Browsing by Subject "Forestry"
- Results Per Page
- Sort Options
Item Open Access A MULTIVARIATE ASSESSMENT OF THE CONNECTICUT LAKES FOREST ECOSYSTEM , NH(2007-05) LaPlante, SarahFollowing 100 years of intense timber harvest and in the face of potential future development, the northeastern forest ecosystem is in a period of transition. To protect forest biodiversity, wildlife habitat, water quality and recreational needs, New Hampshire Fish and Game (NHFG) acquired 25,000 acres of this forest in 2002. With the intent of tracking change and management progress in this complex ecosystem, NHFG is currently designing a monitoring program to implement in the near future. This document applies ordination techniques to analyze both forest structure and forest species composition in an attempt to compare the state of the current forest with its future potential forest type. Techniques applied here can guide the design of future monitoring efforts. Forest structure variables were analyzed using a principal components analysis (PCA) and forest species composition variables were analyzed with a non-metric multidimensional scaling (NMS) technique. Species composition was further examined to search for distinct clusters in the NMS ordination. Current forest structure was found to be similar for all plots, regardless of their future forest potential. It is possible that either past harvesting in this region diminished natural variation between forest types, or that differences within forest types are greater than those between forest types. Current forest species composition analysis revealed that there are subtle differences between plots based on species composition, but that those differences did not align by potential forest type. Existing differences are present through a gradient, not in distinct forest types. Further analysis and exploration of these techniques will give NHFG a practical, integrated tool to gauge health and track change in this complex ecosystem.Item Open Access ACE Basin National Wildlife Refuge Forest Inventory and Carbon Stock Analysis(2021-12-08) Murphy, Mary CarltonThe ACE Basin National Wildlife Refuge (NWR) is 11,815 acres of critical wildlife habitat in South Carolina’s Lowcountry region. The Refuge contains a mosaic of forest types, including upland pine and hardwood, bottomland hardwood, and cypress-tupelo swamps. Periodic forest inventories serve to update Refuge managers on current forest conditions and identify areas outside of desired forest conditions. Desired Forest Conditions (DFC) are defined forest composition and structure metrics representing critical wildlife habitat. Active forest management, including thinning and prescribed fire, is often used on NWRs to meet DFC metrics, and thereby promote and enhance wildlife habitat. This project consisted of a 10-week forest inventory field assessment of ACE Basin NWR to evaluate current forest conditions in relation to DFC metrics. A subsequent analysis quantified how potential forest management activities to achieve DFC metrics would affect carbon stocks. Project findings suggest that most Refuge forests are outside of desired conditions and require a suite of management activities to achieve optimal wildlife habitat. These activities, however, will reduce forest carbon stocks and this project suggests forest management practices that may address these tradeoffs.Item Open Access America’s Evolving Relationship with Trees: A Statistical Analysis of Social, Economic, and Environmental Drivers of Forest Management(2021) Holt, JonathanIn the spirit of American individualism, the majority of the United States’ forested landscape is controlled by private landowners, who make autonomous decisions that impact a shared wealth of biodiversity and ecosystem services. It is important to understand not only the forest management decisions made by private landowners, but also the motivations that incentivize these consequential actions. Furthermore, it is useful to have the capacity to infer such insights using publicly available data, and by employing transparent, flexible, and scalable statistical frameworks. This dissertation seeks to elucidate the motivations and actions of private landowners in the United States using a variety of data sources, including Zillow home estimates, the American Community Survey, satellite remote sensing imagery, and the Forest Inventory and Analysis database, and by implementing interpretable modeling frameworks, such as the hedonic pricing method and structural equation modeling. I uncover nuanced insights about human-environmental systems, including (1) a positive feedback loop between affluence and tree-shading in metropolitan areas; (2) the dominance of normative pressures on forest owners’ harvest intentions; and (3) a causal link between invasive insects and the quantity and sizes of harvested trees. Understanding such relationships benefits policymakers, forest managers, and urban planners tasked with optimizing human-natural systems.
