Lots of Weeds: Insular Phytogeography of Vacant Urban Lots

Abstract

The flowering plant species richness of twenty-six vacant urban lots which varied in age, size, isolation from other lots, and in intensity of 'weed control' (sporadic seasonal mowing), was investigated in the light of equilibrium island biogeographic theory. Species richness for all lots increased logarith- mically with lot age. The species richness of lots 40 months and older, each of which had been mown at least once, did not increase with age, and was posi- tively related to lot area and negatively related to measures of lot isolation. These results suggest that species richness had reached or was nearing equilibrium in these older-mown lots, possibly due to mowing and immigration-extinction phenomena, and that other lots are significant sources of colonists. That the slope of a plot of log-species richness against log-area for the older-mown lots is similar to that for oceanic islands suggests that these lots have immigration- extinction rates similar to those of true islands.