Forest Biology Commons^™

Patterns Of Fire History And Vegetation Changes In The Last 5000 Years: A Paleoecological Study Of Iquitos, Annabel Zwarts

Theses and Dissertations

The vegetation of the Amazonian rainforest is hypothesized to have been shaped by pre-Columbian activities, such as burning and palm management to various extents. Management of palms is hypothesized to have caused some of the most useful species to become hyperdominant in Amazonia. This study investigated the extent to which human activities over the past 5000 years affected palm abundances in mature lowland rainforests near Iquitos, Peru. I used phytoliths and charcoal from soil cores to determine the history of local floras, and modern palm surveys to compare modern phytolith occurrence with modern vegetation. Because pre-Columbian activity clustered along the …

Leaf To Canopy Functional Resilience: Plant Physiological And Carbon Cycling Stability Following Disturbances, Lisa T. Haber

Theses and Dissertations

Ecological disturbances impact core ecosystem functions, including production and biogeochemical cycling, by precipitating changes in biodiversity, physical environmental variables, vegetation structure, and functional trait distributions. As disturbance patterns intensify and abruptly transition to novel regimes under global change, future trajectories of ecosystem functions, including carbon (C) uptake and storage, are uncertain. A more complete understanding of the mechanisms underpinning ecosystem stability (or ability to return to baseline functioning) following disturbance is needed to forecast future C cycling.

Replicated ecosystem-scale disturbance experiments, particularly when coupled with modeling, are required to rigorously test hypothesized trajectories of ecosystem structural and functional change following …

Modeling The Effect Of Neighborhood Competition On Tree Diameter Growth In The Pacific Northwest Coast Range, Htet Lin Naing

Theses and Dissertations

Trees compete for various resources such as sunlight, water, and nutrients, which can be expressed as numerical terms, called competition indices (CI). Competition between individual trees is correlated with their growth and mortality. Therefore, CIs are used as independent variables to develop, improve and modify growth and yield models. This study was conducted to test the effect of neighborhood competition on tree diameter growth among Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg) and red alder (Alnus rubra Bong.), in the Pacific Northwest Coast Range, USA. After testing seven distance-independent CIs and three distance-dependent …

Gene Expression Effects On Productivity And Stress Tolerance In Polyclonal Plantings Of Populus Deltoides, Macy Gosselaar

Theses and Dissertations

Polyclonal plantings of Populus deltoides are expected to display increased site resource use, productivity, and tolerance to stress through plasticity changes leading to niche differentiation (i.e changes to crown/canopy structures). In the present study, P. deltoides Clones S7C8, 110412, and polyclonal plots were tested for differentially expressed genes and enriched biological pathways between planting schemes. Transcriptomic analysis of leaves revealed upregulation of an active growth gene and gene family members that play important roles in plant stress and stress tolerance in polyclonal plantings. A gene associated with oxidative stress was upregulated in polyclonal plantings across all treatments. Secondary metabolic pathways …

A Four-Pronged Approach To Addressing A Wild Pig Invasion In A Bottomland And Upland Forested Landscape, Tyler Scott Evans

Theses and Dissertations

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 …

Patterns, Mechanisms, And Characterization Of Carbon Cycling Stability Following Partial Forest Disturbance, Kayla C. Mathes

Theses and Dissertations

Among the most essential questions in the era of climate change is how the forest carbon (C) cycle will respond to an increase in the extent of biotic disturbances from insects and pathogens. While research has focused on stand-replacing disturbance regimes, less is known about C cycling stability following partial disturbances that produce gradients of disturbance severity. Belowground C cycling responses to disturbance are especially poorly understood, even though temperate forest soils contain up to 50% of total ecosystem C and soil respiration (R_s) accounts for more than half of temperate forest C loss. Interpreting trends and mechanisms …

Diversity-Productivity Relationships In Forests Of The Southeastern United States: Leveraging National Inventory Data And Tree Functional Traits, Elizabeth Baach

Theses and Dissertations

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 …

Climate Sensitive Diameter Growth Models For Major Tree Species In Mississippi, Sujan Subedi

Theses and Dissertations

Anticipated climate change and increasing wood demand require dependable diameter growth models for adaptive forest management. We used a mixed-effects modeling approach with Forest Inventory and Analysis (FIA) data to fit diameter growth models for loblolly pine, other softwood species (slash pine, shortleaf pine, and longleaf pine), sweetgum, and other hardwood (southern red oak, red maple, and water oak) species. Climatic variables coupled with individual tree attributes and competition factors improved climate insensitive models. Growth of loblolly pine and sweetgum was positively correlated with mean temperature of the coldest month. Mean temperature of the warmest month negatively influenced diameter growth …

Coupled Structure-Function Responses To Disturbance: High Structural Complexity Resistance Supports Primary Production Resistance, Kerstin M. Niedermaier

Theses and Dissertations

The capacity of forests to resist structural change and retain material legacies–the biotic and abiotic resources that persist through disturbance–is crucial to sustaining ecosystem functioning after disturbance. However, the role of forest structure as both a material legacy and feature supporting carbon (C) cycling stability following disturbance has not been widely investigated. We used a large-scale disturbance manipulation to ask whether LiDAR-derived canopy structures as material legacies drive 3-year responses of NPP to a range of disturbance severity levels. As part of the Forest Resilience Threshold Experiment (FoRTE) in northern Michigan, USA we simulated phloem-disrupting disturbances at a range of …

Advancing Forest Structure-Function Relationships: Linking Above- And Belowground Structure To Soil Respiration, Laura J. Hickey