Item Open Access Assessing Extent to Which US Southeastern Woody Biomass Supply Can Meet Renewable Electricity Demand in Present and Future Scenarios(2010-12-10) Cadigan, ChristineWoody biomass has rapidly come to the forefront of renewable energy discussions as a potentially reliable and affordable energy solution. The reason for such is rooted in international and domestic policy evolution. The increasing reliance on alternative energy options is a direct response to the desire for national energy security as well as a commitment to mitigate climate change. This project attempts to quantify the contribution of Southeastern forest resources to a proposed federal 15% Renewable Electricity Standard demand. Results indicate residual biomass supply can only provide 19% of a 15% RES demand under current population pressures and climate change conditions. More expansive biomass definitions increase the total biomass contribution, yet some of this supply requires unrealistic market expectations. Utilizing the more reasonable expansive supply, unused pulpwood capacity (peak production minus current production) provides, on average, an additional 8% to a 15% demand. Following initial calculations, biomass supply and electric demand were projected and estimated under future climate change scenarios for the state of North Carolina. Results of future projections suggest biomass can meet anywhere from 8- 17% of a 15% RPS demand. However, these are likely best-case scenarios, as climate change, demand for other products, and social acceptability for forest management all create uncertainties that will likely increase in the future. It is clear that biomass can only be a part of a renewable energy solution, at least in terms of offsetting traditional electric energy demand. Although biomass has the potential to be a significant contributor, policy makers must incorporate a flexible and diversified energy portfolio to establish complete RES compliance or recognize the increased efficiency of biomass in alternative energy applications.Item Open Access Changing the Paradigm: Inventory Review and Scenario Modeling for the Duke Forest(2017-04-28) Burrows, John; Burton, Harley; Hipp, TimothySince it was founded in 1931, the Duke Forest has shown a commitment to sustainable timber management practices and forestry education. However, in recent years, a misalignment between revenue expectations and the timber management paradigm have resulted in an uneven age class distribution favoring younger age classes of pine. The purpose of this project is help the Duke Forest address this management challenge by reassessing its inventory and yield projections from its 2010 inventory to understand how the Forest might be able to improve its estimation of sustainable harvest by more accurately accounting for volume growth. Additional analyses were also conducted to model different harvest rotation lengths using the US Forest Service’s Forest Vegetation Simulator (FVS) to understand how more intensive management practices, such as shortening the pine rotation length and planting genetically improved stock, could help balance the Forest’s age class distribution in other divisions while keeping the forest profitable.Item Open Access Climate Change and Forest Biodiversity in the Eastern United States: Insights from Inventory Data(2014) Zhu, KaiEcologists have long been interested in the relationships between climate change and forest biodiversity. For centuries, the scientific problems remain understanding the patterns of climate variation, forest geographic distribution, and demographic dynamics. Besides scientific merits, these questions will also help forest managers and policy makers to anticipate how forests respond to global change. This dissertation tackles these problems by using statistical modeling on climate and forest inventory data in the eastern United States.
In Chapter 1, we ask the question on the observed tree range distributions in response to contemporary climate change in the eastern United States. Tree species are expected to track warming climate by shifting their ranges to higher latitudes or elevations, but current evidence of latitudinal range shifts for suites of species is largely indirect. In response to global warming, offspring of trees are predicted to have ranges extend beyond adults at leading edges and the opposite relationship at trailing edges. Large-scale forest inventory data provides an opportunity to compare present latitudes of seedlings and adult trees at their range limits. Using the USDA Forest Service's Forest Inventory and Analysis data, we directly compared seedling and tree 5th and 95th percentile latitudes for 92 species in 30 longitudinal bands for 43,334 plots across the eastern United States. We further compared these latitudes with 20th century temperature and precipitation change and functional traits, including seed size and seed spread rate. Results suggest that 58.7% of the tree species examined show the pattern expected for a population undergoing range contraction, rather than expansion, at both northern and southern boundaries. Fewer species show a pattern consistent with a northward shift (20.7%) and fewer still with a southward shift (16.3%). Only 4.3% are consistent with expansion at both range limits. When compared with the 20th century climate changes that have occurred at the range boundaries themselves, there is no consistent evidence that population spread is greatest in areas where climate has changed most; nor are patterns related to seed size or dispersal characteristics. The fact that the majority of seedling extreme latitudes are less than those for adult trees may emphasize the lack of evidence for climate-mediated migration, and should increase concerns for the risks posed by climate change.
In Chapter 2, we ask the question on tree abundance within geographic range responding to climate variation in the eastern United States. Tree species are predicted to track future climate by shifting their geographic distributions, but climate-mediated migrations are not apparent in a recent continental-scale analysis (Chapter 1). To better understand the mechanisms of a possible migration lag, we analyzed relative recruitment patterns by comparing juvenile and adult tree abundances in climate space. One would expect relative recruitment to be higher in cold and dry climates as a result of tree migration with juveniles located further poleward than adults. Alternatively, relative recruitment could be higher in warm and wet climates as a result of higher tree population turnover with increased temperature and precipitation. Using the USDA Forest Service's Forest Inventory and Analysis data at regional scales, we jointly modeled juvenile and adult abundance distributions for 65 tree species in climate space of the eastern United States. We directly compared the optimal climate conditions for juveniles and adults, identified the climates where each species has high relative recruitment, and synthesized relative recruitment patterns across species. Results suggest that for 77% and 83% of the tree species, juveniles have higher optimal temperature and optimal precipitation, respectively, than adults. Across species, the relative recruitment pattern is dominated by relatively more abundant juveniles than adults in warm and wet climates. These different abundance-climate responses through life history are consistent with faster population turnover and inconsistent with the geographic trend of large-scale tree migration. Taken together, this juvenile-adult analysis suggests that tree species might respond to climate change by having faster turnover as dynamics accelerate with longer growing seasons and higher temperatures, before there is evidence of poleward migration at biogeographic scales.
