Amphibians are in decline globally and a significantly greater percentage of ambystomatid salamander species are in decline relative to other species; habitat loss contributes significantly to this decline. The goals of this thesis is to better understand extinction risk in a marbled salamander (ambystoma opacum) population and how forestry effects extinction risk. To achieve this goal we first estimated an important life history parameter (Chapter 1) then used a metapopulation model to estimate population viability and determine what aspects of their life history put them most at risk (Chapter 2) and finally predicted extinction risk in response to hypothetical forestry scenarios (Chapter 3). In Chapter 1 we estimated one of the requisite parameters for the model, juvenile survival, based on 8 years of field data. We estimated juvenile survival probabilities (to first breeding) at 17% for males and 11% for females. To our knowledge, these are the first estimates for marbled salamanders that include both returning and dispersing individuals. In Chapter 2 we used a metapopulation model to estimate extinction risk and sensitivity of extinction risk to changes in vital rates and other model parameters. We found that although there is considerable uncertainty in our estimate it is likely that extinction risk is low at our study site. Sensitivity analysis revealed that small changes in adult survival lead to relatively large changes in persistence and the presence of an apparent threshold in reproductive failure probabilities beyond which extinction risk rapidly increased. In Chapter 3 we used the extinction risk and sensitivity estimates to model the effects of forestry on the metapopulation. We parameterized several different levels of impact of forestry on salamander survival; for each parameterization we calculated the extinction risk for 20 different forestry scenarios involving buffer size (30 to 300 meters) and complete or partial restrictions on cutting (5 different levels). We found for all but the most optimistic parameterizations large buffers (around 200 meters) with high restrictions on cutting within the buffer were necessary to maintain a low extinction risk. Overall we show that although the population at our intensively studied field site is unlikely to go extinct under present conditions small decreases in adult survival, small increases in catastrophe rate, and intensive forestry can all make extinction likely.

Eastern hemlock (Tsuga canadensis) is in decline because of infestation by the invasive hemlock woolly adelgid (Adelges tsugae; ‘HWA’) and, to a lesser extent, the elongate hemlock scale (Fiorinia externa; ‘EHS’). Many conifers respond to insect herbivory by inducing oleoresin-based defenses, however it is unknown whether eastern hemlock is capable of this inducible response. We conducted a plantation setting study of artificially infested saplings to determine if feeding by HWA or EHS induces changes in the tree’s volatile chemistry. The induced changes in volatiles we found were unlike the terpenoid-based defenses of related conifers. Only HWA feeding elevated methyl salicylate, a plant signal for systemic acquired resistance, and benzyl alcohol, a known antimicrobial and aphid deterrent. The influence of environmental conditions and tree life-stage on hemlock volatile chemistry, potentially important factors for wild hemlock populations, is unknown. We investigated whether mature and immature forest trees respond to HWA infestation with the same patterns of volatile production as plantation saplings in full sun and amended soils. HWA induced volatile changes comparable to those of plantation saplings, with many-fold benzenoid increases and no terpenoid-based resinosis. Nearly all volatiles were substantially more abundant in forest than plantation trees, suggesting the effect of site conditions should be addressed in investigations of mechanisms operative in HWA-resistant biotypes of eastern hemlock. Our findings represent the first important step toward understanding the influence of inducible phytochemical responses on hemlock susceptibility to exotic pests, and highlight the possibility of salicylic acid-dependent biosynthetic activity in this gymnosperm system.

Developing quantified establishment period estimates for newly planted trees will help set realistic goals for plant performance in the urban landscape. Nine years of tree planting records obtained from the city of Boston, MA and the town of Brookline, MA were used to derive samples of trunk caliper for hedge maple (Acer campestre), London planetree (Platanus x acerifolia), and red oak (Quercus rubra). Several site characteristics were measured to identify effects on newly planted tree growth. Breakpoint estimates of the piecewise regression models fell at 4 years and 6 years for London planetree and hedge maple respectively, showing establishment periods for urban trees are longer than the conventional 3 years. Pit area has a significant effect on caliper growth for London planetree and red oak, with larger growing spaces yielding larger trees. Observed soil bulk densities did not have a significant effect on caliper measurement for any of the species tested. Mean soil bulk density was 1.4 g/cm3, 1.45 g/cm3, and 1.49 g/cm3 for hedge maple, London planetree, and red oak respectively. Soil texture was significant for hedge maple only, with percent clay showing significant positive effects and percent sand as marginally significant. Pit type showed a significant effect on caliper measurement of London planetree with grass strips producing the largest caliper trees followed by open pits. Planting locations with tree grates produced the smallest caliper trees. Presence of perforated air vents produced significantly larger caliper trees than sites with an air vent present for red oak.

