Relationship Between Small Mammals And Habitat On Huntington Wildlife Forest

Shannon L. Strusz

Peromyscus spp. in leaf litter.

Introduction
Small mammals have integral and diverse ecological roles that impact the structure and function of forested ecosystems. Many function as predators, prey, and carriers of disease, dispersers of seeds and nuts, and/or foragers of agricultural crops. Habitat changes occur naturally and by human activities. However, the relationship between small mammals and their habitat is poorly understood. The response of small mammals a change in habitat is crucial in maintaining the integrity of the ecosystem, while still allowing for economical resource management.

The purposes of this study were to (1) evaluate changes in small mammal populations from 1992-2002 on HWF ALTEMP (Adirondack Long-Term Ecological Monitoring Project) sites, (2) examine changes in habitat between 1988 and 2002, and (3) relate certain habitat changes and aspects to small mammal abundances in 2002.

Methods

In 1988, a habitat assessment occurred on small mammal ALTEMP trapping sites. During this study, 24 total permanent habitat assessment sites (ALTEMP #25) were established on ALTEMP small mammal grids within Hare Area (HA), Maple Sale (MS), and Natural Area (NA). The diameter at breast height (DBH) of trees, CWD size classes and decay stages, and number of pieces were evaluated. The percent canopy cover per site, and percent Ground Cover (forb, grass/sedge, woody vegetation) per site were also measured and evaluated in 2002.

Evaluating percent of ground cover.

Small mammal catch per unit effort, CPUE (# animals per 100 trap nights) were calculated from 1992-2002 ALTEMP raw data. T-tests were performed to detect changes in mean DBH of tree species and percent Ground Cover within each site between 1988 and 2002; these variables were compared with small mammal abundances from 1992-2002. Percent canopy cover and CWD number of pieces, size classes, and decay stages from 2002 were compared with small mammal CPUE in 2002.

Woodland jumping mouse in leaf litter.

Results

The CPUE of the short-tailed shrew was lowest in the HA, and very similar within the MS and NA. These small mammals depicted "cyclical" CPUE, changing from high to low abundances every year within each site. CPUE varied from 0 to 4.1 in the HA, 0 to 9.2 in the NA, and 0 to 9.4 in the MS. The woodland jumping mouse exhibited fluctuations in CPUE during some years within each study site. The CPUE varied from 0 to 6.1 in the HA, 0 to 1.5 in the NA, and 0 to 2.3 in the MS respectively. These animals were found in highest abundances within the HA, while present in similar abundances in both the MS and NA. Peromyscus spp. displayed "cyclical" CPUE, alternating in each site during identical years. CPUE ranged from 0 to 4.9 in the HA, 0 to 5.1 in the NA, and 0.5 to 3.8 in the MS respectively from 1992-2002. Peromyscus spp. were more abundant in the HA during the early 1990's, although recently they were more abundant within the MS and NA. The eastern chipmunk showed no cycle in abundance over time in each site. The CPUE ranged from 0 to 34.9 in the HA, 3.9 to 26 in the NA, and 5.9 to 55.4 in the MS respectively. The graph shows that the CPUE was among highest for eastern chipmunks within the MS, while they were similar for both the HA and NA.

A shrew that has just been released.

The mean DBH of American beech increased from 2.4 ± 3.4 to 8.9 ± 8.1cm, striped maple increased 1.7 ± 1.3 to 4.1 ± 1.9 cm, and yellow birch increased from 1.7 ± 0.7 to 6.1 ± 2.7 cm DBH in the MS. In the NA, the American beech decreased from 25.4 ± 16.5 to 8.2 ± 6.5 cm, and sugar maple decreased from 59.8 ± 8.1 to 30.8 ± 19.4 cm in mean DBH. The mean percent of Ground Cover decreased significantly from 27.31 to 2.67 percent in the MS. The mean percent canopy cover measured in 2002 was 93.8 % in the HA and MS, and the NA was 98.1 %. Table 1 shows the number of pieces of CWD, size class and decay stage in 2002. Small mammal species displayed varying CPUE in relation to CWD (Figure 1).