In Chapter 3, we ask the question on the demographic dynamics of density dependence at the individual tree level in eastern US forests. Density dependence could maintain diversity in forests, but studies disagree on its importance. Part of the disagreement results from the fact that different studies evaluate different responses (per-seedling or per-adult survival or growth) of different stages (seeds, seedlings, or adults) to different inputs (density of seedlings, density or distance to adults). Most studies are conducted on a single site and thus are difficult to generalize. Using USDA Forest Service's Forest Inventory and Analysis data, we analyzed over a million seedling-to-sapling recruitment observations of 50 species for both per-tree (adult) and per-seedling recruitment rates, controlling for climate effects in eastern US forests. We focused on per-tree recruitment as it is most likely to promote diversity at the population level, and it is most likely to be identified in observational or experimental data. To understand the prevalence of density dependence, we quantified the proportion of species with significant positive or negative effects. To understand the strength of density dependence, we determined the magnitude of effects among conspecifics and heterospecifics, and how it changes with overall species abundance. We found that the majority of the 50 species have significant density dependence effects, mostly negative, on both per-tree and per-seedling recruitment. Per-tree recruitment is positively associated with conspecific seedlings, saplings, and heterospecific saplings, negatively associated with heterospecific seedlings, conspecific and heterospecific trees. Per-seedling recruitment is positively associated with conspecific and heterospecific saplings, but negatively associated with conspecific and heterospecific seedlings and trees. Furthermore, for both per-tree and per-seedling recruitment, density dependence effects are stronger for conspecific than heterospecific neighbors. However, the strength of these effects does not vary with species abundance. We conclude that density dependence is pervasive, especially for per-tree recruitment, and its strength among conspecifics and heterospecifics is consistent with the predictions of the Janzen-Connell hypothesis.
Item Open Access Conserving California’s Klamath-Cascade Using Spatial Climate Projections(2014-12-08) Fety, LaurenGlobal climate change complicates long-term conservation of forests. To be effective into the future, conservation efforts need to consider potential global change impacts and the ability of plants and animals to adapt. In northern California’s Klamath-Cascade region projected changes are heterogeneous across the complex landscape. Understanding future conditions can guide climate adaptation actions. The objective of this project is to support climate-smart conservation in the Klamath-Cascade through a spatially explicit analysis. The analysis searches for areas which have the highest likelihood of successful forest conservation in the uncertain future. In particular, the project looks at climate variability, tree species composition, and northern spotted owl habitat. It uses existing climate data and species envelope models to understand the long-term durability of the Klamath-Cascade. Within the region, it is likely that areas with smaller magnitudes of change will have future climatic conditions more favorable to species persistence. These areas are desirable for long-term conservation and protection of the plants and animals in the Klamath-Cascade. To identify areas desirable for species persistence, I used likelihood data from ten tree species climate envelope models to assess the similarity of current and future tree species composition. I also assessed the similarity of current precipitation and temperature variables to projected conditions. I found that many areas of the Klamath-Cascade will experience novel climate conditions by 2060. Some areas will experience considerably more warming and loss of precipitation than others. However, there are also significant portions of the region that have an overlap of current and future species climate envelopes, indicating similar current and future vegetation communities. I found that less than half of the areas identified for mature forest and northern spotted owl protection will remain in climatic conditions that are suitable. These findings can be helpful in identifying projects that are likely to sustain and conserve species of concern in the Klamath-Cascade.Item Open Access Costa Rica's payment for environmental services program: intention, implementation, and impact.(Conserv Biol, 2007-10) Sánchez-Azofeifa, G Arturo; Pfaff, Alexander; Robalino, Juan Andres; Boomhower, Judson PWe evaluated the intention, implementation, and impact of Costa Rica's program of payments for environmental services (PSA), which was established in the late 1990s. Payments are given to private landowners who own land in forest areas in recognition of the ecosystem services their land provides. To characterize the distribution of PSA in Costa Rica, we combined remote sensing with geographic information system databases and then used econometrics to explore the impacts of payments on deforestation. Payments were distributed broadly across ecological and socioeconomic gradients, but the 1997-2000 deforestation rate was not significantly lower in areas that received payments. Other successful Costa Rican conservation policies, including those prior to the PSA program, may explain the current reduction in deforestation rates. The PSA program is a major advance in the global institutionalization of ecosystem investments because few, if any, other countries have such a conservation history and because much can be learned from Costa Rica's experiences.Item Open Access Deadwood stocks increase with selective logging and large tree frequency in Gabon.