The distribution of plant species in urban vegetation fragments

Abstract

(1) The presence and absence of 22 plant species of various growth forms and habitat associations were analysed in 423 habitat fragments totalling 10.4 km2 in a 268 km2 urban and suburban region, in Birmingham, UK. (2) Multivariate logistic regressions were used to assess the effects of patch geometry and quality on the species distributions. Measures of geometry were area, shape (S-factor), distance from open countryside and various measures of isolation from other patches. Potential habitat for each species was determined quantitatively, and the distribution of each species was considered within a subset of patches containing potentially suitable habitat types. There was found to be a significant positive correlation between the density of patches available to a species and the proportion of these patches which were occupied. (3) Logistic analyses and incidence functions revealed that, for many of the species, occupancy increased with site age, area, habitat number and similarity of adjacent habitats, while increasing distance to the nearest recorded population of the same species decreased the likelihood that a species would be found in a patch. (4) Patterns of occupancy are consistent with increased extinction from small sites, and colonisation of nearby habitats, coupled with an important role for site history. We conclude that spatial dynamics at the scale of the landscape are of importance to the long-term persistence of many plant species in fragmented landscapes, and must be seriously considered in conservation planning and management. These results have direct implications for the siting and connectivity of urban habitat reserves.