Theses and Dissertations at Montana State University (MSU)
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Item Climate-fire-vegetation dynamics in the Greater Yellowstone Ecosystem: recent trends and future projections in a changing climate(Montana State University - Bozeman, College of Letters & Science, 2020) Emmett, Kristen Dawn; Co-chairs, Graduate Committee: Benjamin Poulter and David Roberts; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Disdentangling climate and disturbance effects on regional vegetation greening trends' in the journal 'Ecosystems' which is contained within this dissertation.; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Adapting a dynamic vegetation model for regional biomass, plant biogeography, and fire modeling in the western U.S.: evaluating LPJ-GUESSLMFIRECF' submitted to the journal 'Ecological modelling' which is contained within this dissertation.; Benjamin Poulter was a co-author of the article, 'Processed-based modeling approaches for climate-vegetation-fire feedbacks in the Greater Yellowstone Ecosystem' which is contained within this dissertation.Climate change threatens to change forested ecosystems and wildfire characteristics across the globe. For the Greater Yellowstone Ecosystem (GYE), under future warming temperatures, wildfire activity is expected to increase and the suitable habitat for many dominant tree species is expected to shrink. Previous studies predict large high severity fires to occur more frequently, potentially so frequent that forests are unable to grow old enough to produce seeds and self-regenerate. Studies of suitable climate spaces show that previously habitable areas may become too warm or dry to support common GYE trees. The first goal of this dissertation was to use vegetation images from satellites to detect recent changes in forest productivity in the GYE, and then determine the relative importance of recent climate and disturbance observations in explaining these changes. We found that areas with detected increases in plant growth, or 'greening' trends, were associated with forested areas regenerating after wildfire. Detected decreases in plant growth, or 'browning' trends, were associated with areas that had recently burned. Historically dry areas with recent increases in precipitation were associated with greening trends. Warming of 0-2 °C was associated with greening trends, while greater increases in temperature (>2 °C) were correlated with browning trends. The key take-away is although forests in the GYE are usually considered temperature limited, changes in precipitation may be more important than previously thought. The second goal of this dissertation was to adapt a global vegetation computer model for regional applications to simulate forests and wildfire dynamics, ultimately to run simulations under future climate conditions to predict how forest extent and composition may change. Life history characteristics and climate limitations were aquired for the dominant GYE plant types to dictate their establishment, growth, competition, and mortality in the new model. Before running future simulations, it is required to evaluate how well the model represents current conditions. Adding new equations that calculate the initiation, spread, and effects of crown fires was required to reproduce recent vegetation abundance, distribution of plant types, and fire activity in the GYE. Methods, expected results, and implications of running future simulations are described in Chapter 4.Item Understanding the effects of wildfire on the functional traits of plants and bees(Montana State University - Bozeman, College of Letters & Science, 2018) Durney, Janice Simone; Chairperson, Graduate Committee: Laura BurkleDiversity, often assessed by species richness, fosters ecosystem success, promoting ecosystem services, stability, and adaptation. Evaluations of functional trait composition are a better indicator of ecological process dynamics. Functional trait variation of species within a community (i.e., inter-specific variation) and of individuals within a species (i.e., intra-specific variation) may reflect adaptations and phenotypic variation contributing to the functional diversity of a community in the face of change. Wildfires have shifted from mixed-severity to frequent high-severity fires, due to fire suppression and climate change, modifying ecosystem function, trait selection pressure, and species sorting. Traits involved in plant-pollinator interactions can be used to understand the mechanisms underlying shifting interactions across communities and how post-wildfire environmental conditions affect community assembly, structure, and stability. We tested how productivity, time-since-burn, and wildfire severity influenced mean functional trait values and inter- and intra-specific functional trait variation of plants and bees known to interact in southwestern Montana, USA. Fieldwork was conducted from 2013-2017 in two locations that differed in productivity with similar fire histories of recent-mixed-severity, recent-high-severity, older-high-severity burns, and unburned areas. Functional traits involved in plant-bee interactions were selected and measured among plant and bee species observed across these various productivity, time-since-burn, and fire severity levels. We found that as productivity and time-since-burn increased, the mean functional trait values and inter- and intra-specific functional trait variation of plants and bees increased. In addition, productivity, time-since-burn, and fire severity affected the functional trait values and variation of plant species more than bee species. These results suggest that as productivity and time-since-burn increases so does trait diversity - promoting ecosystem function and stability. The increased effect of productivity and time-since-burn on plant functional traits compared to bee traits suggests the dispersal abilities of bees allow them to cope with the effects of fire, while plant species are more prone to productivity and time-since-burn habitat filtering and species sorting, potentially due to limited mobility. Our results support previous findings that shifting wildfire regimes from mixed to high-severity burns increases species sorting and limits trait variation after wildfire regardless of productivity but trait variation increases as time-since-burn and productivity increases.Item Plant-pollinator network assembly after wildfire(Montana State University - Bozeman, College of Letters & Science, 2018) Simanonok, Michael Peter; Chairperson, Graduate Committee: Laura BurklePlant-pollinator networks are threatened by anthropogenic influence due to habitat loss, changing fire regimes, climate change and other factors. Furthermore, we have little current knowledge for how species interactions and processes like pollination assemble and recover post-disturbance. Studying the mechanisms by which plant-pollinator interactions assemble in a post-disturbance landscape, particularly across gradients of disturbance intensity and successional time, would greatly help in building foundational ecological knowledge regarding the assembly of species interactions as well as provide specific information to aid conservation and