(Glob Chang Biol, 2017-04) Carlson, Ben S; Koerner, Sally E; Medjibe, Vincent P; White, Lee JT; Poulsen, John RDeadwood is a major component of aboveground biomass (AGB) in tropical forests and is important as habitat and for nutrient cycling and carbon storage. With deforestation and degradation taking place throughout the tropics, improved understanding of the magnitude and spatial variation in deadwood is vital for the development of regional and global carbon budgets. However, this potentially important carbon pool is poorly quantified in Afrotropical forests and the regional drivers of deadwood stocks are unknown. In the first large-scale study of deadwood in Central Africa, we quantified stocks in 47 forest sites across Gabon and evaluated the effects of disturbance (logging), forest structure variables (live AGB, wood density, abundance of large trees), and abiotic variables (temperature, precipitation, seasonality). Average deadwood stocks (measured as necromass, the biomass of deadwood) were 65 Mg ha-1 or 23% of live AGB. Deadwood stocks varied spatially with disturbance and forest structure, but not abiotic variables. Deadwood stocks increased significantly with logging (+38 Mg ha-1 ) and the abundance of large trees (+2.4 Mg ha-1 for every tree >60 cm dbh). Gabon holds 0.74 Pg C, or 21% of total aboveground carbon in deadwood, a threefold increase over previous estimates. Importantly, deadwood densities in Gabon are comparable to those in the Neotropics and respond similarly to logging, but represent a lower proportion of live AGB (median of 18% in Gabon compared to 26% in the Neotropics). In forest carbon accounting, necromass is often assumed to be a constant proportion (9%) of biomass, but in humid tropical forests this ratio varies from 2% in undisturbed forest to 300% in logged forest. Because logging significantly increases the deadwood carbon pool, estimates of tropical forest carbon should at a minimum use different ratios for logged (mean of 30%) and unlogged forests (mean of 18%).Item Open Access Decoupling the effects of logging and hunting on an afrotropical animal community.(Ecol Appl, 2011-07) Poulsen, JR; Clark, CJ; Bolker, BMIn tropical forests, hunting nearly always accompanies logging. The entangled nature of these disturbances complicates our ability to resolve applied questions, such as whether secondary and degraded forest can sustain populations of tropical animals. With the expansion of logging in central Africa, conservation depends on knowledge of the individual and combined impacts of logging and hunting on animal populations. Our goals were (1) to decouple the effects of selective logging and hunting on densities of animal guilds, including apes, duikers, monkeys, elephant, pigs, squirrels, and large frugivorous and insectivorous birds and (2) to compare the relative importance of these disturbances to the effects of local-scale variation in forest structure and fruit abundance. In northern Republic of Congo, we surveyed animals along 30 transects positioned in forest disturbed by logging and hunting, logging alone, and neither logging nor hunting. While sampling transects twice per month for two years, we observed 47 179 animals of 19 species and eight guilds in 1154 passages (2861 km). Species densities varied by as much as 480% among forest areas perturbed by logging and/or hunting, demonstrating the strong effects of these disturbances on populations of some species. Densities of animal guilds varied more strongly with disturbance type than with variation in forest structure, canopy cover, and fruit abundance. Independently, logging and hunting decreased density of some guilds and increased density of others: densities varied from 44% lower (pigs) to 90% higher (insectivorous birds) between logged and unlogged forest and from 61% lower (apes) to 77% higher (frugivorous birds) between hunted and unhunted forest. Their combined impacts exacerbated decreases in populations of some guilds (ape, duiker, monkey, and pig), but counteracted one another for others (squirrels, insectivorous and frugivorous birds). Together, logging and hunting shifted the relative abundance of the animal community away from large mammals toward squirrels and birds. Logged forest, even in the absence of hunting, does not maintain similar densities as unlogged forest for most animal guilds. To balance conservation with the need for economic development and wild meat in tropical countries, landscapes should be spatially managed to include protected areas, community hunting zones, and production forest.Item Open Access Drone Use in Forestry 2021(2021-12-08) McElwee, ElisabethIn the last 20 years, advancements in technology, such as remote sensing, have facilitated improvements in forest management. The utilization of one remote sensing tool, in particular, an unmanned aerial vehicle (drone), has been gaining popularity in recent years. Drones provide an inexpensive alternative to aerial photos from a manned aircraft, providing quick access to high-resolution imagery, increased efficiency, reduced human risk, as well as a variety of other benefits. While there are many advantages to the use of drones in forestry and forest management, there are also limitations. These limitations are apparent when trying to apply methodologies across varying terrains, species compositions, and economic scales. Nevertheless, more people in forestry are beginning to explore the use of drones in forest management. In order to gain insight into the status and limitations of drone use in forest management in 2021, a nationwide survey targeted to those in forest management was developed and distributed. Ultimately the goal of this study is to provide a baseline for understanding how this technology is currently being used in forest management and to identify areas for improvement that may lead to greater utilization.Item Open Access Ecological and Financial Suitability of Sites for Long-Term Oak Management in Western North Carolina(2021-04-30) Scott, MichaelFor