(1) 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 have taken 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.
(2) 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.
(3) 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.
(4) 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.