<p> Increasingly large and severe fires across the western United States are creating difficult challenges for land managers. Despite the wide usage of current post-fire hillslope treatments, their effectiveness varies. Some research even shows negative impacts, such as the spread of invasive species. </p><p> The use of select post-fire colonizing mosses or &ldquo;fire moss&rdquo; is a promising post-fire stabilization treatment and longer-term restoration tool that has never been investigated for use in high severity burned environments. Fire mosses possess traits that make them ideal candidates for restoration purposes such as: universal distribution, desiccation tolerance, high water holding capacity, and soil aggregation ability. Fire mosses also are apparently succeeded by vascular plants. Harnessing the restoration power of fire mosses, finding ways to bring them to additional critical post-fire sites, and hastening their arrival on scene could provide a valuable service not currently being utilized. Our research addresses the basic questions surrounding the effectiveness of fire mosses in post-fire stabilization and restoration since there is no know prior work in this field. Field experiments were conducted to determine if fire moss could be grown on post-fire sites. Results show that inoculation increased moss growth by nine times and moss cover was an order of magnitude greater on high severity burned plots than either moderate or unburned plots. Subsequently, greenhouse experiments were conducted to find optimal growth conditions under which an inoculum supply source could be grown for field application. Results show that greatest moss growth occurred under five and seven day per week watering schedules, with fire moss Bryum argenteum constituting a majority of overall moss growth in the less frequent watering schedules suggesting that this moss would be the best candidate for use in marginal fire moss habitat (lower elevation, drier, and more exposed sites). Additionally, mosses Funaria hygrometrica and Ceratodon purpureus grew more prolifically in sample units with ash, while the opposite was true for Bryum argenteum, suggesting that future research should be conducted on the underlying mechanism. Overall, fire moss showed promise as a plausible restoration material, leading us toward future research given its potential to avoid problems caused by other hillslope treatments.</p>

<p> Climate warming is increasing fire severity in boreal forests and can alter forest structure and carbon (C) dynamics in Cajander larch (<i> Larix cajanderi</i>) forests of Siberia, which occur over C and ice-rich yedoma permafrost. Altered forest structure may impact understory vegetation through changing canopy cover, permafrost thaw depth, and soil temperatures. The primary objective of this study was to assess the long-term impacts of fire-driven changes in tree density on understory composition, diversity, and C pools and the underlying soil organic layer (SOL). Shrubs dominated low density stands, likely from reduced canopy cover and thaw depth, while mosses dominated high density stands. Consequently, understory C pools decreased from 415.46 to 158.87 g C m^&ndash;2. Total SOL C pools remained unchanged as tree density increased. These findings suggest that fire-driven changes in tree density may alter understory composition and C pools, which could impact nutrient/water cycling and permafrost stability. </p><p>

Forest gaps play a major role in forest dynamics because increased resource availability favors plant species that differ from those in undisturbed forest. This dissertation investigates the spatial heterogeneity of resource availability in gaps, how it varies by site, and how it affects regeneration. Gap effects on resource availability and seedling growth were studied at three sites, which differed in drainage, using large gaps (108 m × 30 m) where light ranged from understory shade to full sun. Light levels in plots were measured using hemispherical photos; soil moisture, with a capacitance probe; soil temperature, with a portable thermocouple; and nitrogen, with buried-bag incubations. The strong asymmetric, light-induced temperature gradient drove nitrogen mineralization rates. Patterns of mineralization were modified by variation in soil moisture within sites and increased with the average moisture levels among sites. Nitrogen availability was highest in the center of gaps, while root uptake reduced nitrogen availability at the north edge. Contrary to predictions, relative height growth of Betula lenta growing in the north center of gaps was greater than that of B. papyrifera. For both species, the difference between understory and gap growth increased from least to most fertile sites. To separate the effects of resources on plant- and leaf-level responses in the two species, a greenhouse experiment was conducted with high and low levels of light, nitrogen, and water. High nitrogen increased height growth even in shade. Nitrogen also increased leaf area through greater leaf initiation and retention. High rates of growth in gaps is caused by nitrogen effects on leaf display and light effects on realized carbon gain. This research shows that increased nitrogen availability only occurs if gaps are large enough to increase soil temperatures that drive mineralization and to overcome the effects of root uptake near gap edges. It also highlights how the effects of canopy openings varies by site and how this can influence the regeneration of gap-dependent species.

