UP Project |
Small Mammal Dynamics in Pinyon-Juniper Treatments of the Dry Creek/ Spring Creek Watersheds on the Uncompahgre Plateau, Colorado
Principle Investigators
Cynthia Rebar, Ph.D., Dept. of Biology and Health Services
Denise Stetson, B.S., Dept. of Biology and Health Services
Karen S. Eisenhart, Ph.D., Dept. of Geosciences
Edinboro University of Pennsylvania, Edinboro, Pennsylvania, 16444
Introduction
Recently, land managers of the Uncompahgre Plateau have met collaboratively to develop a plan to restore degraded habitat while also meeting other pressing management objectives, such as mitigating wildfire risk in the wildland-urban interface. The product that they created is a spatially-explicit plan composed of treated, re-treated, and untreated areas called the “landscape mosaic” (Clements 2004). Implementation of the landscape mosaic began with new treatments in the Spring Creek / Dry Creek watersheds in 2003. One major goal of the plan, habitat restoration, relies on manipulating succession in order to enhance or eliminate particular characteristics of an ecosystem to the benefit of the species of concern, often game species. On the Uncompahgre Plateau, vegetation manipulations are carried out, in part, to enhance the winter range of mule deer. Habitat restoration implicitly relies on the recognition that vegetation structure influences the assemblage and behavior of animals through the distribution of cover and food resources, and in turn, the abundance and distribution of the animals impacts the survival, distribution and form of the vegetation comprising the habitat.
One important goal of treatments in this watershed, indicated above, is improvement of mule deer winter range. Populations of game species have been fairly well examined on the Uncompahgre Plateau over a number of years. However, little data exists regarding the nature of communities of small mammals in that area, particularly rodent species. Yet small mammals likely have a large impact on vegetation communities (Vander Wall 1990, Somers et al. 2003) and may ultimately play a role in the success of post-treatment seed applications. As granivores, rodents have the capacity to remove seeds through seed predation or to disperse seeds into seed larders or through scatter-hoarding seeds into seed caches of one or several seeds (Vander Wall 1990). They also may impact vegetation through herbivory of the reproductive organs of many plants.
Clearly the population abundance of rodent species has the potential to strongly impact the distribution and structure of many types of plants, including tree and shrub species, forbs, and grasses. Little is known about their role in structuring the vegetation on the Uncompahgre Plateau, or indeed in other communities throughout the semi-arid West. A few studies have measured population abundance and species richness in natural communities, including in woodlands during mast and non-mast years (Table 1). Other research in treated and untreated woodland and shrub communities suggests that the abundance of many rodent species increases following mechanical treatment, but may decline again within a number of years following treatment (Table 1, Baker and Frischknecht 1973, Severson 1986, Turkowski and Reynolds 1970). The impact of treatment appears to be species-dependent, and may be strongly correlated to the structure of vegetation and debris that results from treatment practices. Importantly for management, the period of increase in small mammal populations occurs in conjunction with natural and artificial post-treatment seeding, which may negatively impact the success of individual treatments.
We suspect that the small mammal populations of the Uncompahgre Plateau behave in a similar manner to communities studied elsewhere (Table 1), although the actual assemblage of species in Uncompahgre Plateau vegetation will not precisely duplicate those found in other regions of the West. We feel that it would be worthwhile to study the small mammal communities of the Uncompahgre Plateau. Many interesting questions regarding the dynamics of small mammal populations and their interaction with habitat could be addressed particularly well by the natural laboratory of vegetation treatments on the Uncompahgre Plateau.
Within a relatively small area the Spring Creek / Dry Creek watershed presents several adjacent vegetation treatments that are repeated across several mesas and which are separated by moderately deep draws. Since the home range of many rodents species are small, we anticipate that the system of old chaining with recent re-treatments embedded, patches of high mortality in untreated areas, and mature woodlands present an opportunity to study the impact of treatment on small mammal communities through time. By sampling small mammals and their habitats in this semi-natural research laboratory we also hope to explore the impact of the small mammal communities on the vegetation. Ultimately, rodents must impact the community of larger vertebrates (and vice versa) through impacts on the vegetation.
We propose to study small mammals on several of the mesa tops near Route 90, west of Montrose, where management objectives have been to restore ecosystems in a way that serves several objectives. To this end, we have already conducted a pilot study for two weeks during July 2005 (preliminary results below). We anticipate that the proposed study for 2006 will provide the following baseline information to the Colorado Division of Wildlife:
1) a record of the small mammal assemblage in the study area
2) degree of variation in small mammal communities among treatment types
3) degree of variation in small mammal communities among mesa systems
4) whether any species might serve as an indicator of habitat condition
5) ecological impacts of treatments on rodent communities, and vice versa