thousands of years, oak species have been the dominant canopy species in eastern and central United States hardwood forests. Oaks (Quercus spp.) provide myriad ecological services and arguably comprise the most valuable hardwood timber genus in the eastern US. In recent decades, however, research shows that oaks are declining in density and being outcompeted by fast growing species like yellow poplar (Liriodendron tulipifera) and red maple (Acer rubrum). Due to oak fire tolerance, and ability to withstand droughts and poor soil conditions, Quercus promises to be a vital genus for climate resiliency. Western North Carolina has historically supported expansive oak dominated forests, and organizations are now concerned about protecting this valuable ecosystem. This project sought to identify land in western North Carolina that is ecologically and financially suitable for oak management and to understand the following questions: 1) Where is oak management ecologically viable? 2) What is the financial potential for oak management? 3) Where can loggers access timber? This was accomplished by conducting a survey and literature review about logger accessibility in the mountains, creating an oak management prioritization map and GIS tool using logger data and oak ecological requirements, and a financial analysis of the profitability of oak silviculture prescriptions. The results will help The Nature Conservancy (TNC) identify high priority areas to initiate oak management systems. With careful planning, oak management can be financially viable in western North Carolina.Item Open Access Efficacy of Monitoring Management Activities in Longleaf Pine in North Carolina Using Remote Sensing(2019-12-10) Leung, EmilyUsing remote sensing as a tool to monitor forest management intervention may reduce the time and funds needed to actively visit landscapes. However, previous research typically studied the effects of large-scale disturbances, such as wildfires, to demonstrate the efficacy of using vegetation indices to track forest change. To better understand the limitations of these indices, Landsat 8 NDVI and NBRT values were calculated for 99 management units consisting of longleaf pine stands under stewardship of The Nature Conservancy of North Carolina. These units were across nine preserves held by TNC, in the Coastal Plain region of North Carolina. To assess change, indices values before and after management activity were compared, as well as indices values in management units with and without management intervention. These values were significant, but the changes were minimal. Linear mixed models were created to test the explanatory power that time since treatment, seasonality, treatment size, basal area, treatment type, and preserve locality had on the change in NDVI or NBRT. While these variables failed to explain the changes in indices values post-intervention, a variety of other factors may potentially express the reduction in NDVI or NBRT: other vegetative growth, climate variability, and the scale of the data may influence these indices’ results. As such, while the mixed models did not find these management characteristics explanatory, that alone does not reject the thesis that remote sensing may be useful for monitoring fine-scale change. Further study and extended data collection may prove useful.Item Open Access Four-decade responses of soil trace elements to an aggrading old-field forest: B, Mn, Zn, Cu, and Fe.(Ecology, 2008-10) Li, Jianwei; Richter, Daniel D; Mendoza, Arlene; Heine, PaulIn the ancient and acidic Ultisol soils of the Southern Piedmont, USA, we studied changes in trace element biogeochemistry over four decades, a period during which formerly cultivated cotton fields were planted with pine seedlings that grew into mature forest stands. In 16 permanent plots, we estimated 40-year accumulations of trace elements in forest biomass and O horizons (between 1957 and 1997), and changes in bioavailable soil fractions indexed by extractions of 0.05 mol/L HCl and 0.2 mol/L acid ammonium oxalate (AAO). Element accumulations in 40-year tree biomass plus O horizons totaled 0.9, 2.9, 4.8, 49.6, and 501.3 kg/ha for Cu, B, Zn, Mn, and Fe, respectively. In response to this forest development, samples of the upper 0.6-m of mineral soil archived in 1962 and 1997 followed one of three patterns. (1) Extractable B and Mn were significantly depleted, by -4.1 and -57.7 kg/ha with AAO, depletions comparable to accumulations in biomass plus O horizons, 2.9 and 49.6 kg/ha, respectively. Tree uptake of B and Mn from mineral soil greatly outpaced resupplies from atmospheric deposition, mineral weathering, and deep-root uptake. (2) Extractable Zn and Cu changed little during forest growth, indicating that nutrient resupplies kept pace with accumulations by the aggrading forest. (3) Oxalate-extractable Fe increased substantially during forest growth, by 275.8 kg/ha, about 10-fold more than accumulations in tree biomass (28.7 kg/ha). The large increases in AAO-extractable Fe in surficial 0.35-m mineral soils were accompanied by substantial accretions of Fe in the forest's O horizon, by 473 kg/ha, amounts that dwarfed inputs via litterfall and canopy throughfall, indicating that forest Fe cycling is qualitatively different from that of other macro- and micronutrients. Bioturbation of surficial forest soil layers cannot account for these fractions and transformations of Fe, and we hypothesize that the secondary forest's large inputs of organic additions over four decades has fundamentally altered soil Fe oxides, potentially altering the bioavailability and retention of macro- and micronutrients, contaminants, and organic matter itself. The wide range of responses among the ecosystem's trace elements illustrates the great dynamics of the soil system over time scales of decades.Item Open Access Linking Forest Restoration to Sustainable Value Chains with se.plan(2023-04-28) Caradine, Reed; Ezekiel, Micah; Piacsek, Gabriel; Wang, MeixinStumpage