How does saltwater intrusion impact the terrestrial ecosystems of the coastal plain of North Carolina
Climate change is transforming the outer edge of the Southern US coastal plain. Lower-lying parts of this region, characterized by extensive freshwater-dependent ecosystems, will be largely inundated by gradual sea level rise by the end of this century. In the interim, however, ocean waters are already penetrating and influencing freshwater-dependent coastal landscapes due to a combination of human and natural factors. This landward movement of salinity from the coast onto the coastal plain or “saltwater intrusion” represents the leading edge of climate change for many coastal landscapes. The salinization of surface waters and adjacent lands may lead to significant reductions in crop and timber yields in managed ecosystems, significant declines in ecosystem carbon sequestration in unmanaged ecosystems, and degradation of coastal water quality due to extraction of soil nutrients by seasalts. As this region and similar regions worldwide transform in response to and, indeed, in advance of rising seas, the sustainability of these coastal landscapes, now and for decades to come, hinges largely on a sophisticated understanding of the coupled human and natural processes influencing salinization of surface waters and adjacent lands. This project focuses specifically on saltwater intrusion across the Albemarle-Pamlico peninsula of North Carolina, and it will accomplish the 3 primary goals of NSF Coastal SEES: First, the project will provide a comprehensive toolset to enable place-based, system-level understanding of coastal systems at multiple spatial and temporal scales. Second, it will yield outcomes with predictive value in coastal systems that are easily understood by stakeholders while representing complex interactions between climate, hydrology, land use, and ecological processes. Third, by focusing on how information influences individual preferences, the project will identify pathways by which outcomes could be used to enhance coastal sustainability. Together, these activities will help guide sustainable management of this region and similarly affected regions over the next several decades to centuries.
What are the ecological consequences of intraspecific trait variability?
Stemming from our research on the ecological impacts of changes in fire frequency (see below), we became interested in trying to understand who species with large differences in rates of intraspecific variability in key leaf traits differ in their response to variable conditions. We are taking advantage of one of the largest existing (and continuing) databases on plant traits to ask questions about whether species with higher levels of trait variability have more stable demographic parameters across years and environments and whether this stability scales up to greater stability at the ecosystem level
What determines community composition and function when microbial communities collide?
The tiniest forms of life – microorganisms – encompass most of the diversity on Earth. Microbes are responsible for maintaining the function of various ecosystems, such as in the gut, soil, and in water, yet little is known about what controls where microbes live, and how they respond to changes in local conditions. A tree – a type of macro-organism - exists in a given location if it can survive both the environmental conditions (abiotic factors) and interactions with its neighbors (biotic factors), and its seedlings may disperse to new locations with new environmental conditions. Unlike trees, microbes frequently migrate as whole communities and in tandem with their environment, often merging with other microbial communities along with their respective environments. For instance, wind movement of soil particles across the landscape or human handshakes result in novel contact of previously separated microbial communities – this is termed community coalescence. The confluence of two water bodies is a clear example of community coalescence, resulting in a new, united environment with novel interactions among the previously separate microbial communities, yet little is known about how these communities interact and respond to the merger.
Therefore, the goal of this project is to understand how microbial communities from distinct habitats interact under community coalescence, with the following specific objectives: (1) Characterize the membership of microbial communities in the field as well as their activity at three distinct aquatic environments where coalescence occurs, (2) In the laboratory, track microbial community membership and activity in response to experimentally-imposed coalescence, and (3) Analyze the experimental data in the context of the patterns observed in the field. The researchers will address these objectives using three aquatic environments where community coalescence occurs: Salinity: seawater intrusion of coastal wetland, Nutrients: a thermally-stable spring flowing into a blackwater river, and Temperature: a hot spring flowing into a cooler mountain stream. Unraveling the mechanisms that determine community membership following a coalescence event is difficult, since the abiotic and biotic factors are often intertwined. In order to understand the true community ecology of microbes, it is necessary to separate the environmental and biological factors that ultimately determine which organisms persist and which do not. To address these fundamental ecological questions, the research team developed a new approach to directly measure the effects of environmental factors and biotic interactions, independently and in combination, on resultant communities. This novel project tackles fundamental concepts in community ecology, addressing dispersal of a massive number of microorganisms in the context of aquatic systems, and will also serve to directly disentangle biotic and abiotic factors, which remains a forefront issue in community ecology.
Previous projects - no current funding, but I'm always interested in thinking more about these things!
The links between biodiversity and ecosystem functioning
In addition to understanding what controls the distribution of biological diversity, I am interested in understanding how variability in diversity affects ecosystem functioning. In my work with BioMERGE, I took a lead role in trying to synthesize much of the conflicting results from this broad field of science as well as push the field into new and productive areas. In particular, I have focused my work on the following areas:
Understanding the role of functional diversity in controlling ecosystem functioning - how do we measure functional diversity? Do commonly used functional groups work? Do functional classification schemes based on global patterns apply to smaller scale variability in ecosystem functioning?