Numerous studies have evaluated the relationship between biodiversity and productivity, with general trends suggesting a positive relationship. While most studies only use species richness, this study also analyzed how productivity changes with functional diversity and Shannon’s diversity index. Functional diversity gives important context to the examination of biodiversity-productivity relationships due to the direct link between organisms’ functional traits and their role in a given ecosystem. This study used data from the USDA Forest Service Forest Inventory and Analysis (FIA) database collected in Alabama, Louisiana, and Mississippi to estimate plot-level productivity and diversity. Structural equation modeling was used to determine the strength of the relationship between measures of diversity and forest productivity. This study found that species richness had the greatest influence on forest productivity, but it was largely an indirect effect mediated by stand density. This study could be expanded spatially to include more forest types for comparison of trends.

Among exotic species that are capable of invading, establishing, and reaching pest status, few pose the range of impacts to biotic (e.g., competition with native species, predation, herbivory, introduction of other exotics) and abiotic (e.g., soil, hydrology) ecosystem components that can be attributed to the wild pig (Sus scrofa). Despite the presence of wild pigs throughout the southeastern United States for centuries, new invasions continue to occur in previously uninhabited and often under-investigated landscapes, including bottomland and upland forests. The recent invasion of the Sam D. Hamilton Noxubee National Wildlife Refuge (hereafter, NNWR) in east-central Mississippi represents an opportunity to understand not only a species invasion during an emergent stage, but also to improve and better inform the methods used to combat such species in forested landscapes. In recent years, the United States Fish and Wildlife Service has begun to observe direct impacts to this ecologically sensitive area which is critically important to not only migratory waterfowl but also a multitude of other faunal (e.g., amphibians, reptiles, and avian species of concern) and floral species. As a result, identifying wild pig spatial distributions (e.g., movements, occurrence) and estimating wild pig abundance in the NNWR have each increased in priority. My dissertation research has facilitated an improved understanding of how wild pigs have invaded this novel landscape through investigations of space use, abundance, and occurrence, and will better inform and improve efficiency of future monitoring and control efforts. Understanding how this wild pig invasion relates to the NNWR landscape may also provide information that can be used to better address wild pig invasions of similar landscapes, with added value for those that are similarly characterized by sensitive ecosystems (i.e., managed for migratory waterfowl, species of concern) that are currently faced with this emerging threat. Given the universality of many of the methodological approaches undertaken in this effort, this multifaceted investigation also provides broader implications for other landscapes and exotic species of interest.

ABSTRACT Classifying and Mapping Diversity in a Species-Poor System: the mangrove meta-community of Laguna Chacahua National Park, Oaxaca, Mexico by Elizabeth Kay Weisgerber Both field transects and imagery grid plots were analyzed with the goal of creating a community classification map for the mangrove forest of Parque Nacional Lagunas de Chacahua. In total, data was collected in 49 sites throughout the park, recording measures such as DBH, basal area, estimated dominance, frequency, cover and relative dominance. Field locations were marked and georeferenced with a GPS and grid plots overlaid on satellite imagery of the park were generated via a random number table. Species' attributes delineating the identifiable features for each dominant species within Chacahua were noted and used to recognize patterns in species assemblages. Fourteen distinct ‘sub-communities’ within the mangrove meta-community were recognized using this data and verified with 165 field photos. Relative dominance values were compared between field and grid data. These data revealed a similar pattern with Rhizophora mangle being most dominant under each method. Avicennia germinans was second in relative dominance, Laguncularia racemosa a close third while Conocarpus erectus was rarely found, most likely due to over-harvesting. Rapid degradation of mangrove forests is occurring on a global scale. Understanding the complex dynamics that occur within the mangrove meta-community is essential to its conservation. Vegetation maps are essential tool in monitoring changes throughout the mangrove but are rarely of sufficient detail for everyday use. Generating highly detailed vegetation maps in a cost-effective and timely manner is an important step for their conservation, particularly in developing countries. This study demonstrates methods and techniques for producing a vegetation map that portrays the level of complexity that exists within the species-poor mangrove environment. This map will be donated to the management team of Parque Nacional Lagunas de Chacahua to better aid in management.

It is widely accepted that allelopathy is not only significant, but more or less singular, in the inhibition of understory vegetation in California Eucalyptus globulus (blue gum) plantations. However, there is no published documentation of allelopathy by blue gums against California native species. Here, we present evidence that germination and early seedling growth of five California native species are not inhibited by chemical extracts of blue gum foliage, either at naturally-occurring or artificially concentrated levels. In the greenhouse, seeds were germinated in field-collected soil from mature blue gum plantations and the adjacent native, coastal scrub communities. In petri plates, seeds of native species were germinated in the presence of concentrated volatile and water-soluble compounds from fresh foliage of blue gum, coast live oak (Quercus agrifolia) as a negative control, or white sage (Salvia apiana) as a positive control, or in a water control. In the greenhouse, blue gum soil supported germination and early seedling growth of native species equal to or better than coastal scrub soil. In the lab, germination of native species was not inhibited when grown in the presence of volatile compounds from blue gum foliage, compared to the native control (coast live oak) or the neutral water control. Germination of three out of five native species tested was not inhibited in the presence of water-soluble compounds from blue gum foliage, compared to coast live oak or the water control. Our results contradict the long-standing paradigm that blue gums are toxic to California natives, which may have significant implications for management and restoration of land historically occupied by blue gum plantations.

