Graeme Lockaby

Impacts of urbanization on carbon balance in terrestrial ecosystems of the Southern United States

Using a process-based Dynamic Land Ecosystem Model, we assessed carbon dynamics of urbanized/developed lands in the Southern United States during 1945-2007. The results indicated that approximately 1.72 (1.69-1.77) Pg (1P = 10(15)) carbon was stored in urban/developed lands, comparable to the storage of shrubland or cropland in the region. Urbanization resulted in a release of 0.21 Pg carbon to the atmosphere during 1945-2007. Pre-urbanization vegetation type and time since land conversion were two primary factors determining the extent of urbanization impacts on carbon dynamics. After a rapid decline of carbon storage during land conversion, an urban ecosystem gradually accumulates carbon and may compensate for the initial carbon loss in 70-100 years. The carbon sequestration rate of urban ecosystem diminishes with time, nearly disappearing in two centuries after land conversion. This study implied that it is important to take urbanization effect into account for assessing regional carbon balance.

Effects of Forest Regrowth and Urbanization on Ecosystem Carbon Storage in a Rural-Urban Gradient in the Southeastern United States

Forest regrowth after cropland abandonment and urban sprawl are two counteracting processes that have influenced carbon (C) sequestration in the southeastern United States in recent decades. In this study, we examined patterns of land-use/land-cover change and their effect on ecosystem C storage in three west Georgia counties (Muscogee, Harris, and Meriwether) that form a rural–urban gradient. Using time series Landsat imagery data including MSS for 1974, TM for 1983 and 1991, and ETM for 2002, we estimate that from 1974 to 2002, urban land use in the area has increased more than 380% (that is, 184 km2). Most newly urbanized land (63%) has been converted from forestland. Conversely, cropland and pasture area has decreased by over 59% (that is, 380 km2). Most of the cropland area was converted to forest. As a result, the net change in forest area was small over the past 29 years. Based on Landsat imagery and agricultural census records, we reconstructed an annual gridded data set of land-cover change for the three counties for the period 1850 to 2002. These data sets were then used as input to the Terrestrial Ecosystem Model (TEM) to simulate land-use effects on C fluxes and storage for the study area. Simulated results suggest that C uptake by forest regrowth (approximately 23.0 g C m−2 y−1) was slightly greater than the amount of C released due to deforestation (approximately 18.4 g C m−2 y−1), thus making the three counties a weak C sink. However, the relative importance of different deforestation processes in this area changed significantly through time. Although agricultural deforestation was generally the most important C-release process, the amount of C release attributable to urbanization has increased over time. Since 1990, urbanization has accounted for 29% of total C loss from the study area. We conclude that balancing urban development and forest protection is critically important for C management and policy making in the southeastern United States.

Sedimentation associated with forest road surfacing in a bottomland hardwood ecosystem

Abstract Access systems are a necessary element of resource production in bottomland hardwood sites. However, road building may have a detrimental effect on hydrologic function of the site. This report describes initial results of a study designed to examine the effect of different road surfacing treatments on water quality. Four surfacing treatments installed on two test roads included native soil, native soil with vegetative stabilization, 6 cm of gravel, and 15 cm of gravel over geotextile. During the first flooding season periodic sampling measured floodwater suspended sediments and location of erosion and sediment deposition within the road prism. Initial results suggest that sediment movement was confined to the road right-of-way, with no statistically significant sedimentation effects detected beyond the clearing limits of the road. The study is continuing for another field season.

Climatic, ecological, and socioeconomic factors associated with West Nile virus incidence in Atlanta, Georgia, U.S.A.

ABSTRACT: The integrated effects of the many risk factors associated with West Nile virus (WNV) incidence are complex and not well understood. We studied an array of risk factors in and around Atlanta, GA, that have been shown to be linked with WNV in other locations. This array was comprehensive and included climate and meteorological metrics, vegetation characteristics, land use / land cover analyses, and socioeconomic factors. Data on mosquito abundance and WNV mosquito infection rates were obtained for 58 sites and covered 2009–2011, a period following the combined storm water - sewer overflow remediation in that city. Risk factors were compared to mosquito abundance and the WNV vector index (VI) using regression analyses individually and in combination. Lagged climate variables, including soil moisture and temperature, were significantly correlated (positively) with vector index as were forest patch size and percent pine composition of patches (both negatively). Socioeconomic factors that were most highly correlated (positively) with the VI included the proportion of low income households and homes built before 1960 and housing density. The model selected through stepwise regression that related risk factors to the VI included (in the order of decreasing influence) proportion of houses built before 1960, percent of pine in patches, and proportion of low income households.

Monitoring Land-Use and Land-Cover Change in the Eastern Gulf Coastal Plain 3 using Multi- temporal Landsat imagery

Rapid population growth and intensifying human activities have driven significant changes in coastal plains. As one of the largest coastal plains in the world, the U.S. Gulf Coastal Plain supports a huge population and provides numerous goods and ecological services to the human society. Spatial information on Land-Use and Land-Cover Change (LULCC) is essential for accurate assessment of human impacts on the structure and functioning of coastal ecosystems in this region. In this study, the Florida Panhandle region was selected as a case to characterize and detect changes in Land Use/Land Cover (LULC) in the Gulf Coastal Plain from 1985 to 2005. Landsat TM images in 1985, 1996 and 2005 were collected and processed to retrieve LULC information and to reflect temporal changes of major LULC types. Results indicated that urban areas expanded quickly and increased by about 79% from 1985 to 2005. Crop/pasture decreased from 1985 to 1996 but increased quickly during 1996-2005 by replacing large area of forestland in the eastern part of the study area. Forest/woody wetland increased from 1985 to 1996 but decreased in the later time period. Population growth and tree plantation were identified as the two major driving forces for LULCC in this area. Our results imply that urban sprawl and cropland/pasture expansion as well as tree plantation could potentially affect productivity, carbon and nutrient cycling, as well as water quality in coastal ecosystems of the Gulf of Mexico. Uncertainties associated with satellite image classification and scale effect should be further addressed in future research.

Influence of Microclimate on Short-Term Litter Decomposition in Loblolly Pine Ecosystems

Recently, there has been much concern expressed over projected increases in global temperatures (Schneider, 1989), and the subsequent effects on terrestrial ecosystems (Woodward, 1992). Atmospheric levels of carbon dioxide and other trace greenhouse gases such as methane and chlorofluorocarbons are increasing at a dramatic rate (Mooney et al., 1987; Schneider, 1994). Increases in these gases and potential trapping of infrared radiation have led to predictions by general circulation climate models (GCMs) of global surface temperature increases from 1.5 to 4.5 °C over the next 50 to 100 years (Hansen et al., 1981; Bretherton et al., 1990). These models have also predicted shifts in the global water cycle, although the magnitude and direction of change is less certain.