Woody plant colonization in an experimentally fragmented landscape

The pattern of distribution and abundance of woody plants colonizing old fi elds is influenced by landscape spatial features, in particular, by the dis tance from the old field to propagule sources and the size of the habitat p atches undergoing succession. Colonization is also influenced by species li fe history traits, such as dispersal mode, growth form, and fecundity. As p arr of a long-term project studying effects of habitat fragmentation on sec ondary succession at the prairie-forest ecotone, we have examined the colon ization patterns of early-successional woody plants in an experimentally fr agmented old field, with emphasis on the three woody species [Cornus drummo ndii C. A. Mey (rough-leaved dogwood), Ulmus rubra Muhl. (slippery elm), an d Juniperus virginiana L. (red cedar)], which currently dominate the woody community on the site. The shapes of the colonization curve (proportion of colonized quadrats vs time) differed between C. drummondii and U. rubra. Th r rate of colonization by C. drummondii showed a pattern of acceleration af ter its initial colonization, consistent with rapid in situ recruitment fro m clonal growth and early seed production. By contrast, colonization by U. rubra fits a roughly linear pattern, consistent with recruitment only from external propagule sources. For both C. drummondii and U. rubin. density is currently greater in large patches than in small patches. No patch size di fference was found for J. virginiana. The stem density of both C. drummondi i and U. rubra exponentially decreased with distance to external propagule sources. The negative exponential pattern of U. rubra (wind-dispersed) with distance is sharper than that of C. drummondii (bird-dispersed), Moreover. the amount of spatial variation in density explained by distance to source is greater on small parches. Our results highlight the importance of life history traits of colonizing species and spatial aspects of habitat during succession.