small mammal habitats. In a small mammal
study, no differences in total animals capt,ured were detected among
treatment plots. Immediately following overs tory reduction or removal in 1992 and 1993, differences among species ca ptures, s pecifically deer mouse, increased significantly. The increased capture
rate remained significant throughout the remainder of the study.
Pinyon mouse captures declined significantly immediately following treatments, but were not detectablydifferent from pretreatment
levels a year later.
Commercial fuelwood harvesting generates greater and
more concentrated slash and has more affect on microsite
conditions than noncommercial fuelwood cutting. This has
prompted some central Arizona USDA Forest Service Ranger
Districts to assess the effects of commercial fuelwood removal and slash disposal, particularly by burning. Specifically, removal of slash habitat through burning is a concern.
Fortunately, commercial harvest permits, however, can provide detailed slash management directions to meet specific
management objectives. Burning is usually not performed
by the fuelwood permit holder but instead is included in
Forest Service management plans.
Fuelwood removal and slash management also affects
microsite nutrient cycling, miderstory production (specifically protecting forages from large ungulate grazing), and
regeneration of overstory species. Small mammal populations are also affected by removal of overstory, understory
composition and structure change, and slash accumulation
and subsequent manipulation. Basic ecological information
is needed to support current harvesting plans (Gottfried
1987). The least understood management option has been
slash disposition (Severson 1986, Baker and Frischknecht
1973).
Retention or removal of slash provides or eliminates
specific habitat characteristics for certain small mammals.
In addition, retention or removal of slash affects the potential protective cover for emerging new plants. Slash removal
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.
William H. Kruse is Range Scientist (retired) USDA Forest Service,
Rocky Mountain Research Station. The Southwest Forest Sciences Complex,
2500 S. Pine Knoll Dr. Flagstaff, AZ 86001.
USDA Forest Service Proceedings RMRS-P-9. 1999
by burning affects the newly formed slash habitat for small
mammals and plants and also reorganizes the nutrient base
stored in the slash (Harrington 1989, Covington and DeBano
1988). Natural decomposition of residual slash provides a
slower and more complete return of nutrients to the system,
while providing the protective effects of slash. J uni per slash,
unlike pine slash, decomposes at a slower rate.
Small mammal populations are impacted by overstory
disturbances (Turkowski and Reynolds 1970) while on-theground slash causes an increase in abundance of some
rodent species regardless of overstory condition (Severson
1986). Kruse and others (1979) found that when the overstory was removed or reduced, rodents that preferred the
woodland condition were fewer in number than those on the
treated areas.
This small mammal research was part of an effort to study
the effect of nutrient cycling, other wildlife, and wood product management on soil, water, tree, and range resources in
pinyon-juniper woodlands. This paper discusses the effects
of commercial fuelwood harvesting in an old-growth or late
seral pinyon-juniper woodland on small mammal populations in central Arizona.
Study Area _ _ _ _ _ _ _ __
The Heber Ranger District, Apache-Sitgreaves National
Forest in central Arizona was the study-site area. Average
tree basal area (diameter measured at root crown) was
23.2 ± 5.4 m 2/ha, which produced 35.3 ± 12.7 m 3/ha of fuelwood (Kruse and Perry 1995). One-seed juniper (Juniperus
monosperma) was the dominant species (54 percent). The
second most dominant tree (25 percent) was Colorado pinyon (Pinus edulis), followed by alligator j uni per (J. deppeana)
(13 percent). Ponderosa pine (Pinus ponderosa) occasionally
occurred on moist sites (8 percent). Mean pretreatment
canopy cover was approximately 40 percent, while the mean
annual herbaceous and woody plant potential productivity
was approximately 562 kg/ha.
The study area is relatively flat, dissected by several small
ephemeral drainages. Elevations are between 2,000 and
2,060 m. The primary soil subgroups, derived from limestone, are Lithic Ustochrepts, Udic Haplustalfs, and Typic
Eutroboralfs. The mean annual precipitation is between
34 and 46 cm.
Methods
Field Methods
The study area consisted of 33 units, 4 ha in size. Three
units were treated with silvicultural prescriptions. Thirty
4 ha study units were grouped into five blocks representing
215
Figure 1-Typical overstory, preharvest conditions of
late seral old-growth pinyon- juniper woodland at Heber/
Mud Tank small mammal study area.
Figure 3-Type conversion. Slash accumulation but
not burned following harvest of commercial fuelwood.
Noncommercial stems cut and also remain.
six overstory/slash treatments. Sixteen of the 30 were randomly selected for the small mammal study. Four of the
6 overstory/slash treatments were replicated in the 16 units
(Kruse 1995).
