Woody plant colonization in an experimentally fragmented landscape



The pattern of distribution and abundance of woody plants colonizing old fields is influenced by landscape spatial features, in particular, by the distance from the old field to propagule sources and the size of the habitat patches undergoing succession. Colonization is also influenced by species life history traits, such as dispersal mode, growth form, and fecundity. As part of a long-term project studying effects of habitat fragmentation on secondary succession at the prairie-forest ecotone, we have examined the colonization patterns of early-successional woody plants in an experimentally fragmented old field, with emphasis on the three woody species [Cornus drummondii C. A. Mey (rough-leaved dogwood), Ulmus rubra Muhl. (slippery elm), and 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. The rate of colonization by C. drummondii showed a pattern of acceleration after its initial colonization, consistent with rapid in situ recruitment from 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. rubra, density is currently greater in large patches than in small patches. No patch size difference was found for J. virginiana. The stern density of both C. drummondii 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 patches. Our results highlight the importance of life history traits of colonizing species and spatial aspects of habitat during succession.