Habitat loss and fragmentation are among the most serious threats facing amphibian populations globally. Given the prevalence of these threats, it is essential that conservation planners understand the spatial scales at which amphibian populations operate and minimize local and regional extinction risks. We conducted a landscape-level investigation of population processes in marbled salamanders (Ambystoma opacum) distributed among 14 seasonal ponds in western Massachusetts. Using capture-recapture methods, we monitored breeding populations from 1998 to 2005 to evaluate terrestrial movement distances (Chapter 1), develop methodology for identifying individuals (Chapter 2), quantify dispersal probabilities and distances (Chapter 3), and evaluate survival and breeding probabilities in adults and the degree to which they are correlated among breeding populations (Chapter 4). In six field seasons, we recorded over 6,000 captures of adult marbled salamanders and 8,000 captures of newly emerging juveniles. Six of the 14 ponds supported relatively persistent breeding populations. Nearly 100% of adults and over 70% of juveniles moved to terrestrial habitats farther than 30 m from breeding ponds, and some juveniles moved greater than 1,200 m in their year of emergence. Both first-time and experienced breeders showed high fidelity to natal ponds; however, 9% and 3.6% of these individuals, respectively, dispersed to non-natal breeding sites. Adult survival probabilities did not vary substantially between sexes or among most breeding populations. Simulations estimated that approximately 50% of individuals that survive to breed once do not live to breed again, but approximately 25% will survive to breed 3 or more times. Collectively, our results demonstrate that breeding populations of marbled salamanders are prone to significant variability over time, with much of this variability concentrated in the egg and larval life stages. Given relatively limited life spans and frequent reproductive failures, many breeding populations may be vulnerable to local extinctions over the course of several decades; however, occasional dispersal among populations may offset both genetic and demographic factors contributing to local extinction risks. Marbled salamanders in Massachusetts may be best described by a dynamic “source-sink” metapopulation model, suggesting that conservation strategies must extend beyond breeding wetlands to maintain adult survival and metapopulation processes.

Modern silviculture is shifting from even-aged management toward sustainable management of the diversity of forest communities. Traditional growth-and-yield models are too simple for this new approach, but mechanistic models that can incorporate the complexity are too general. This shift in emphasis presents important scientific challenges and creates a critical need to update our modeling approaches. One response has been to manage forests by mimicking natural disturbance. Windstorm is the dominant natural disturbance in forests of northeastern North America. In Chapter 1, I use a mechanistic model (SORTIE) to explore the sensitivity of forest composition and structure to the resistance of individual trees to wind disturbance and the roles of local dispersal and seedling establishment. The results show that species-specific resistance to wind: drives the community response to disturbance; interacts with local dispersal patterns to influence succession; and interacts with seedbed substrate dynamics to influence canopy population dynamics. Biotic disturbances are also an important natural disturbance in these forests. In Chapter 2, I quantify how the presence of beech bark disease (BBD) alters the resistance of beech to uprooting and stem break, and explore the sensitivity of forests to subsequent increases in coarse woody debris (CWD). Results show that small seeded species increased in basal area primarily due to the increase in CWD caused by BBD. The results highlight the important indirect effects that pathogens can have on forest community dynamics. Managing complexity also requires improving our understanding of competition among trees and species responses along environmental gradients. In Chapter 3, I use USFS FIA data to analyze the effects of competition on tree growth along gradients for eight tree species in New England. I use information theory to determine the relative weight of evidence for each model. No species showed strong evidence in support of one model over others, implying that the robustness of predictions based on the selected best model is questionable. The complexity of competitive interactions and growth along gradients and the importance of including secondary effects via model averaging highlight key challenges for the management of mixed-species, uneven-aged stands.

