C-IC. Disturbance Regimes
Summary: Disturbance is an important driver of southern Appalachian ecosystem structure and function that interacts with human decision-making and environmental gradients.
Much of our previous research on ecosystem responses to disturbance focused on a subset of important forces acting on large scales and/or short-time intervals (e.g., the pattern and magnitude of wind damage in the Coweeta Basin from Hurricane Opal, (Hunter and Forkner 1999, Wright and Coleman 2002). We will be developing a comprehensive understanding of disturbance regimes for the region through three linked research projects focused on deriving disturbance signatures, probabilistic decadal land-use choice functions, and quantifying fluvial sedimentation patterns.
C-IC1. Dendro-ecological Analyses of Historic Disturbance Regimes
Summary: The distribution, diversity, and net primary productivity of southern Appalachian species represents the combined effects of environmental driving variables, natural disturbances (i.e., drought, insect damage, etc.), and human disturbances (i.e., logging, grazing, etc.).
Previous studies of forest composition in the Coweeta Basin (Elliott et al. 1999) indicate that only 50% of the variation in the distribution of vegetation is explained by site factors such as slope, aspect, and soils. Similarly, only 30 to 60% of ANPP (above-ground net primary productivity) variation across the landscape is explained by environmental driving variables (Bolstad et al. 2001). We hypothesize that human disturbance will account for a large portion of the remaining variation and once its proportional contribution is determined we can improve our ability to predict vegetation composition and ANPP.
Using dendroecological (tree ring)
techniques, we will seek answers to the following questions:
1. What are the signatures for local disturbance regimes in southern
Appalachian hardwoods over the last 100-200 years?
2. How much has local (small plot) disturbance regimes over the last
100-200 years affected current vegetation distribution and ANPP?
Investigators
Barry Clinton, USDA-USFS, Response to disturbance
Katherine Elliott, USDA-USFS, Plant
community ecology
Ted Gragson, University of Georgia, Human disturbance processes
Jennifer Knoepp, USDA-USFS, Soil Processes
James Vose, USDA-USFS, Forest Processes
Previous Research on Topic
C-IC2. Human-disturbance: Analyses of Land-use Choices
Summary: Human land-use choices are
the primary disturbance on private lands, which cover approximately 55% of
our study region.
Typical studies evaluate land use choice probabilities as a function of
physical measures of land quality (e.g., the Von Thünen model, Samuelson
1983, the Central Business District model, Capozza and Helsley 1989), but
must assume that social variables remain constant across the landscape.
Historical accounts of land use in the southern Appalachian Mountains
(e.g., Silver 1990, Salstrom 1994, Davis 2000) are similarly incomplete
because they seldom quantify impacts across time or evaluate their
heterogeneity across space. A probabilistic model of land-use choice
across the region will be derived for each decade from 1800 to the present
by using land use and property records, oral histories, geneology,
population and agricultural census records, and remote imagery.
The following questions will be
addressed:
1. What is the relation between land use choices and changing markets,
institutions and environmental conditions?
2. How do economic transitions over time relate to the nature and the
distribution of land conversion?
3. How do the costs and benefits of environmental policies affect the
spatial dimensions of land use decisions across time, and therefore the
storage of carbon or delivery of sediment to streams?
Investigators
Ted Gragson, University of Georgia, Human
disturbance processes
David Newman, University of Georgia, Forest Economics/Policy
David Wear, USDA-USFS, Forest Economic Modeling
Previous Research on Topic
C-IC3. Impacts of Historic Land-use on River Channels and Floodplains
Summary: The focus of this research
is on changes in river channel morphology and bottomland sedimentation
patterns in the upper Little Tennessee and French Broad River systems.
Figure 4.
Little Tennessee River cutbank showing historic and prehistoric strata,
and the position of a radiocarbon date of 770 BC. Long-term average
sedimentation rates in the prehistoric strata are about 0.5 mm/y versus
5.0 mm/y in the historic strata.
The upper Little Tennessee and French Broad River systems, with their wide
alluvial valleys, underwent pronounced changes beginning in the late
1700s. The changes steadily increased through the mid to late 1800s as
widespread agricultural and timber-harvesting activities accelerated
erosion and sedimentation across the region (Ayres and Ashe 1905, Glenn
1911). Subsequent changes in land use played an equally important role in
the ongoing and complex sequence of fluvial landscape response and
recovery. Preliminary observations and a radiocarbon date from an exposed
stream bank (Figure 4) indicate prehistoric sedimentation rates of 0.5
mm/y, and 5.0 mm/y since 1800. Preliminary calculations suggest major
morphological changes in floodplains following European settlement. We
anticipate these changes can be linked to flood frequency, and ecological
interaction between the channel and its floodplain.
We will address the following questions:
1. What is the chronology, frequency, and magnitude of floods and their
interactions with vegetation and land use?
2. What is the rate of sediment accumulation and related changes in
channel morphology?
3. What are the impact signatures of distinct disturbance regimes?
Investigators
Paul Bolstad, University of Minnesota, Forest Processes
Fred Benfield,
Virginia Polytechnic Institute & State University,
Stream Processes
Ted Gragson, University of
Georgia, Human Disturbance Processes
David S. Leigh, University of Georgia, Geomorphic Process
Mark Riedel, USDA-USFS, Hydrology
Bruce Wallace, Universtiy of Georgia, Stream Processes
David Wear, USDA-USFS, Forest Economic Modeling
Jack Webster,
Virginia Polytechnic Institute & State University,
Stream Processes