How do we scale up from the small-scale experimental results to predict the effects of biological diversity on ecosystem functioning at spatial scales relevant for management?
How do we incorporate higher trophic levels into our models which are primarily plant based?
Much of my efforts in this area are focused on a large-scale biodiversity experiment that combines a field experiment at a wetland restoration site with an intensive study of the distribution and plasticity of the morphological and physiological traits likely to influence ecosystem functioning among a long list of herbaceous species recommended for use in wetland restoration projects in the state of North Carolina.
Succession across a Latitudinal Gradient Network (SLaGNet)
Collaborator: Dr. Jason Fridley, Syracuse University
This experiment explores the patterns and process of ecological succession, the sequence of communities from initial colonization to climax communities. Old fields in the Northeast U.S. can persist for decades in an herbaceous state, while those of the Southeast U.S. typically support closed pine canopies in less than a decade. We seek to identify the significant drivers of this latitudinal pattern of natural old-field woody invasion across the Eastern Deciduous Forest (EDF), and determine whether predicted climate change will significantly influence the rate at which ecological communities transition from herbaceous- to woody-dominated ecosystems. We will specifically investigate the influence of climate, soil fertility, and species pool by isolating each of these variables. We will use our results to predict whether a warmer climate will change the structure of the EDF by altering the persistence of herbaceous-dominated communities in the current forest-field mosaic.
Climate-sensitive thresholds of competitive balance between growth forms suggests the influence of climate on the rate of succession could result in accelerated movement of early successional tree species northward by promoting the competitive advantage of colonizing trees over herbaceous perennials. However, if herbaceous-dominated communities persist in the NE for reasons other than climate, such as soil fertility or the identity of key species, then northward migration of early successional trees could lag substantially. To address these questions, we have selected six old fields study sites across the full latitudinal gradient of the EDF from Syracuse, NY to Tallahassee, FL. at each site woody pioneer species' seeds with N and S provenances will be planted on ambient and control soils, with and without interference from two types of perennial old-field herbaceous communities.
Nutrient Network (NutNet)
International collaboration, Local collaborator: Dr. Charles Mitchell, UNC
Human activity has a range of impacts on ecosystems. The Nutrient Network (NutNet) focuses on two impacts. First, fossil fuel combustion and agricultural fertilization have doubled and quintupled, respectively, global pools of nitrogen and phosphorus, relative to pre-industrial levels. This has altered the global nutrient budget. Nitrogen and phosphorus often stimulate plant growth, potentially impacting the rest of the food web. Second, habitat loss and degradation, and selective hunting and fishing, remove consumers from food webs. Consumers include both carnivores and herbivores � species like deer that consume plants. At the same time, humans add consumers to food webs for conservation, recreation, and agriculture, as well as by accidental introductions of invasive consumer species. These activities have changed the abundance and identity of consumers. In spite of the global impacts of these human activities, there have been no globally coordinated experiments to quantify their impacts on ecological systems. The NutNet is a grassroots research effort to investigate these ecological impacts within a coordinated research network comprised of more than 40 grassland sites worldwide. Each NutNet site includes thirty square plots, each of which is 5 meters (about 16 feet) on a side. A nutrient addition treatment was randomly assigned to each plot. The fences were built as a second treatment to exclude herbivores from those plots. These treatments are designed to simulate human-caused global changes. Each year, we determine soil nutrient concentrations, plant biomass, and plant species identity to understand how increased nutrient budgets and changes in consumer populations will impact the ecosystem. For more information on the entire Nutrient Network visit their website here.
Cross-scale assessment of ecological resilience to altered fire regimes
Given the critical role that fire plays in controlling the distribution of plant species and functioning of ecosystems, predicting changes in these processes in response to changes in fire regime is a key problem facing ecology. The problem is complicated by the fact that species have highly individualistic responses to fire and furthermore by the feedbacks that exist between plant composition and fire behavior. These challenges call for a trait-based approach that looks for common drivers across species of responses to and effects on fire that allow for greater generalization than a species-based approach. We will develop such an approach to predict how vegetation composition and structure will change along gradients from upland Longleaf Pine Savannas to Streamhead Pocosins under different prescribed burning regimes at Fort Bragg, North Carolina.
While the proposed research has exciting implications for basic ecological questions, it will also provide important tools for management of fire-dominated ecosystems. An emphasis on identifying thresholds of change will help inform decisions about the strategic application of prescribed fire under increasing restrictions on its use. Given the extensive use of prescribed fires on Department of Defense facilities, such information fills a critical need as managers develop burn regimes that meet all statutory and regulatory requirements as well as ecological and sociological goals.