The conservation of large carnivores is dependent on comprehensive research programs within and surrounding protected areas. In many locations, protected areas are not large enough to support viable large carnivore populations, and thus it is essential to understand the ecology of predators outside of protected areas. On the commercial farms of northcentral Namibia, farmers have systematically removed the largest predators in order to protect their livestock. Leopards are the largest remaining carnivore, aided by their adaptable and secretive nature. In order to properly manage regional leopards, there were several questions about their population size, feeding ecology and movements that needed to be addressed. Leopard population estimates were generated through camera-trapping surveys within and surrounding the Waterberg Plateau Park. These surveys suggest that leopard population density is significantly higher outside of the park, most likely due to environmental factors within the park that limit potential prey. Leopards were shown to primarily feed on wild ungulates, preferring kudu over livestock which they appear to avoid even when livestock densities are higher than individual wild ungulate species. Leopard home ranges and movements were investigated on commercial farmlands where they were not shown to move between the farms and the park. Home range estimates were similar to previous studies for similar environments with marginal resources. Beyond the ecological studies, the attitudes and perceptions of farmers were incorporated into the study in order to assess local predator management with particular emphasis on leopards. Farmers used a variety of livestock husbandry techniques, with varying success. Although there were no clear techniques to reduce conflict, farmers were able to substantially reduce losses by using at least one technique to protect their stock against predators. Farmers listed depredation as the source of highest livestock loss, and leopards the species which caused the most conflict by occurrence. Farmers removed approximately 11 leopards per year in the region which is equal to a 14% off-take for the local population. Farmer tolerance was assessed by the % calf loss that farmers were willing to lose to predators annually. Tolerance rates were then compared to annual livestock loss. Leopards, being a charismatic animal for tourists and trophy hunters, were evaluated for potential financial benefits for farmers to mitigate losses. Region-wide management strategies are discussed.

In the dry subtropical forest of Tucuman Province, Argentina, I assessed effects of habitat fragmentation on (1) the insect pollinator fauna by monitoring visits to flowers of two dominant leguminous trees and by sampling bees with yellow pan traps, and on (2) pollination and seed production levels by determining stigmatic pollen load sizes, number of pollen tubes at the base of the style, and number of fruits per flower (fruit set) and seeds per fruit (seed set) in 16 plant species representing a variety of growth forms, and pollination and breeding systems. The experimental design involved five study sites each with continuous forest, a large ($>$2 ha) forest fragment, and a small ($<$1 ha) fragment. Comparisons in pollinator abundance and diversity between fragments and continuous forest were replicated across 4 sites. Comparisons in pollination levels and fruit and seed set were replicated across 1-4 sites depending on the plant species. The exotic honeybee (Apis mellifera) dominated the flower-visiting fauna associated with the two leguminous species. Frequency and taxon richness of native flower-visitors to both plant species declined with decreasing fragment size, but frequency of honeybee visits increased, so neither species experienced significant effects of fragmentation on total visitor frequency. Similarly, in pan trap samples the relative frequency of honeybees increased with decreasing fragment size, whereas native bees increased in number and species diversity with increasing size of forest patch and as spring progressed. Fragmentation-related declines in pollination and seed output (fruit set x seed set) prevailed in the subset of the Chaco flora I studied. Among species, fragmented plant populations recorded an $\sim$20% median decrease in pollination and seed output levels. However, mechanisms behind these declines differed across species. In three self-incompatible species, decreases in the number of pollen tubes with fragmentation could be related to declines in pollination quality rather than in the number of pollen grains deposited on the stigmas. Correlative evidence showed that fragmentation-related declines in pollination could limit seed output in some plant species, but an increase in seed abortion due to inbreeding depression could also affect fragmented plant populations. Comparisons among self-compatible and self-incompatible species did not show any differential effect of fragmentation with breeding system. Overall, the results of this study show that fragmentation may exert chronic, negative effects on pollinators, pollination, and seed output with potential effects on plant regeneration, forest dynamics, and total species diversity. These results also indicate that fragmentation may alter community and population processes through subtle and complex mechanisms.

