College of Forestry

Global Trophic Cascades Program

Graduate Studies

Master of Science - This concentration is designed for students interested in topics that intersect forestry and wildlife science as an interdisciplinary approach to attaining sustainability of both forest and wildlife resources. Additional coursework in forestry, statistics, spatial analysis, and/or the biological sciences may be suggested.

Doctorate in Philosophy- This concentration is designed for students interested in topics that intersect forestry and wildlife science as an interdisciplinary approach to attaining sustainability of both forest and wildlife resources as well as entire ecosystems. Additional coursework in forestry, statistics, spatial analysis, and/or the biological sciences may be suggested.

Current Graduate Students:

Christopher Wolf, PhD Student. Globally, a significant number of mammalian species are endangered.

My research involves using statistical and macroecological tools to better understand the drivers of species endangerment. I am particularly interested in the relationships between life history traits and extinction risk. This research could have policy implications for biodiversity conservation. I am also interested in the ecological effects of predators, especially wolves and other large carnivores, and the unique challenges associated with their conservation.

Previous Graduate Students:

Jonathan Batchelor (MS). Restoration of Riparian Areas Following the Removal of Cattle in the Northwestern Great Basin.

We assessed the effects of the elimination of livestock in riparian systems at Hart Mountain National Antelope Refuge in southeastern Oregon, 23 years after the removal of cattle grazing, using 64 photos taken before grazing was removed compared with later retake photos. Two methods were used for this assessment: (1) a qualitative visual method comparing seven cover types and processes and (2) a new quantitative method of inserting digital line transects into photos. Results indicated that channel widths and eroding banks decreased in 64 and 73 % of sites, respectively. We found a 90 % decrease in the amount of bare soil (P\0.001) and a 63 % decrease in exposed channel (P\0.001) as well as a significant increase in the cover of grasses/sedges/forbs (15 % increase, P = 0.037), rushes (389 % increase, P = 0.014), and willow (388 % increase, P\0.001). We also assessed the accuracy of the new method of inserting digital line transects into photo pairs. An overall accuracy of 91 % (kappa 83 %) suggests that digital line transects can be a useful tool for quantifying vegetation cover from photos.
Hart Mountain Website

Batchelor, Jonathan L., William J. Ripple, Todd M. Wilson, and Luke E. Painter. "Restoration of Riparian Areas Following the Removal of Cattle in the Northwestern Great Basin." Environmental Management, February 19, 2015, 1-13. doi:10.1007/s00267-014-0436-2.


Luke Painter (PhD) Trophic cascades in the Greater Yellowstone Ecosystem: ecological interactions of wolves, elk, bison and woody browse plants

Woody plants that are eaten by elk (Cervus elaphus) were suppressed by intensive browsing in Yellowstone National Park (YNP) and the surrounding area during the period of wolf (Canis lupus) absence in the 20th Century. Following the return of wolves to the Yellowstone area in 1995 and 1996, wolves flourished and elk population density declined on the northern winter ungulate range. Elk distribution and use of habitat also changed. As part of the trophic cascades program at OSU, I investigated the possibility that a trophic cascade from wolves to elk to plants has produced significant changes in rates of browsing by elk of aspen (Populus tremuloides), willow (Salix spp.), and cottonwood (Populus balsamifera and P. angustifolia), resulting in increased height of young plants and increased recruitment to heights above the reach of elk. I also hypothesized that increased bison (Bison bison) population density in northern YNP since the return of wolves has resulted in high browsing rates of these same plant species by bison. I carried out a three-part research plan to investigate these hypotheses.

Part 1. Effects of bison on willow and cottonwood in northern Yellowstone National Park
In the summer of 2010, I measured the effects of bison browsing on willow and cottonwood in the Lamar Valley area of Yellowstone National Park. I used the season and height of browsing to distinguish the effects of bison from those of elk, and showed that bison had a biologically significant effect on the growth of these plant species. This study also provided evidence for a trophic cascade from wolves to elk to browse plants, by showing that elk browsing has declined and plant growth increased where bison were not a confounding factor. I published a paper presenting this research, the first published research on the effects of bison browsing on woody plants in YNP

