Paleoenvironmental Range of Variation in Floods, Fires, and Biomes in the Upper Little Tennessee River Valley, Blue Ridge Mountains
Overbank alluvium from rivers and streams in the Upper Little Tennessee River valley provides a multi-millennial record of the range of variation in flooding conditions, bottomland sedimentation rates, fires (charcoal records), and biome changes that allow a long-term view of the regional range of variation of those natural systems. Several stratigraphic sections have been collected from vertical accretion floodplain sediments that allow paleoenvironmental insights over the past 2000 years. Sand sedimentology indicates intense flooding conditions around the beginning and end of the Medieval Climate Anomaly (ca. 800-1300 cal yr BP). Historical floodplain sedimentation rates are about and order of magnitude more than any prehistoric conditions, and there is no indication that prehistoric Mississippian and Cherokee agricultural activities accelerated erosion and sedimentation. A continuous 11,500 year sedimentation record was recovered from a meander scar in the Upper Little Tennessee River valley near Otto, North Carolina. Analysis of charcoal and stable carbon isotopes from this stratigraphic section provides insights about past fire frequency and major shifts in biome composition with respect to C3 versus C4 plants in the watershed. The carbon isotopes indicate shifts in C3/C4 composition corresponding with the 8.2 ka climate change event, and during the late Holocene the charcoal and isotopic data are consistent with the idea that Native Americans used fire to manage forests and to expand agricultural activities that involved C4 plants (i.e. maize) during Woodland and later times. In summary, the paleoenvironmental record provides uniquely important background for framing and evaluating modern conditions in the region.
Dept of Geography, University of Georgia, Athens, GA
86 • Peter A. Wilfahrt1, Julie P. Tuttle2, Peter S. White3
Assessing the Disparities and Similarities in Functional Diversity of Tree Communities Following Natural and Anthropogenic Disturbance
Natural disturbances act to reset affected patches of forest to earlier successional stages, creating a patchwork of forest ages and types across the landscape. Tree species often exhibit a trade-off between being able to rapidly colonize disturbed spaces or achieve competitive dominance over other species in the long term. Such trade-offs may be further defined in terms of the nature of the disturbance and how species withstand or respond to it. These trade-offs can be measured in the form of functional traits such as seed mass and wood density, and the trait space describing tree communities should vary predictably in response to disturbance. As the predominant forms of disturbance shift increasingly toward being caused by anthropogenic forces such as logging, a question emerges as to whether post-harvest forests occupy similar trait space as those created from natural forms of disturbance such as wind throws, fire events, and ice storms. This talk uses the USDA’s Forest Inventory and Analysis database along with trait data for tree species to examine this question for central hardwood forests. It examines how the trait spaces of tree seedlings, saplings, and adult trees vary with respect to different types of disturbance, and whether there is a convergence toward trait-space similarity between natural and anthropogenic disturbance.
1 Dept of Biology, University of North Carolina, Chapel Hill, NC; 2 Curriculum for the Environment and Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC; 3 Dept of Biology and Curriculum for the Environment and Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC
When Great Smoky Mountains National Park (GRSM) was placed under strict protection in 1934, about 20% of the landscape was old-growth forest that had never been logged or farmed, and about 80% was second growth recovering from logging and settlement. Through the work of Whittaker (1956), the park’s old-growth vegetation became an enduring textbook example of vegetation and species distributions, and we might expect that the structure of GRSM’s old-growth forests today would capture the natural range of variation of these southern Appalachian forests, subject only to localized natural disturbances such as landslides, flooding, windthrow, ice storms, and fire. Despite protection, however, multiple indirect, diffuse anthropogenic disturbances--including exotic pests, fire suppression, atmospheric deposition, and changes in herbivory--have continued to impact both old-growth and successional GRSM forests. Here, we employ a mid-1930s vegetation survey and a compilation of more recent vegetation data sets (1970s-2000s) to compare the historic and present-day range of variation in GRSM forest structure and composition. First, we illustrate changes in disturbance by mapping the distribution of known natural and anthropogenic disturbances before and after park protection. We then compare GRSM forests of the 1930s and 1970s-2000s in both old-growth and second-growth areas, focusing on 1) the range of variation in basal area and density and 2) dominance and distribution of disturbance indicator species (i.e., based on shade tolerance and fire sensitivity). We highlight changes in these metrics for particular vegetation/site types and discuss the impact of ongoing, diffuse anthropogenic disturbance on GRSM forest structure.
1 Curriculum for the Environment and Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC; 2 Dept of Biology and Curriculum for the Environment and Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC
88 • Kendrick Weeks1, Cathryn H. Greenberg2, Susan C. Loeb3, Gordon S. Warbuton4