Trapping occurred on 4 overstory treatments: (1) controls,
where the units were untreated (fig. 1); (2) burned, to
simulate a forest fire (fig. 2); (3) type conversion, where
fuelwood was harvested, the non-commercial residual trees
cut, but slash was not burned (fig. 3); (4) type conversion,
where fuelwood was harvested, residual trees cut, and slash
burned (fig. 4). Type conversion is clearcutting to convert a
woodland to grassland. The two overstory treatments not
included were the silvicultural treatments and the commercial harvest where the noncommercial stems were left uncut
as advanced regeneration. Small mammal trapping was
conducted during July and August from 1990 through
1996. Before harvest, downed woody fuel was estimated at
3.15 mtJha (Kruse and Perry 1995). Post harvest slash
accumulation was estimated at 55.71 mtlha (fig. 3).
Treatments were assigned randomly and were not necessarily contiguous; roads or drainage channels could separate
units within a given block. Harvesting began during fall!
winter of 1991 and continued for 24 months. Burning commenced when the slash was at least 2 years old. Treatment
schedules are in Kruse (1995).
A 100 m 2 trapping grid was located in the center of
each unit. 8 x 10 x 25 cm Sherman live trap was placed at
each grid point, 10 m x 10 m apart. At alternate points, a
10 x 12 x 40 cm Sherman live trap was placed near the
smaller one. The bait was a mixture of chicken scratch and
rolled oats. Each unit was sampled yearly with 150 traps
for 3 nights and 2 days. Physical measurements were taken
and recorded for each animal, then they were toe clipped
Figure 2-Burned standing green
woodland to simulated wildfire for
type conversion (clearcutting to
convert a woodland to grassland).
216
Figure 4-Type conversion. All overstory harvested or
cut, and slash burned.
USDA Forest Service Proceedings RMRS-P-9. 1999
Table 1-Species captured and percent of composition.
Species
Common name
Peromyscus truei
Peromyscus maniculatus
Eutamias dorsalis
Neotoma albigula
Neotoma mexicana
Peromyscus boylei
Sylvi/agus auduboni
Spermophilus variegatus
Neotoma stephensi
Dipodomys ordi
Microtus mexicanus
20
Composition
pinyon mouse
common deer mouse
cliff chipmunk
white-throated wood rat
Mexican wood rat
brush mouse
desert cottontail
rock squirrel
Stephens wood rat
Ord kangaroo rat
Mexican vole
Percent
42
37
9
7
2
2
<1
<1
<1
<1
and released. Recaptures were noted. Relative abundance
and species composition of small mammals live trapped and
released on the study area are in table 1.
Analysis Methods
Replicated study units among 4 blocks were selected
randomly as the experimental design layout (Ludwig and
Reynolds 1988). Blocks were based on similarity of pretreatment overs tory conditions and characteristics. The treatment units included combinations of no burning or cutting,
burning standing green, cutting and no cutting (fig. 1-4).
The small mammal study replicated these 4 treatments in
each of 4 blocks.
The null hypotheses was that small mammal capture
rates did not differ among treatments. Capture differences
80r-------------------------------~
_
Untreated
...............
'1iiiiii"'T~~~t~d"
............. '"
60
12
8
4
0
93
94
95
96
91
90
90 vs 91 P = 1.0
mean 90,91 vs.93 P = < 0.001
mean 90,91 vs.94 P = < 0.001
mean 90,91 vs.95 P = < 0.001
mean 90,91 vs.96 P = 0.004
Figure 6-The deer mouse captures. Captures were
significantly increased immediately following treatments
in 1992-93 (p < .001). and remained higher through the
remainder of the study (p < .004) while the slash habitat
was on the ground aging. Some of the units were burned
before the 95 and 96 trapping periods but it is unclear
whether the burning impacted the deer mouse captures.
among treatments were tested by analysis of variance with
years used as a repeated measure. Significance oftreatment
effects was assessed based on temporal interaction (pre vs.
post treatment) in treatment responses. Comparisons among
treatments, for individual post treatment years were adjusted by Bonferoni correction to maintain Type I error at
0.05. Tests were performed on total captures, deer mouse
captures, and pinyon mouse captures only. The 1992 data
was also omitted from the analyses due to conflicting treatment effects and application.
Results _ _ _ _ _ _ _ _ _ __
40
20
o
16
90
91
93
94
95
90 vs 91 P = 1.0
mean 90,91 vs. 93 P = < 0.001
mean 90,91 vs. 94 P = 0.537
mean 90,91 vs.95 P = 1.0
mean 90,91 vs. 96 P = 1.0
Figure 5-There were no differences in captures between unharvested and to-be- harvested units during the
pre-treatment period (p > .5). Total captures of all species significantly increased immediately following treatment in 1992-1993 (p < .001). but were not detected
again (p > .5).
USDA Forest Service Proceedings RMRS-P-9. 1999
96
Before 1992 harvest treatments, there were no differences
among the unharvested and the to-be-harvested units for
total captures (fig. 5). Although year-to-year differences
occurred, these data demonstrated the homogeneous nature (p = 1.0) of all units in 1990 and 1991. Analysis of post
treatment responses, however, indicated significant treatment effect (F= 7.17, p < 0.001). Following treatment, a
significant difference among treatments in 1993 was demonstrated (F = 5.79, SE 5.47, p < 0.001). Total captures treatment effects were not significant for 1994 (p = 0.536), 1995
(p = 1.0), and 1996 (p = 1.0).