Part 2. Aspen, elk, wolves and trophic cascades in a multiple-use landscape
The second phase of my research was an analysis of change over time in aspen stands in the Greater Yellowstone Ecosystem, repeating measurements made by OSU PhD student Eric Larsen in 1997 and 1998. Larsen's work provided a baseline for aspen conditions shortly after wolf reintroduction. In the summer of 2011 I revisited aspen stands sampled by Larsen in the Sunlight Creek and Crandall Creek valleys in the Shoshone National Forest adjacent to YNP, and collected data on browsing intensity and height of young aspen. If browse rates have declined and aspen have increased in height, this would provide evidence of a trophic cascade from wolves to elk to aspen. If these changes occurred while elk density has remained stable, this would point to a behaviorally mediated trophic cascade, where aspen have benefited from changes in elk habitat use and foraging behavior, rather than changes overall elk density. Results show evidence of a trophic cascade, with increased height of young aspen related to lower rates of browsing. Cattle were an important factor increasing the rate of browsing on aspen. This research may be the first to show a trophic cascade from wolves on a multiple use landscape, outside of a national park. A paper written from this research is now in review.

Part 3. Aspen, elk, wolves and trophic cascades in the northern Yellowstone ecosystem 
In the summer of 2012 I will continue the study of aspen regeneration and trophic cascades, using the same methods as my 2011 study in the Shoshone National Forest. I will compare measurements between 1998 and 2012 in stands previously measured by Eric Larsen inside Yellowstone National Park. This study has distinct advantages over some previous studies of trophic cascades in the park, including a larger number of stands randomly selected across a wider area, the ability to compare across a span of time against a baseline measured shortly after wolf reintroduction, and the perspective provided by the continuing development of the wolf-elk-aspen relationship over time. Results from my 2011 work in the Shoshone National Forest showed an additional impact on aspen from browsing by livestock, and I will see if a similar effect is discernible in the park from bison. Research showing a trophic cascade from wolves to elk to aspen in YNP has been controversial. This new study will shed new light on the unfolding story of the ecological effects of wolves in the Rocky Mountains.

Painter, LE, and WJ Ripple. in review. Aspen, elk, wolves and trophic cascades in a multiple-use landscape.
Painter, LE, and WJ Ripple. 2012. Effects of bison on willow and cottonwood in northern Yellowstone National Park. Forest Ecology and Management 264: 150-158. 
Ripple, WJ, LE Painter, RL Beschta, and CC Gates. 2010. Wolves, elk, bison, and secondary trophic cascades in Yellowstone National Park. Open Ecology Journal 3: 31-37.

Josh Halofsky (PhD) Trophic cascades and aspen recruitment in the Gallatin range of Southwest Montana
The study examined the relationship between wolf, elk, and aspen within the framework of trophic cascades inside and outside of the Gallatin elk winter range. The overall goal of this study was to determine if an association exists between current aspen recruitment and historic and current elk browsing activities as affected by the absence or presence of wolf predation. This study also examined if environmental factors (climate, conifer invasion) may have had a role in aspen recruitment. Through the examination of current and historic elk browsing levels, current and historic browsing effects on aspen recruitment can be addressed. Historic browsing levels will be determined through tree ring analyses and aspen age structures. Current browsing levels will be assessed based on elk pellet counts and plant architecture methods. Current browsing will be assessed based on predation risk and viewshed using a digital elevation model.

Jeff Hollenbeck (PhD) Multi-scale bird-aspen habitat relationships in the Northern Yellowstone Ecosystem
I conducted an investigation of the relationships between birds and aspen habitat in the northern Yellowstone Ecosystem with an emphasis on migratory bird species. The highly researched aspen of the northern ungulate range provide a rich context in which to understand how birds use and distribute themselves among aspen patches at multiple scales (patch, landscape, and regional). Specific questions include: (1) Do avian species diversity vary as a function of conifer presence in aspen habitat? (2) Do aspen patches intercept migratory birds during northward migration? and (3) How do birds respond to differences in aspen patch structure resulting from differing land management approaches in the northern Yellowstone Ecosystem?

Andrea Laliberte (PhD, June 2003) Human Influences on Historical and Current Wildlife Distributions from Lewis & Clark to Today
Although it is well known that humans are strong modifiers of their environment, there is a need for greater understanding of human-wildlife interactions, both historically as well as currently. Historical journals can help shed light on early human-wildlife interactions, and the Lewis & Clark journals contain some of the earliest and detailed written descriptions of a large part of the United States before Euro-American settlement. I used the journal entries to assess the influence of humans on wildlife distribution and abundance. Areas with denser human population, the Columbia Basin and the Pacific Coast, had lower species diversity and abundance of large mammals. The opposite was observed on the Plains. Overhunting before Euro-American contact accentuated by the introduction of the horse may have been major contributors responsible for the historic absence of some species that are present in the archaeological record. The information gained from the Lewis & Clark journals shows the considerable human influence on wildlife under relatively low human population densities. This has major implications for conservation biology and ecological restoration, since human influence is often underestimated when considering the pre-settlement condition.