management. Therefore, we investigated plant-pollinator network assembly after wildfire, between mixed- and high-severity burns and across time-since-burn, and we asked i) how do network structure and the network roles of persistent species vary ii) how does wildfire change the nutritional landscape of available floral pollen quality and how does that influence bumble bee foraging and nutrition, and iii) how do nesting and floral resources affected by wildfire influence wood-cavity-bee nesting success and richness? Our study design involved four wildfires from the Absaroka Mountains of southwest Montana, USA, which included a range of burn severities as well as a 1-25 year chronosequence of time-since-burn sampled primarily from 2014 to 2016. Bees were sampled via hand netting and nesting boxes alongside floral census transects and pollen sampling to assess metrics important to plant-pollinator network assembly, available floral pollen quality, bumble bee nutrition, and wood-cavity-nesting bee nesting success. The primary findings are that i) plant-pollinator network structure does not dramatically shift with burn severity or time-since-burn, nor do the network roles of persistent species, ii) available floral pollen quality and bumblebee nutrition are limited by high-severity burns, and iii) burn severity has little effect on the nesting success of wood-cavity-nesting bees. The conclusions that follow these results are mainly that i) evidence of constant structure and low variance of species' roles provides evidence for preferential attachment over opportunistic attachment in assembling plant-pollinator networks post-disturbance, ii) varied species composition between mixed- and high-severity burns may mean that bumble bees are nutritionally limited in high-severity burns, and iii) nesting resources do not appear to strongly limit nesting success or richness of wood-cavity-nesting bees.Item The influence of post-wildfire logging on forb and pollinator communities and forb reproductive sucess, Gallatin National Forest, Montana(Montana State University - Bozeman, College of Letters & Science, 2016) Heil, Laura Jean; Chairperson, Graduate Committee: Laura BurklePollinators are in decline worldwide, and these declines have implications for flowering plants and their reproduction, given that 80% of flowering plants depend on insects for pollination. One potential contributor to pollinator species' declines is shifts in disturbance regimes, such as increased severity and frequency. Wildfires are essential natural disturbances that are important drivers of forest biodiversity in the western U.S., and there is often pressure to respond to wildfire with management including post-wildfire logging. This management strategy involves the removal of dead trees for economic value immediately following wildfire. Thus, is expected that post-wildfire logging has additional impacts on forest communities compared to non-salvage logging, and that it impacts forb and pollinator communities. Several studies have examined the short-term responses of forb and pollinator communities to wildfire and non-salvage logging individually, and one study examined their combined effects. However, no studies have examined the long-term effects of post-wildfire logging, on forb and pollinator communities and on forb reproduction. My research addresses these gaps in knowledge and asks: 1) how do floral and bee communities respond to post-wildfire logging and how do their responses differ between two different-aged fires, and 2) how does post-wildfire logging influence forb reproduction and pollen limitation of reproduction in an older wildfire? In the more recent fire, floral and bee density and species richness were higher in logged than unlogged areas. By contrast, in the older fire, forb and bee communities were similar between logged and unlogged areas. Unexpectedly, we found large inter- and intra-annual variation in the effects of post-wildfire logging. Lastly, in the older fire, there were no effects of post-wildfire logging on forb reproduction, but plants were pollen limited in unlogged areas. This suggests that plants in unlogged areas are able to augment their reproductive output with supplemental pollen resources, but plants in logged areas cannot. Together, these results suggest that post-wildfire logging is beneficial for forbs and pollinators in the short-term, and these positive effects depend on time of growing season and sampling year. However, post-wildfire logging may be detrimental for forb reproduction in the long-term.Item Changes in native and nonnative fish assemblages and habitat following wildfire in the Bitterroot River basin, Montana(Montana State University - Bozeman, College of Letters & Science, 2005) Sestrich, Clint Michael; Chairperson, Graduate Committee: Thomas E. McMahonWildfire frequency and severity have increased over the past decade but few studies have assessed the effects of large, intense fires on native salmonids in the Intermountain West. I utilized a unique data set with 1-11 years of pre-fire population data in 24 small streams in the Bitterroot River basin in western Montana to determine if habitat changes caused by a large (1,108 km 2) wildfire and associated debris flows favored nonnative brook trout Salvelinus fontinalis over native westslope cutthroat trout Oncorhynchus clarkii lewisii and bull trout S. confluentus. I used before-after control-impact (BACI) and extensive post-treatment study designs to determine whether changes in species abundance and habitat increased with increasing burn severity and debris flows. Species abundance was estimated pre- and post-fire with mark-recapture electrofishing and habitat conditions post-fire were assessed by measuring substrate, temperature, large woody debris, and habitat type. Stream temperature and sedimentation generally increased with burn severity whereas habitat complexity decreased with increasing burn severity and presence of debris flows. However, recovery of native trout populations was rapid with populations approaching or surpassing predisturbance levels within three years. In contrast, brook trout recovery was less apparent especially in debris flow reaches as the proportion of brook trout to the total salmonid assemblage decreased each year post-fire. However, one notable exception occurred in a high burn severity reach on Rye Creek, where brook trout increased by 499% and apparently replaced bull trout. Model results indicated that brook trout abundance was negatively related to stream gradient, elevation, and the proportion of a basin that was burned and positively related to watershed area, water temperature, and pool frequency. Spread of nonnative species to reaches where undetected pre-fire (n = 7) occurred irrespective of wildfire disturbance with brown trout Salmo trutta being the primary invading species (n = 5) and only one occurrence of brook trout and rainbow trout Oncorhynchus mykiss invasion. Although changes in aquatic habitat following wildfire have the potential to favor nonnative fishes, connected cutthroat trout and bull trout populations in the Bitterroot River basin were resilient to disturbance and generally recovered more rapidly than nonnative brook trout.