prices for timber can be low due to lack of demand for wood products, which threatens the sustainability of tree-growing projects. Prices can increase with more investment in local wood processing facilities and related infrastructure – the links in the value chain that would increase timber demand. se.plan, a geospatial tool built by the UN Food and Agriculture Organization (FAO) Forestry Division, helps investors find suitable locations for reforestation projects in emerging markets, but it does not have the capability to help find locations for wood processing facilities. Using Uganda as a case study, we augment the capabilities of se.plan and provide geospatial data to build a wood processing facility siting capability into the tool. To determine decision-making factors relevant to investments in reforestation and wood processing, we conducted a literature review and focus groups, and then we found and modified geospatial datasets relevant to those factors. We made recommendations on how FAO can incorporate the datasets into se.plan.Item Open Access Longterm Approaches to Assessing Tree Community Responses to Resource Limitation and Climate Variation(2011) Bell, David McFarlandThe effects of climate change on forest dynamics will be determined by tree responses at different life-stages and different scales -- from establishment to maturity and from individuals to populations. Studies incorporating local factors, such as natural enemies, competition, or tree physiology, with sufficient variation in climate are lacking. The importance of global and regional climate variation vs. local conditions and responses is poorly understood and may only be addressed with large datasets capturing sufficient environmental variation. This dissertation uses several large datasets to examine tree demographic and ecophysiological responses to light, moisture, predation, and climate in eastern temperate forests of North Carolina.
First, I use a 19-yr seed rain record from 13 forest plots in the piedmont, transition zone, and mountains to examine how climate-mediated seed maturation and density-dependent seed predation processes increase population reproductive variation in nine temperate tree species (Chapter 1). I address several hypotheses explaining interannual reproductive variation, such as resource matching, predator satiation, and pulse resource dynamics. My results indicate that (1) interannual reproductive variation increased as a result of seed maturation and seed predation processes, (2) seed maturation rates increased under warm, wet conditions, and (3) seed predation rates exhibited negative and positive density-dependence, depending of tree species and type of seed predator (specialist insects vs. generalist vertebrates). Because positive density-dependent seed predation dampened and negative density-dependent seed predation amplified the effects of climate-mediated maturation on reproductive variation, this study showed evaluations of tree reproduction need to incorporate both climate and seed predation.
Next, I use an 11-yr record of annual tree seedling growth and survival in 20 tree species planted in the piedmont and mountains to quantify individual tree seedling growth and survival responses to spatial variation in resources and temporal variation in climate (Chapter 2). First, I tested whether height-mediated growth provides an advantage to large individuals in all environments by amplifying responses to light and moisture or only when those resources were plentiful. Second, I tested whether allometric and survival responses differed among species based on life-history strategies. Individual height amplified tree seedling growth. However, some species exhibited amplification at moderate to high resource levels as well as depression of growth in large individuals growing in low light and moisture environments. Shade intolerant species exhibited an increasing ratio of height to diameter growth and increasing survival probability with both increasing light and moisture resources. Conversely, shade tolerant species exhibited decreasing height to diameter ratio with increasing light, possibly because of biomass allocation toward acquisition of limiting light resources. Despite relative small effects of drought and winter temperature of tree seedling demography, the results of this study indicate that individual tree seedlings sensitive to light and moisture environments, such as large seedlings and seedlings of shade intolerant species, growing in shaded or xeric sites may be particularly vulnerable to climate induced mortality.
Finally, I examine interannual and interspecific variation in canopy conductance using four years of environmental (vapor pressure deficit, above canopy light, and soil moisture) and stem sap flux data from heat dissipation probes for six co-occurring tree species. I developed a state-space modeling framework for predicting canopy conductance and transpiration which incorporates uncertainty in canopy and observation uncertainty. This approach is used to evaluate the degree to which co-occur deciduous tree species exhibited drought tolerating and drought avoiding canopy responses and whether these patterns were maintained in the face of interannual variation in environmental drivers. Comparisons of canopy conductance responses to environmental forcing across species and years highlighted the importance of tree sensitivity to moisture limitation, both in terms of high vapor pressure deficit and low soil moisture, and tree hydraulic characteristics within diverse forest communities. The state-space model produced similar parameter estimates to the more traditional boundary line analysis, performed well in terms of in-sample and out-of-sample prediction of sap flux observations, and provided for coherent incorporation of parameter, process, and observation errors in predicting missing data (i.e., gap-filling), canopy conductance, and transpiration.
