An analysis of historical wetland loss in an urban landscape

Background/Question/Methods By 2030, 60% of the world's human population will live in urban areas, causing a great deal of alteration to the remaining natural habitat. The Orlando metropolitan region is an excellent case to study the effects of urbanization, as the conversion from natural or agricultural lands to urban habitat is relatively recent (within the last 50 years) and remains ongoing. Cypress domes (isolated wetlands dominated by bald cypress, Taxodium distichum) offer an excellent system to study ecological effects of urbanization because they are discrete habitats that are readily distinguishable on color infrared (CIR) aerial photography and can remain relatively intact in urbanized areas. Cypress domes can be affected by urbanization through fragmentation and loss of habitat that eliminate and isolate domes and through alterations to hydrology and fire regime that degrade the habitat. We evaluated change in number, spatial pattern, and sizes of cypress domes between 1984 and 2004 in the Orlando region for five levels of urbanization (natural, agricultural, low urban, medium urban, and high urban). We hypothesized that urbanization would cause a decrease in the number and an increase in spatial isolation of cypress domes.

Results/Conclusions We found that one half of cypress domes present in natural lands in 1984 were lost by 2004, primarily from degradation of the habitat, causing the bald cypress to no longer be visible on CIR photography. The number of low urban domes tripled during the 20 year period, especially at the fringe of the city, due mainly to conversion from natural areas. Using Ripley's K and a spatial isolation index, we found that urban domes showed a decrease in spatial isolation (increased clustering) due to conversion of contiguous tracts of the land, and consequent reclassification of domes, from natural to low urban. Wetland sizes have become more homogenous because large urban domes and small agricultural and natural domes were lost. We infer that metapopulation-level processes (e.g. dispersal, gene flow) now occur among more degraded habitat and in a less suitable urban matrix. This study helps demonstrate that urbanization can cause rapid changes in “protected” habitat with potentially important long-term consequences on the ecology of these systems.