Theses and Dissertations

Variation in the soil-to-atmosphere C flux, or soil respiration (Rs), is influenced by a suite of biotic and abiotic factors, including soil temperature, soil moisture, and root biomass. However, whether canopy structure is tied to soil respiration through its simultaneous influence over these drivers is not known. We assessed relationships between measures of above- and belowground vegetation density and complexity, and evaluated whether Rs is linked to remotely sensed canopy structure through pathways mediated by established biotic and abiotic mechanisms. Our results revealed that, at stand-scale, canopy rugosity–a measure of complexity–and vegetation area index were coupled to soil respiration through …

Forest Structure, Above-Ground Carbon Stocks, And Productivity Along An Elevational Gradient In The Ecuadorian Andes, Esteban Pinto

Theses and Dissertations

The Andean forest provides a natural laboratory for evaluating long-term interactions between forests and variation in environmental parameters along elevational gradients. In particular, the mechanisms that control above-ground carbon stocks (AGC) and natural dynamics in mountain ecosystems constitute a potentially powerful tool for understanding the function of these ecosystems and their response to current climate change scenarios or past human disturbances. The present study integrates biotic (rarefied species richness and leaf traits) and abiotic (climate, soil properties and degradation) factors as possible drivers of AGC stocks, AGC net change (AGCnt), AGC productivity (AGCp) and AGC mortality (AGCk), along an elevational …

A Spatiotemporal Assessment Of Fish Assemblage Response To Land-Use Change And The Evaluation Of Edna Metabarcoding For Describing Diverse Fish Communities, Timothy M. Owen

Theses and Dissertations

Fish assemblages are often assessed as a biological proxy for environmental health. While humans value healthy environments for the ecosystem services and recreational opportunities they provide, it is increasingly evident that such resources can be paradoxically degraded by anthropogenic activities. In this investigation, we studied the relationship between different intensities of anthropogenic land-use change and habitat-driven fish assemblage response across multiple spatiotemporal scales. Secondarily, we explored the efficacy of eDNA metabarcoding against conventional electrofishing techniques for the purpose of describing complete fish communities. This study was conducted in the Tuckahoe Creek basin near Richmond, Virginia. This James River tributary serves …

Senescent Trees Stabilize Aboveground Wood Net Primary Production Immediately After Disturbance, Maxim S. Grigri

Theses and Dissertations

In the United States, forests sequester 17% of national carbon (C) emissions annually (UGCRP, 2018), however shifting forest disturbances threaten the stability of this essential C sink. Unlike the high severity, stand-replacing disturbances that were widespread a century ago, today’s eastern temperate forests experience frequent low-to-moderate severity disturbances from invasive pests and pathogens with mixed effects on net primary production (NPP). Carbon cycling stability after disturbance has been reported, however, the mechanisms underlying immediate NPP stability or decline are not well understood. Through weekly measurements of production in a landscape scale experiment, we show that the sustained growth of senescent …

Forest Structural Complexity And Net Primary Production Resilience Across A Gradient Of Disturbance In A Great Lakes Ecosystem, Lisa T. Haber

Theses and Dissertations

Forests are an important component of the global carbon (C) cycle and contribute to climate change mitigation through atmospheric C uptake and storage in biomass and soils. However, the forest C sink is susceptible to disturbance, which modifies physical and biological structure and limits spatial extent of forests. Unlike severe, stand-replacing disturbances that reset forest successional trajectories and may simplify ecosystem structure, moderate severity disturbances may instead introduce complexity in ways that sustain net primary production (NPP), leading to the phenomenon of “NPP resilience.” In this study, we examined the linkage between disturbance severity and ecosystem biological and physical structural …

The Effects Of Disturbance And Species Specific Interactions On Diversity In An Agent Based Forest Simulation, Matthew E. Mills

Theses and Dissertations

In ecology literature, there is much data which suggests that conspecific negative density dependence (CNDD) and abiotic disturbances increase biodiversity in forests. This thesis elucidates the notion that not only do these two forces increase diversity, but they may also interact with one another in order to achieve higher levels of biodiversity. Abiotic disturbances, like fires and hurricanes, can indirectly impact conspecific effects because when these forces remove individuals from the landscape, the role of the conspecific effects will change. The interaction of these two factors in biodiversity are explored in an agent based forest simulation through a resource surface. …

Phylogenetic Analyses Of Andean And Amazonian Tree Communities In Ecuador, Samantha J. Worthy

Theses and Dissertations

The forests of Ecuador are known for their high levels of diversity and endemism, classifying the country as a biodiversity hotspot. Both the western Amazon and Andean montane forests are richly populated with tropical tree species that have been little studied in a community phylogenetic context. The implementation of elevational transects and trait based analyses having proven useful in gaining a better understanding of how environmental factors are affecting the tree community structure in these habitats. The goal of this research was to evaluate the magnitude ofDNA barcode diversity among Amazonian and Andean tree species. Specifically, the objectives were to …

Forest Stand Structure And Primary Production In Relation To Ecosystem Development, Disturbance, And Canopy Composition, Cynthia M. Scheuermann

Theses and Dissertations

Temperate forests are complex ecosystems that sequester carbon (C) in biomass. C storage is related to ecosystem-scale forest structure, changing over succession, disturbance, and with community composition. We quantified ecosystem biological and physical structure in two forest chronosequences varying in disturbance intensity, and three late successional functional types to examine how multiple structural expressions relate to ecosystem C cycling. We quantified C cycling as wood net primary production (NPP), ecosystem structure as Simpson’s Index, and physical structure as leaf quantity (LAI) and arrangement (rugosity), examining how wood NPP-structure relates to light distribution and use-efficiency. Relationships between structural attributes of biodiversity, …