Piratebush (Buckleya distichophylla (Nutt.) Torr.) is a rare, hemiparasitic shrub with the only extant populations in western North Carolina, northeastern Tennessee, and southwestern Virginia. The preferred natural hosts of piratebush, Carolina and eastern hemlocks, have seen sharp declines over the last decade due to the invasive hemlock woolly adelgid. Virginia pine, another important host of piratebush, is also susceptible to disease, specifically Cronartium appalachianum, a rust fungus for which piratebush is the secondary host. This study described and analyzed current demographic parameters of three Tennessee piratebush populations. Additionally, spatial patterns of disease and demographic characters were analyzed. These data were compared to data from previous censuses to infer the impacts of diseases on piratebush and its host. All three populations were relatively stable in numbers and age structure over the past thirty years. Plant height and stems per shrub were similar among populations and stable over time. Seedlings represented 14%-19% of populations and non-flowering plants 33%-41% of populations. Two populations had an equal sex ratio and one population was male-biased. Disease prevalence was similar among populations but disease was more severe at Temple Ridge. The effects of hemlock decline were most acute at the Temple Ridge population where areas of high hemlock decline were associated with lower vigor piratebush individuals. Piratebush individuals near Virginia pines were more likely to be infected by C. appalachianum, and individuals infected by the rust fungus were more likely to have lower vigor. If hemlock decline is causing a piratebush host shift toward Virginia pine, piratebush populations may also decline because of potential enhanced infection by C. appalachianum. Treatment to prevent HWA infestation may be needed because of its effectiveness in improving the health of both hemlock and piratebush populations.

Coastal forest retreat in the Florida Keys during the 20th century has been attributed to a combination of sea level rise and hurricane storm surge impacts, but the interactions between these two disturbances leading to forest decline are not well understood. The goal of my research was to assess their effects over a period spanning more than two decades, and to examine the relationships between these press and pulse disturbances and freshwater availability in pine rockland, hardwood hammock, and supratidal scrub communities. Impacts and recovery from two storm surges, Hurricanes Georges (1998) and Wilma (2005), were assessed with satellite-derived vegetation indices and multiple change detection techniques. Impacts were greater at lower elevations, and in hardwood hammock, spectral signatures indicative of plant stress and productivity returned to pre-disturbance levels within a few years. In pine rockland, impacts were predominately related to Hurricane Wilma, however, a similar return to pre-disturbance conditions was absent, suggesting that trajectories of disturbance recovery differed between the two communities. Long-term monitoring of forest composition, structure, and groundwater salinity showed that compositional shifts in the low shrub stratum were associated with salinization of the freshwater resource attributable to sea level rise. Throughout the course of twelve months of climate and groundwater monitoring (2011-2012), groundwater salinity generally decreased in response to large precipitation events. Modeling of geophysical data indicated that groundwater salinity was an important predictor of community type. Isotopic analysis of d18O in plant stem water and foliar d13C was used to determine temporal and spatial patterns in water use and plant stress in two community dominants, slash pine, Pinus elliottii var. densa, and buttonwood, Conocarpus erectus. Both species relied heavily on groundwater, and plant stress was related to increasing groundwater salinity. The results of this work suggest that the interaction of press and pulse disturbances drive changes in community composition by causing mortality of salt-sensitive species and altering the freshwater resource.

A botanical inventory of Doe Mountain Recreation Area (DMRA) in northeastern Tennessee was conducted to help guide conservation-based management. A total of 484 species were found in DMRA, comprising 94 families, and 285 genera, 10 species listed in the state rare plant list, and 76 exotic species. Two species, Liatris virgata and Lycopodiella inundata, were new state records. Water in the Lycopodiella seep was an order of magnitude more acid than at other sites. An analysis of the wildland-urban interface showed that only 13% of the area was classified as uninhabited. The inventory-invasion index, introduced to quantify the relative degree of botanical uniqueness, was indicative of an under-explored or unique area but less so compared to some other botanically-rich regional sites. Management should aim to protect acid seeps, arid roadside slopes, curtail mowing a roadside that supports a state endangered species, and avoid herbicides in the biodiverse power line corridor.