Species ranges are dynamic and change greatly over time. In order to identify large-scale patterns in range contractions and/or expansions, I compared historic and current geographical ranges of 43 North American carnivores and ungulates. Seventeen of the species had undergone range contractions over >20% of their historic range. In areas of higher human influence, species were more likely to contract and less likely to persist. Species richness declined considerably since historic times, and the temperate grasslands and temperate broadleaf/mixed forest biomes lost the highest average number of species, while the boreal forest and tundra showed fewer numbers of species lost. The study of species range changes contributed new quantitative information about human influences on range contractions in North America. The results can be used to improve our knowledge of historical reference conditions, for the creation of wildlife reserves, and for wildlife re-introductions.

Eric J. Larsen (PhD, July 2001) Aspen Age Structure and Stand Conditions on Elk Winter Range in the Northern Yellowstone Ecosystem
Aerial photographs and field sampling were used to compare aspen (Populus tremuloides) age structure and stand conditions on elk winter range in the northern Yellowstone ecosystem. The elk winter ranges studied were the northern range in Yellowstone National Park (YNP) and the Gallatin National Forest, and the Sunlight/Crandall elk winter range in the Shoshone National Forest. I found significant differences when comparing aspen stands inside and outside of YNP borders. The aspen stands in the Gallatin and Sunlight/Crandall areas had a greater incidence of tall aspen suckers and stems in the 1-4, 5-9, and 10-19 cm diameter at breast height (DBH) classes. Aspen stems within YNP had a significantly higher percentage of stems with high levels of bark damage (>66% of bark surface damaged on the lowest 3 m of stem) than aspen stems in the Gallatin or Sunlight/Crandall.

An aspen age structure was developed using 598 increment cores. The aspen age structure in YNP was significantly different than the age structures of the Gallatin and Sunlight/Crandall elk winter ranges. The Gallatin and Sunlight/Crandall areas did not have significant differences in their age structures. The greatest differences between YNP and the National Forest areas was in the younger age classes, measured as aspen stems originating between 1920-1989.

Aspen stands have successfully recruited new stems into their overstories in all habitat types from 1880-1989 on the Sunlight/Crandall elk winter range and the Gallatin’s portion of the northern range. Within YNP, aspen stands successfully recruited new overstory stems between 1860-1929 in all habitat types. Since 1930, YNP aspen have successfully recruited overstory stems only in scree habitat type stands and other areas protected from browsing. I discussed several potential ecological factors impacting aspen overstory recruitment and conclude that changes in ungulate browsing patterns best explains the spatial and temporal patterns observed

Tad Larsen (MS, July 2004) Modeling Gray Wolf Habitat in Oregon Using a Geographic Information System
Gray Wolves (Canis lupus) were once found throughout North America including Oregon. Wolves were extirpated from Oregon due to heavy hunting pressure in the late 19th and early 20th centuries and have been absent for over 50 years. Successful reintroduction efforts in Idaho and the greater Yellowstone area have caused wolf populations in the Rocky Mountain region to rise dramatically, giving way to wolf dispersal into Oregon. This research used logistic regression and a Geographic Information System (GIS) to model and assess potential wolf habitat in Oregon. Models based on previous research were analyzed to find the best approximating wolf habitat model. These a priori models were formulated under the hypotheses that wolf habitat (1) will include relatively high densities of prey, (2) will be limited by human influence, (3) will include favorable landscape characteristics (e.g. forest cover, public ownership), and (4) may be influenced by some combination of these factors. The final model was tested and validated with wolf pack data from the Rocky Mountain region. The results show that a habitat model including variables of forest cover and public land can successfully predict wolf habitat in the study area. These results may assist natural resource managers in developing and implementing of a wolf management plan in Oregon.

Amie Shovlain (MS) Oregon Spotted Frog Habitat Use and the Effects of Grazing
Limited information on grazing impacts on amphibians in the US northwest is available. I am studying the effects of livestock grazing on amphibian behaviour by assessing Oregon spotted frog (Rana pretiosa) microhabitat preference in grazed and ungrazed treatments on Jack Creek, Fremont-Winema National Forest, Oregon. The Oregon spotted frog was an ideal species to address this issue due to its rarity and potential vulnerability to disturbance. Secondary objectives of this study are to identify frog overwintering sites and migration routes, to provide a more complete understanding seasonal habit use.