Much needs to be learned about forest community responses to climate change, however these responses depend on local growing conditions (light and moisture), the life-stage being examined (seedlings, juveniles, or mature trees), and the scale of inference (individuals, canopies, or populations). Because climate change will not occur in isolation from other factors, such as stand age or disturbance, studies must characterize tree responses across multidimensional gradients in growing conditions. This dissertation addresses these challenges using large demographic and ecophysiological datasets well-suited for global change research.
Item Open Access Managing an Urban Preserve(2008-04-24T16:34:52Z) McPhee, ChristopherCoastal land tracts are being converted to development at an alarming rate in the United States. A prime example of this fact is the greater Myrtle Beach area in South Carolina where a single private land tract has remained undeveloped. This property was examined to comprehend how it has coped with the surrounding development and to provide support for retaining the stewardship attitude of the current landowner. The forest resources on the property were measured to uncover current weaknesses in the natural ecosystem. Weaknesses identified included deer overpopulation, compromised soil and water, and high fire risk. The information collected in the field provided a foundation for management recommendations that could resolve environmental and social problems. The property was split into seven management areas to best fit the diverse ecosystem types. Recommendations were provided for each individual area as well as for the whole property. These recommendations aimed to protect the property from encroaching development, mitigate environmental damages, advise on expansion and examine income-generating opportunities. Options were designed to fit all stated needs and assist in the overall preservation of this valuable ecological resource.Item Open Access Monitoring and Forecasting Forest Drought Stress to a Changing Climate(2017) Schwantes, Amanda MarieGlobally, trees are increasingly dying from extreme droughts and heatwaves, a trend that is expected to increase with climate change. Loss of trees has significant ecological, biophysical, and biogeochemical consequences. In this thesis, I explored how forests will respond to increases in droughts and heatwaves projected under climate change, by studying the impacts of the 2011 drought on the forests and woodlands of Texas. I first developed new methods using remote sensing that improved monitoring of forest disturbances from droughts and heatwaves at regional scales. I then explored multiple modeling approaches, to improve forecasts of forest vulnerability to future droughts and heatwaves.
Drought-induced tree mortality is unique because it often is limited to only subtle and diffuse changes in forest cover. Therefore, I first developed a new approach towards quantifying drought-driven canopy loss in open canopy woodland systems using remotely sensed imagery, across a Landsat scene in central Texas (>30,000 km2). I used classifications of 1-m orthophotos to calibrate and validate 30-m Landsat imagery. In scaling up to create regional canopy loss maps, I assembled a Landsat time-series and separated mortality pixels experiencing persistent canopy loss from pixels with only background noise by applying the Landtrendr algorithm. I then estimated percent tree canopy loss within each of these mortality pixels by comparing two models capable of handling zero-inflated continuous proportions: random forest and a zero-or-one inflated beta (ZOIB) regression model. I found that the ZOIB regression model had the highest accuracy in predicting canopy loss (mean absolute error = 5.16%, root mean square error = 8.01%).
Again using remotely sensed imagery, I developed a second method to quantify canopy loss due to the 2011 drought across the many diverse systems of Texas, from the eastern pine/hardwood forests to the western shrublands. I then used these maps to better understand which ecological systems were most impacted and climatic trends that could explain spatial patterns of canopy loss. Canopy loss observations in ~200 multi-temporal fine-scale orthophotos (1-m) were used to train coarser Landsat imagery (30-m) to create 30-m binary statewide canopy loss maps. I found that canopy loss occurred across all major ecoregions of Texas, with an average loss of 9.5%. The drought had the highest impact in post-oak woodlands, pinyon-juniper shrublands, and Ashe juniper woodlands. Focusing on a 100-km by ~1000-km transect spanning the State’s 5-fold east-west precipitation gradient (~1500 to ~300 mm), I compared spatially explicit 2011 climatic anomalies to our canopy loss maps. Much of the canopy loss occurred in areas that passed specific climatic thresholds: warm season anomalies in mean temperature (+1.6 °C) and vapor pressure deficit (VPD, +0.66 kPa), annual percent deviation in precipitation (-38%), and 2011 difference between precipitation and potential evapotranspiration (-1206 mm). Although similarly low precipitation occurred during the landmark 1950s drought, the VPD and temperature anomalies observed in 2011 were even greater. Furthermore, future climate data under the representative concentration pathway 8.5 trajectory project that average values will surpass the 2011 VPD anomaly during the 2070-2099 period and the temperature anomaly during the 2040-2099 period. Identifying vulnerable ecological systems to drought stress and climate thresholds associated with canopy loss will aid in predicting how forests will respond to a changing climate and how ecological landscapes will change in the near term.
