Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2008
Publication Date: 1/1/2009
Citation: George, K., Ziska, L.H., Bunce, J.A., Quebedeaux, B., Hom, J.L., Wolf, J., Teasdale, J.R. 2009. Macroclimate Associated with Urbanization Increases the Rate of Secondary Succession from Fallow Soil. Oecologia. 159:637-647. Interpretive Summary: The aim of the study was to see if plant succession was altered by changes in atmospheric carbon dioxide and air temperature. In the field of plant ecology, succession is the gradual and orderly process of ecosystem development brought about by changes in plant species composition. Plant succession is initiated after a disturbance that removes much of the existing vegetation. In this study we examined the changes in community composition following the abandonment of agriculture. The study took place at three locations: Baltimore city center (Urban), a nature center on the outskirts of Baltimore (Suburban) and an organic farm 50 km from Baltimore (Rural), which represent a decrease in urbanization. Monitoring of the atmosphere at these three sites revealed that over several years, atmospheric carbon dioxide and air temperature was highest at the urban site and decreased as urbanization was reduced. The elevated levels of carbon dioxide and temperature in the urban area are consistent with atmospheric changes predicted to occur in the future from global climate change. On average over the five years of the study aboveground plant biomass was highest at the urban site compared to the suburban and rural sites. The ratio of longer-lived (perennial) plant species to short-lived (annual) plant species was also higher at the urban site after five years indicating the development of the ecosystem was proceeding at a faster rate. The increased mass of plants and change in species present at the urban site correlated with increased carbon dioxide concentration and air temperature. The study indicates that plant succession on an agricultural soil may be increased with global climate change. This study will provide important information for farmers managing fallow agricultural systems and weed control. It will also be of interest to plant ecologists and ecophysiologists studying the effects of climate change on plant communities.
Technical Abstract: We examined the effect of elevated atmospheric CO2 and air temperature from urbanization on the initiation and progression of secondary succession following the abandonment of agricultural practices. A gradient of atmospheric CO2 and air temperature along a rural-urban transect was used to investigate changes in agricultural plant communities over five years. Replicate plots of fallow agricultural soil were established in the following three locations: Baltimore city center (Urban), a nature center on the outskirts of Baltimore (Suburban), and an organic farm 50 km from Baltimore (Rural). Over the five years the urban site on average was 2.1 degrees warmer and had an atmospheric CO2 concentration elevated by 16% compared to the rural site. Other environmental variables measured across the transect, including ozone, did not differ consistently. The first year of plant growth from a fallow soil was dominated by annual species with greatest aboveground biomass at the urban site, lowest biomass at the rural site, and intermediate biomass at the suburban site. The large quantity of litter produced from annual biomass at the urban site suppressed annual seed emergence, facilitating the establishment of perennial plants. After five years the plant communities at each site were significantly different from each other, with the urban site biomass dominated by woody perennials (the majority of this biomass from two invasive species) and the suburban and rural sites still dominated by annual species, although dominance was decreasing over time. The increase in the ratio of perennial to annual species and rapid accumulation of biomass at the urban site suggest a faster rate of secondary succession was associated with elevated atmospheric CO2 concentration and air temperature. Global changes in atmospheric CO2 concentration and air temperature may accelerate secondary succession upon abandonment of agricultural land. This could increase the productivity and stability of communities across the landscape.