This Is AuburnElectronic Theses and Dissertations

Impact of urbanization on biogeochemical cycling in western Florida




Enloe, Heather

Type of Degree



Forestry and Wildlife Sciences


Many city residents may benefit from the ecosystem services that urban forests provide. An important supporting process to ecosystem services is nutrient cycling. Very few studies examining the impacts of urbanization on nutrient cycling and soil carbon storage have taken place in the coastal regions of the southeastern United States, one of the fastest growing regions in the United States. The focus of this study was to investigate the impacts of urbanization on soil biogeochemical cycling in western Florida (panhandle) across six land covers. The land covers in this study include rural slash pine (Pinus ellottii) plantations, rural naturally regenerating forests (slash pine or mixed oak dominated), urban forest fragments (slash pine or mixed oak dominated) and urban lawns. Soil organic carbon content in urban forests has mean values of 24.5 kg cm-2 in the 0 to 90 cm mineral soil and both increases and remains unchanged from that found for rural forests depending on the dominant overstory vegetation type. Urbanization appears to stimulate soil microbial biomass and activity (potential carbon mineralization rates) in the forest sites. Urban forest pine dominated sites are found to have 2.5 times as much N mineralized on a daily basis as natural forest pine sites and urban forest oak sites are found to have 1.9 times as much N mineralized as natural forest oak sites based on the mean daily rates averaged over the two year study. Urban forest sites and urban lawns sites in the study area are not significantly different in their soil carbon and nitrogen contents in the mineral soil (0 to 90 cm), microbial biomass carbon and nitrogen contents, potential carbon mineralization rates, and potential net total N mineralization rates. Potential net nitrification rates in unfertilized lawns in this study are significantly higher than those in urban forests, with nitrification composing the entire potential net N mineralized in urban lawn soils. Urban sites are on average warmer by 0.63 oC (p=0.0101) than rural sites in the winter and tend to have a more narrow temperature range than the rural forested sites. These alterations of the forest floor temperature is not reflected in different mass loss or nutrient release patterns in decomposing litter among contrasted land covers (urban forest oak versus natural forest oak and urban forest pine versus natural forest pine). Foliar mass loss was measured over an 82 week period that was characterized by periods of extended drought, which may have masked an urbanization effect. Oak and pine dominated stands do have distinct differences in biogeochemical cycling. This may suggest that future urbanization studies in this region need to account for the overstory composition of a forest stand, as this may reflect differences in stand origin that then may impact biogeochemical cycling and the overall effect of urbanization.