As climate change continues, forest vulnerability to droughts and heatwaves is increasing, but vulnerability varies regionally and locally through landscape position. However, most models used in forecasting forest responses to heat and drought do not incorporate relevant spatial processes. Therefore, thirdly, to improve spatial predictions of tree vulnerability, I employed a non-linear stochastic model of soil moisture dynamics accounting for landscape differences in aspect, topography, and soils. Across a watershed in central Texas I modeled dynamic water stress for a dominant tree species, Juniperus ashei and projected future dynamic water stress through the 21st century. Modeled dynamic water stress tracked spatial patterns of drought-impacted area derived using remote sensing. Accuracy in predicting drought-impacted stands increased from 60%, accounting for only soil variability, to 72% when also including lateral redistribution of water and radiation/temperature effects attributable to aspect. Our analysis also suggests dynamic water stress will increase through the 21st century, with minimal buffering from the landscape. Favorable microsites/refugia may exist across a landscape where trees can persist; however, if future droughts are too severe, the buffering capacity of a heterogenous landscape could be overwhelmed. Incorporating spatial data will improve projections of future tree water stress and identification of potential resilient refugia.
Lastly, droughts impact tree species unequally and therefore have the potential to alter the species composition of forests. As droughts intensify under climate change, models that can account for both changing environmental conditions as well as joint species-specific responses are needed to forecast shifts in species ranges, composition, abundance, and mortality. Therefore, lastly, I used a Generalized Joint Attribute Model, GJAM, to simultaneously model live and dead basal area by species, across Texas, using Forest Inventory and Analysis plots from 2001-2015 and covariates related to climate, topography and soils. I then projected shifts in species abundance into the 21st century under multiple climate warming scenarios. Model projections show that many of the eastern hardwood species will likely shift eastward throughout the 21st century. Many of the western woodland species are also projected to shift eastward and become increasingly dominant throughout Texas. By modeling species abundance and mortality simultaneously and by using covariates related to climate variability, we can improve projections of forest responses to continuing climate change.
Item Open Access Multi-Objective GIS Analysis for Avoided Conversion Carbon Credits and Biodiversity Conservation(2019-12-06) Brantley, Matthew; Mize, Charles; Qiao, SunnyThis project develops a unique methodology in identifying individual tax parcels in North Carolina as possible locations for generating avoided conversion carbon offset credits, as well as including co-benefits such as ecological conservation and corridor viability. We used LiDAR canopy height data to estimate current and future carbon storage on each parcel, which were discounted based on their respective probability of conversion as determined by the randomForest statistical model. Conservation value was added to the carbon value in order to accommodate the multi-objective interests of our client, Duke Carbon Offset Initiative. The result of this project is a flexible GIS model that uses the three major inputs (carbon, conversion risk, conservation) to rank parcels for suitability based on the interests of the user. This unique method will help DCOI obtain their 2024 carbon-neutral goals for Duke University, protect key biodiversity areas, and set a framework for other academic institutions.Item Open Access Oil and gas projects in the Western Amazon: threats to wilderness, biodiversity, and indigenous peoples.(PLoS One, 2008-08-13) Finer, Matt; Jenkins, Clinton N; Pimm, Stuart L; Keane, Brian; Ross, CarlBACKGROUND: The western Amazon is the most biologically rich part of the Amazon basin and is home to a great diversity of indigenous ethnic groups, including some of the world's last uncontacted peoples living in voluntary isolation. Unlike the eastern Brazilian Amazon, it is still a largely intact ecosystem. Underlying this landscape are large reserves of oil and gas, many yet untapped. The growing global demand is leading to unprecedented exploration and development in the region. METHODOLOGY/PRINCIPAL FINDINGS: We synthesized information from government sources to quantify the status of oil development in the western Amazon. National governments delimit specific geographic areas or "blocks" that are zoned for hydrocarbon activities, which they may lease to state and multinational energy companies for exploration and production. About 180 oil and gas blocks now cover approximately 688,000 km(2) of the western Amazon. These blocks overlap the most species-rich part of the Amazon. We also found that many of the blocks overlap indigenous territories, both titled lands and areas utilized by peoples in voluntary isolation. In Ecuador and Peru, oil and gas blocks now cover more than two-thirds of the Amazon. In Bolivia and western Brazil, major exploration activities are set to increase rapidly. CONCLUSIONS/SIGNIFICANCE: Without improved policies, the increasing scope and magnitude of planned extraction means that environmental and social impacts are likely to intensify. We review the most pressing oil- and gas-related conservation policy issues confronting the region. These include the need for regional Strategic Environmental Impact Assessments and the adoption of roadless extraction techniques. We also consider the conflicts where the blocks overlap indigenous peoples' territories.