<p> The introduction of lake trout <i>Salvelinus namaycush</i> into Yellowstone Lake preceded the collapse of the native Yellowstone cutthroat trout <i>Oncorhynchus clarkii bouvieri</i> population. As a system with a simple fish assemblage and several long-term data sets, Yellowstone Lake provided a unique opportunity to evaluate the ecology of a native salmonid in the presence of a non-native salmonid population undergoing suppression in a large natural lake. Diet data for Yellowstone cutthroat trout and lake trout were evaluated at varying densities to determine the effects of density on diet composition. Temporal diet shifts from 1996-1999 to 2011-2013 were likely caused by limitation of prey fish for lake trout. Diets, stable isotopes, and depth-related patterns in CPUE indicated lake trout > 300 mm consumed primarily amphipods, making them trophically similar to Yellowstone cutthroat trout from during 2011-2013. A lake trout removal program was initiated during 1995 to reduce predation on Yellowstone cutthroat trout. Abundance and fishing mortality were estimated for lake trout from 1998 through 2013 and Yellowstone cutthroat trout from 1986 through 2013. Density-dependence was evaluated by examining individual growth, weight, maturity, and pre-recruit survival as a function of abundance. In addition, a simulation model was developed for the lake trout-Yellowstone cutthroat trout system to determine the probability of Yellowstone cutthroat trout abundance persisting at performance metrics given potential reductions in lake trout abundance. Estimates of Yellowstone cutthroat trout abundance varied 5-fold and lake trout abundance varied 6-fold. Yellowstone cutthroat trout weight and pre-recruit survival decreased with increasing Yellowstone cutthroat trout abundance; however, individual growth and maturity were not related to abundance. Lake trout population metrics did not vary with lake trout abundance. Simulation model results were variable because of uncertainty in lake trout pre-recruit survival. Conservative estimates for required lake trout reductions were > 97% of 2013 abundance for a > 70% probability of Yellowstone cutthroat trout persistence at the performance metrics outlined in the Native Fish Conservation Plan. Lake trout removal will likely reduce lake trout abundance and result in Yellowstone cutthroat trout recovery if the amount of fishing effort exerted in 2013 is maintained for at least 15 years.</p>

<p> Though land conversion and flow alteration have heavily impacted the Sacramento River riparian ecosystem, restoration opportunities still exist in the hydrogeomorphically active Middle Reach. This study of riparian forest succession focused on six dominant riparian tree species to explore relative establishment timing and the potential impacts of altered flow regimes. We utilized tree inventory data and increment cores collected from riparian forest stands to establish a temporal chronosequence of floodplain surfaces and associated tree ages and colonization timing. Tree age calculations incorporated raw ring counts and sampling error simulations. Results were then used to construct species-specific, diameterage models and predict age distributions for all inventoried trees. Cottonwood&rsquo;s colonization window was longer than expected (up to 95 years after floodplain creation), whereas box elder and walnuts established on floodplains &lt;50 years old. This study lays the groundwork for future research into the health and development of the Middle Reach riparian forest.</p>

<p> The Luquillo Forest Dynamics Plot (LFDP) has played a critical role in the initial discovery and subsequent investigation of many processes that govern tropical island wet forest dynamics. Previous work has identified past land use as the main factor in creating forest community compositional and structural differences across the plot. The responses of different species to past land-use intensity and to hurricane disturbances have created an evolving forest mosaic ideal for studying tropical forest successional dynamics. I revisited the interaction of land-use legacies and natural disturbance in the LFDP with new data and new approaches, with the motivation to reveal new information about the relative roles of anthropogenic disturbance and environmental-niche partitioning on tropical plant communities over time. </p><p> In the context of tropical forests and their successional dynamics, I asked how succession resulting from a history of human land use and more recent hurricanes interacts with background environmental variation to effect community structure and diversity. Community dynamics, in terms of forest structure and composition, were summarized over a twenty-one year period, noticing a decreasing trend in species richness over time and structural maturation of the forest, shown by a decline in small stems (trees &lt; 10 cm diameter) as it recovered from the compound effect of two major hurricane disturbances &ndash; Hugo, 1989 and Georges, 1998. We evaluate the magnitude of past human land use effects over time and define indicator species for areas of differing land-use pressure within the 16-Ha permanent LFDP. Using redundancy analysis, plant community-environmental relationships with respect to soils and topography are quantified. Spatial variables, computed using a principle coordinates of neighborhood matrix, explained the majority of the variability in plant community composition between areas of high and low past land-use within the LFDP, meaning environmental differences (e.g. niche differentiation among tree species) were found to be secondary to land-use legacies in determining forest community composition. </p><p> Over two decades, the effect of past land-use peaked about 15-years following the first of two hurricanes, and remained relative stable over time. Despite damaging the forest, hurricanes preserved community differences in species composition and reinforced structural asymmetries due primarily to two species; <i> Dacryodes excels</i> Vahl., a dominant primary forest tree species, and <i> Casearia arborea</i> (Rich.) Urb., an abundant secondary forest species. Abiotic environmental factors (e.g. soil resources and topographic variation) were weak at explaining differences in forest community composition. Plant community-environmental relationships were stronger in more anthropogenically-disturbed areas, suggesting long-term effects of land use on tropical forest communities on current community dynamics.</p>