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James ForesterAdvisor: Monica Turner PhD 2005: Animal movement and habitat use in heterogeneous landscapes: elk (Cervus elaphus) responses to forage, predation and disturbance in Yellowstone National Park, USA. Vegetation, predation and natural disturbance may interact in complex ways to influence habitat use by elk (Cervus elaphus), yet these interactions are poorly understood. I used field studies and statistical modeling of Global Positioning System (GPS) biotelemetry data to address how the movement patterns and habitat selection of female elk vary with landscape characteristics at multiple scales in Yellowstone National Park, USA. First, I used a state-space statistical approach to model the internal behavioral state and the proximate movement response of elk to available forage biomass, landscape composition, topography, and wolf (Canis lupus) density. Second I used logistic regression to examine habitat use among individual elk at broad (home range) and fine (700-m radius) scales. Finally, I used fecal pellet counts to examine if dense aggregations of coarse wood and pine saplings provide browsing refugia for aspen (Populus tremuloides) seedlings in areas burned by wildfires in 1988. The state-space analysis showed a consistent, strong pattern of
increased movement by elk during the crepuscular hours. While landscape
factors influenced both the behavioral state and the proximate movement
response, the specific variables included in the best-fitting models
varied substantially among individual elk and were not explained
by animal or home range characteristics. In the habitat-use analysis,
elk avoided areas of high wolf density and selected for areas that
provided a mixture of high-biomass grasslands and high-cover stands
of young coniferous forest. The importance of some covariates in
individual-based models could be explained by characteristics of
the animal (age) and its home range (amount and spatial configuration
of open area). The results of both the state-space and habitat-use
analyses indicate that a careful consideration of individual variability
may help produce more general models of habitat use. Variability
in pellet counts was not explained by the density of logs or pine
saplings. Aspen seedlings were heavily browsed throughout the study
area and were less likely to be found in areas with greater elk
use. These results suggest that fire-induced coarse wood piles and
pine sapling thickets may not create broad-scale browsing refugia
for aspen in the landscape of central Yellowstone National Park.
MS Abstract 2002: Landscape and local factors affecting northern white cedar recruitment in the Chequamegon National Forest, WI. Northern white cedar (Thuja occidentalis) stands throughout the
upper Midwestern United States have failed to consistently recruit
individuals to the canopy for several decades. We recorded the abundance
of cedar seedlings and saplings in 23 lowland cedar stands in the
Great Divide District of the Chequamegon National Forest, WI. We
discovered that seedlings (height <22 cm) were common throughout
the study area but recruitment of cedar was extremely low. Only
three large saplings (height >100 cm) were counted across all
transects, and small saplings (height = 22 to 100 cm) were also
rare. Furthermore, over 60% of the small saplings exhibited browse
damage. Density of seedlings was positively related to distance
to roads, cedar basal area, and the proportion of cedar and non-wetland
coniferous forest in a 1 km radius. The presence of small saplings
was negatively related to the proportion of mature deciduous forest
in a 1 km radius, dense canopy cover, and high edge-to-area ratios
of the cedar stand. We discuss the implications of timber harvesting
practices and ungulate population management on the long term persistence
of northern white cedar in the Chequamegon National Forest. |
