CUERE Seminar: Dr. John Lagrosa

Urban watersheds are heterogeneous, complex mosaics of developed and vegetated areas with variable structure and dynamics. Urban areas develop via significant land-use and land cover (LULC) change. LULC change is a primary driver of terrestrial carbon release, often through the conversion of forested areas into agriculture or the expansion of urban areas from population growth. Current understanding of the effect of LULC change on carbon storage is limited for subtropical urban watersheds. This study investigates the effect of LULC change on above-ground tree carbon (AGTC) in a sub-basin of the Tampa Bay Watershed, Florida. An existing LULC classification was modified to incorporate differences in AGTC. LULC change was then modeled using the Dyna-CLUE framework for a five-year period. Finally, LULC change was integrated with AGTC to project future quantities under three landscape scenarios: baseline, increased and aggressive rates of development. The reclassification showed significant differences in AGTC between residential and other urban classes, which are sometimes aggregated into a single class. Observed LULC data from 1995–2011 showed a decrease in land area for agriculture, rangeland and upland forests by 49%, 56% and 27% respectively. This coincided with a 22% increase in residential and 8% increase in built areas, primarily between 1995 and 2004. Modeled LULC change showed a continued reduction in agriculture and rangeland, along with the expansion of residential and infrastructure classes. A 12% increase in total landscape AGTC occurred from 2006-2011 as agriculture and rangeland were converted to residential, infrastructure and built classes. Scenario projections for 2016 show an additional increase of 11% AGTC under baseline change, 15% under increased development and 18% under aggressive development. These results suggest that residential expansion may cause an increase in AGTC storage as agriculture and rangeland areas are replaced. However, as agriculture and rangeland disappear, LULC change patterns could shift, with residential expansion replacing upland and wetland forested areas causing a long-term decrease in AGTC. This information can help decision-makers identify areas as potential carbon sources or sinks. Further, the methodology is presented to establish a framework that can be parameterized and adapted for analyses in other urban areas.