Theses and Dissertations at Montana State University (MSU)
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Item Long-term response of willow to beaver reintroduction and moose browsing in the southern Absaroka-Beartooth Wilderness(Montana State University - Bozeman, College of Agriculture, 2022) Dines, Rachael Helen; Chairperson, Graduate Committee: Bok SowellWillow is an important component in the southern Absaroka Beartooth Wilderness (ABW) riparian areas because it provides critical beaver habitat and is an essential food source for moose populations. Forest Service managers have monitored long-term trends in willow condition and herbivore populations in the southern ABW. Beavers were extirpated in the mid-1900's and then reintroduced beginning in 1986. Moose numbers increased in the early 1900's and willow over-browsing followed until the population declined after habitat loss from the 1988 Yellowstone fires. The objective of this study was to examine willow condition in response to changes in beaver and moose populations in the southern ABW. I used annual stream-side surveys to record the number and location of beaver colonies from 1986 to 2021 and aerial imagery to describe changes in willow canopy cover. I used a binomial regression to evaluate the relationship between willow canopy cover and beaver colony density and longevity to estimate if long-term beaver presence increased willow canopy cover. I used linear regression to analyze indices of moose relative abundance, willow plots recording height and browsing, and a long-term browsing exclosure to evaluate the effect of moose population trends on willow height. Beaver have remained at carrying capacity over the last 20 years, and average willow canopy cover increased from 16% in 1981 to 37% in 2019. The probability of willow occurrence increased the longer beaver occupied an area and with colony density (colonies/km). Moose relative abundance declined from 1987 to 2021, while average willow height increased from 113cm in 1988 to 190cm in 2021 and browsing decreased from 53% in 1989 to 3% in 2021. Browsing was an important factor limiting willow height. Moose abundance had a positive linear relationship with average browsing pressure and negative linear relationship with average willow height. This study shows that the southern ABW was able to recover from historic over-browsing and beaver extirpation. The long-term effects of beaver reintroduction and reduced moose numbers in a historically degraded environment enhanced willow, indicating that under the right circumstances, willow communities have the potential to recover from a previously degraded state.Item Temperature, light, and soil effects on the establishment of Bebb's willow (Salix bebbiana)(Montana State University - Bozeman, College of Agriculture, 1989) Atchley, Jennifer LauraItem Relations of moose, cattle, and willows in southwestern Montana(Montana State University - Bozeman, College of Letters & Science, 1969) Dorn, Robert D.Item Evaluation of tall willows (Salix spp.) within a livestock grazing allotment in southwest Montana(Montana State University - Bozeman, College of Agriculture, 1994) Manoukian, Mark EdwardItem Change in deciduous woody vegetation, implications of increased willow (Salix spp.) growth for bird species diversity, and willow species composition in and around Yellowstone National Park's Northern range(Montana State University - Bozeman, College of Letters & Science, 2009) Baril, Lisa Marie; Chairperson, Graduate Committee: Andrew J. HansenDeciduous woody vegetation (DWV) in Yellowstone's northern range is a rare, but important habitat type. Including willow, alder, aspen, and cottonwood, DWV was limited in height and areal extent since the early 1900s. Since the mid-1990s; however, DWV has increased in height and areal extent in some locations. Previous studies regarding DWV change have focused on quantifying change in vegetation growth in areas of limited extent and none have quantified increased DWV growth at the scale of the landscape. Furthermore, no studies have evaluated the implications for increased growth of DWV for wildlife in the region or how DWV species themselves may influence rates of growth. In this thesis I evaluate change in DWV within wetland and riparian areas using aerial photographs from 1991 and 2006. I also investigate how an increase in willow, the dominant component of DWV in the region, has likely influenced bird diversity. Finally, since willow species vary with respect to genetic limitations on growth and reproduction that in turn may influence observed patterns of growth; I examine willow species composition across the northern range. Results of the air photo interpretation revealed a 170% increase in DWV. Most plots that increased did so by recruitment rather than densification; however, DWV was difficult to detect below 100 cm indicating that the number of plots increasing by recruitment may have been overestimated. Bird community variables were examined in three willow growth conditions: height suppressed, recently released, and previously tall (tall prior to observed increase in growth). I found that willow structure generally increased in complexity from structurally simple height suppressed willows to structurally complex previously tall willows and that this allowed for greater bird richness, abundance, diversity, and the abundance of several willow dependent bird species. I also found that willow species composition was similar and diverse between the released and previously tall condition, but that the suppressed condition was dominated by a singe species. I conclude that increased DWV has allowed for greater bird diversity in the northern range and that increased willow growth in the suppressed condition may be influenced by species composition there.Item Trophic basis of invertebrate production in a Northern Rockies stream with recent willow recovery(Montana State University - Bozeman, College of Letters & Science, 2011) Junker, James Robert; Chairperson, Graduate Committee: Wyatt F. CrossEcologists have long recognized that ecosystems are not isolated in the landscape and can receive inputs of energy, materials, and organisms from beyond their boundaries. The role of these inputs for consumers in receiving ecosystems depends on biotic and abiotic characteristics of both the donor and recipient ecosystems. In streams, the influence of leaf litter input from terrestrial environments on stream structure and function has received much study. Recently, riparian vegetation in Yellowstone National Park has undergone increases in growth and distribution in many areas, however the implications for food webs of adjacent stream ecosystems has remained unexplored. In this study, we combined stable isotope ratios of food web components with estimates of invertebrate secondary production to measure the relative importance of terrestrial organic matter and algae to stream invertebrate production. We found stable isotope ratios of terrestrial litter were relatively constant throughout the annual cycle. In contrast, algae showed varying patterns of enrichment and depletion likely driven by changes in light, discharge, and sources of dissolved carbon and nitrogen. Mean annual secondary production was 7.5 g AFDM m -² y -¹ (95% CI; 7.0-8.2), and the majority of this production was supported by stream algae (58%; terrestrial detritus supported 42%). Invertebrate production varied seasonally, with >50% of annual production occurring between July and September. Relatively high quality algae supported the majority of production during this critical growth period characterized by warm temperatures and high NPP. Terrestrial litter supported the majority of invertebrate production (57%) during cold months between October and May, when stream NPP and metabolic demands of invertebrate consumers were low. Our findings demonstrate that high quality resources support invertebrate production during periods of high metabolic demand, while terrestrial litter provides an abundant resource to support invertebrate consumer production when higher quality resources are scarce and metabolism is reduced. This study provides a quantitative measure of the importance of allochthonous and autochthonous resources to an invertebrate community of a northern Rocky Mountain stream, and provides a benchmark to assess the potential impacts of changing riparian vegetation on streams within the northern Rocky Mountains.