Table 1. Min/Mean/Max of CWD Size Class and Decay Stages on Huntington Wildlife Forest in 2002.

Figure 1. Number of Coarse Woody Debris (CWD) pieces compared with Small Mammal Catch per unit effort (CPUE) on HWF in 2002.

Discussion

The small mammal cycles in CPUE may have resulted from food abundance, sunspots, climate, weather, social changes within an animal population, territoriality, predation and change in habitat; justifications are very controversial in the literature.

The mean DBH and abundance of some tree species changed over time; the majority of these changes were expected to occur within stands that were most recently harvested. American beech showed opposing results in NA and MS, possibly resulting from prevalence of beech bark disease in NA verses MS (not documented on HWF), recent harvest in MS, small beech trees surviving competition, thus increasing in DBH in MS, and/or a decline in # trees in NA (old-growth forest) due to maximum age reached. Eastern chipmunk declines in CPUE calculated in 2002 could be indirectly related to small mean DBH size of American beech in MS, and declining American beech DBH size in NA; however, no direct relationship was apparent.

Chipmunk captured in Tomahawk live trap.

DeGraaf et al. (1989) noted that Peromyscus spp. require 16-30% canopy cover; all study areas on HWF had canopy cover >93%, much more than what DeGraaf et al. (1989) recommended for Peromyscus spp. Herbaceous ground cover is important to small mammals; Peromyscus spp. and woodland jumping mice especially use dense herbaceous cover to escape predation, and as a food source or nesting material. DeGraaf et al. (1989) suggest that Peromyscus spp. and woodland jumping mice require >75 % of forb, grass, and woody vegetation cover; study sites on HWF contained <18% of ground cover, nowhere near the recommended percentages. Thus, these results may support DeGraaf et al. (1989) suggestion, and justify the low Peromyscus spp. and woodland jumping mice abundances in 2002.

Evaluating decay stage.

CWD functions as essential habitat to small mammals. CWD provides pathways for travel, nesting and burrowing sites, protective cover, and acts as a source of foraging habitat. However, no apparent relationships with log or stump data to any of the small mammal species were detected; there may be a sufficient amount of different CWD sizes and decay stages available to small mammals. The relationship between small mammal abundances and CWD are often very difficult to distinguish, as this study demonstrated.

Conclusions

Small mammal CPUE cycles suggest that other aspects of the ecosystem must be influencing small mammal abundance. I recommend that when relating habitat change over time, a much longer time period of small mammal data should be implemented. It would be useful to further investigate microclimate characteristics, such as soil pH and moisture, temperature, pH, and moisture of CWD, and slope of the particular study area in relation with habitat change compared with small mammals.

Literature Cited:
DeGraaf, R. M., M. Yamasaki, W. B. Leak, and J. W. Lanier. 1989. New England wildlife: management of forested habitats. U.S. Forest Service General Technical Report NE-144.

Contact info:
For further information on any of these projects, you can contact:
Adirondack Ecological Center- aechwf@esf.edu

About the author:
Shannon L. Strusz is currently a senior undergraduate student at the SUNY College of Environmental Science and Forestry. She has recently been inducted President of the Student Chapter of The Wildlife Society at SUNY-ESF, is a calculus T.A., and enjoys mountain biking, hiking, playing the guitar, and spending time with her family and friends. Shannon currently spent 12 weeks on HWF in the Adirondack Mountains of New York conducting research on habitat and small mammal relationships, and contributed assistance in deer trapping, radio telemetry, small mammal trapping, and amphibian sampling. She would like to thank Leah Burke for her company and assistance while working together at the AEC on HWF this summer, and Stacy McNulty and the rest of the AEC staff for all of their help, suggestions, and good humor this summer.