Deer mouse captures on the harvested and the unharvested units (fig. 6) also showed the similarity among all
units before treatment (p = 1.0), and the significant difference between treatments in 1993 (p < 0.001). Unlike total captures, differences for deer mouse captures were significant
for 1994 (p < 0.001), 1995 (p < 0.001), and 1996 (p = 0.004).
Half of the harvested units were burned in 1995 and 1996.
Pretreatment tests on pinyon mouse captures among all
study units were again similar (p = 1.0). Converse to the deer
217
mouse, pinyon mouse captures (fig. 7) significantly reflected
a negative effect following treatment in 1993 (p =0.052). This
negative effect for the pinyon mouse between the harvested
and non-harvested units was not evident in 1994 (p = 0.322)
but was evident in 1995 (p =0.017) and 1996 (p = 0.040). The
1995 and 1996 harvest unit data included some units that
were burned in 1994 and 1996; 1996 was before sampling.
Discussion --------------------------------This study was designed to evaluate fuel wood harvesting
affects on small mammal capture rates following the harvest
of old-growth or late-seral pinyon-juniper woodland overstory. The treatments were 1) overstory removal; 2) creation
of large quantities of slash that was generally lopped and
scattered, although some piling was _done to allow cutting,
loading, and hauling, and 3) eventual slash burning. Data
were insufficient to determine which treatment activity had
the greater affect on the small mammal capture rates.
Therefore, the "treatment" units included overstory removal,
slash deposition, and some were burned. These "treatment"
units were tested against the uncut units.
Although not tested, it appeared that: 1) woodrat (Neotoma
spp.) middens burned; 2) numbers of captures of all species
may have decreased following burning; and 3) captures of
brush mice (Peromyscus boylii) appeared to be greater on
unburned slash units. Initially, both Peromyscus species
responded positively or negatively to the harvest treatment
and some differences continued for the following 3 years.
Half of the harvested units were burned in 1994 and 1995.
Burning standing green, during a wildfire simulation, occurred in 1994 and 1996. The study suggests that overstory
removal and slash accumulation probably had more beneficial effects for the deer mouse, specifically, and to other species
as well. These 2 effects were detrimental to the pinyon
mouse, however, particularly in the year following cutting.
This study corroborates earlier work showing that overstory
is important to the pinyon mouse (Severson 1986). Burning,
which would not have correctea the lack of overstory condition, was of further detriment to the pinyon mouse.
Fewer captures of all species were evident in the latter
3 years that included the burning portion of the study. Tests
between treated and untreated units suggest little significant difference, while treatment effects to the deer mouse still
appear beneficial. Field observations suggest that unburned
units still contained viable woodrat middens and higher
capture numbers for other species such as the cliff chipmunk
(Eutamias dorsalis). Baker and Frischknecht (1973) found
no effect from slash on mice populations, except where it was
windrowed, while Severson (1986) found that treatments
leaving slash benefited woodrats and brush mice following
canopy removal. Therefore, the detrimental burning effects
in this study could have off-set the beneficial effects of the
slash. In addition, slash provided improved site protective
characteristics for plant regeneration and development.
Population densities of small mammals are related to
overstory adjustments and/or slash composition in assessing site productivity and quality. This study contributes to
small mammal and basic ecological information to improve
guidelines for harvesting fuel wood in pinyon -j uni per ecosystems in the Southwestern United States.
218
35
30
............... IMJ ..l)n~~~?:t.~9; ...... .
_
Treated
25
20
15
10
5
o
93
94
90
91
95
96
90 vs 91 P = 1.0
mean 90,91 vs.93 P = 0.052
mean 90,91 vs.94 P = 0.322
mean 90,91 vs.95 P = 0.017
mean 90,91 vs.96 P = 0.040
Figure 7-Pinyon mouse captures. Captures were significantly decreased immediately after treatments were
implemented in 1992-93 (p = .05), but not detectably
lower a year later (p = .32). Lower captures on the
treated units were again apparent in 1995-96 (p < .04).
References __________
Baker, Maurice F. and Neil C. Frischknecht. 1973. Small mammals
increase on recently cleared and seeded juniper rangeland. J.
Range Manage. 26: 101-103.
Covington, W. Wallace and Leonard F. DeBano. 1988. Effects of fire
on pinyon-juniper soils. pp 78-85. In Proceedings: Effects of Fire
in Management of Southwestern Natural Resources. Tucson,
Arizona. Nov. 14-17, 1988.
Gottfried, Gerald J. 1987. Regeneration of pinyon. In: Proceedings-pinyon-juniper conference; 1986 January 13-16; Reno, NV.
Ogden, UT: U.S. Department of Agriculture, Forest Service,
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Harrington, M.G. 1989. Soil nutrient and pinyon seedling response
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on fire and forest meteorology, Maciver, D.C., ed. and others
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USDA Forest Service Proceedings RMRS-P-9. 1999