Ozone Trends in Great Smoky Mountains National Park Over the Past Two Decades: Evidence That the Clean Air Act Works
Ozone data from five sampling locations in Great Smoky Mountains National Park and one location outside the Park in NC were analyzed over the period 1989 to 2012 for diurnal and season trends. Sampling locations spanned an elevational range from 564 m at Cades Cove to 2030 m at Clingmans Dome in TN. Ozone concentrations [O3] show an early morning minimum around 6 am at low elevations and a peak between 1 and 4 pm. High elevation sites have flatter profiles with minimum [O3] occurring between 8 and 11 am, while maxima often occur at night. Purchase Knob in NC has lower maxima than a site at the same elevation in TN. This most likely reflects scavenging, as winds move primarily west to east, and also dilution by mixing with air in the free troposphere as it moves over the Park. Seasonal exposures increased from 1989 to 1999 and then dropped after 2003. The frequency of hours with [O3] > 60 ppb has decreased substantially since 2003, especially at high elevation sites. This has been attributed to the implementation of the 1997 8-hour O3 standard (NOx SIP call) as required by the Clean Air Act, a slow-down in the economy, and turnover in the motor fleet to less polluting vehicles. These reductions show that the Clean Air Act has had highly beneficial consequences. People and natural ecosystems in the Park today are at much lower risk from tropospheric O3 than they were a decade ago.
Dept of Biology, Appalachian State University, Boone, NC
174 • Matthew S. Herron, Joydeep Bhattacharjee
Evaluating Multiple Restoration Strategies in a 30 Year Old Bottomland Hardwood Forest Restoration Site
In the Lower Mississippi Alluvial Valley (LMAV) hydrologic modification and clearing for agriculture have led to over 75% loss of the original 10 million hectares of bottomland hardwood forest (BHF). Efforts to reforest former agricultural land have involved planting of heavy-seeded species, under the assumption that understory vegetation would return naturally. This has resulted in largely monotypic stands of oak species with closed canopies that inhibit the growth and regeneration of a more diverse mid- and understory. Select areas, however, were left fallow for research purposes and provide an important glimpse into how regeneration may have naturally occurred. Previous studies on community assembly in restored BHFs have examined either planted areas, silvicultural manipulations or passive fallow areas, but none have compared all three or taken into account landscape level factors such as edge effect, distance to nearest stream or land surface roughness. In this study, we are evaluating the effects of 3 silvicultural treatments on historic oak plantings at the Ouachita Wildlife Management Area near Monroe, LA to see how they influence understory plant diversity. We are also assessing the successional trajectories of 9 fallow and 9 planted research plots spread throughout the 5500 hectare site, to determine patterns and mechanisms of old-field assembly. We compare these different management strategies (silvicultural treatments and planted and fallow controls) in light of landscape level factors to gain a better understanding of BHF ecology and restoration. Our primary goal is to identify economically viable, ecologically sound prescriptions to aid in the future management and restoration of bottomlands across the state and the LMAV.
Comparison of Diurnal Water Use in the Native Riparian Tree Species, American Sycamore, Platanus occidentalis (L.), and Black Willow, Salix nigra (Marshall), and the Potential Implications for Riparian Restoration Efforts and Ecology
Riparian forests provide numerous environmental services such as contributing to stream bank integrity, providing nesting sites, and helping to stabilize micro habitats in and around bodies of water. Therefore restoration of these forests is an important part of protecting and maintaining healthy watersheds. We compared water use in co-occurring American sycamore and black willow growing along a stream on the Kennesaw State University campus, located in north west Georgia. For the comparison we used Granier style heat dissipation probes and an onsite weather station. Initial findings indicate the two species differ in relative amounts of water use as well as in the degree of correlation between their water use and vapor pressure deficit (VPD). Black willow appears to use significantly more water per unit of stem cross sectional area compared American sycamore. Water use in black willow also presents a stronger correlation to VPD than American sycamore. Initial findings suggest black willow may transpire at night with its transpiration potentially driven by fluctuations in VPD. These differences in water use and environmental response along with differences in species life history may have implications for riparian restoration projects and add to the understanding of riparian forest ecology.
Dept. of Biology & Physics, Kennesaw State University, Kennesaw, GA
176 • Scott A. Abla, Laura E. DeWald
Multi-Severity Fire Effects in Xeric Oak-Pine Communities Following Small Fires in the Great Smoky Mountains National Park
Fire suppression has changed species composition in the southern Appalachians. Improved understanding of fire-related ecological mechanisms will improve effectiveness of fire management decisions. Although occurrence of fire is known to be related to ecosystem functioning, specific effects of multi-severity fires are not as well understood. The purpose of this study was to evaluate ecosystem effects of different fire severities in xeric oak-pine ecosystems in the Great Smoky Mountains National Park (GSMNP). Plots were randomly located using satellite-based burn severity maps, and ground-truthed using the FIREMON Composite Burn Index. Variables related to stand regeneration were measured at the ground, midstory, and overstory layers among different burn severities including no-burn sites. Results showed overstory mortality increased with higher burn severity and fire at all severities reduced litter layer and shrub cover by over 50% while grass cover and coarse woody debris increased. Species richness did not differ among severities in ground and midstory layers. However, desired xeric pine and oak regeneration was greater at higher fire severity. Maple was the dominant species in the ground and midstory layers (seedlings in unburned sites, sprouts in burned sites), but mid- and overstory basal area decreased significantly with fire severity. Changes in species composition following fire were caused by greater amount of exposed mineral soil, increased light penetration to forest floor, and reduced midstory stem densities. These results show that fire can be used to create conditions that promote xeric oak-pine regeneration and thus help protect this ecosystem in the southern Appalachians.
Biology Dept, Western Carolina University, Cullowhee, NC
