Natural Plant Establishment along an Urban Stream, Onondaga Creek, New York

摘要

Urbanization results in a suite of harmful effects to streams, including removal or degradation of riparian vegetation. Many stream-restoration programs address this by adding plants, with limited quantitative knowledge about vegetation dynamics already occurring within the stream corridor. This project examined natural plant establishment along an urbanized stream channel in Syracuse, NY. It had three objectives: first, to relate plant establishment along an urban stream gradient to substrate condition; second, to quantify seeds dormant in the soil at those same sites; and third, to indicate what passive revegetation responses might occur to various treatments along a rural-to-urban gradient. Three sites were selected along such a gradient on Onondaga Creek, near Syracuse, NY. Vegetation plots were established at each site to assess plant germination and establishment under substrate conditions designed to mimic restoration interventions. We also conducted a seedbank study using soil cores collected from these sites. Plant communities were dominated by grasses and forbs. Numbers of alien species increased from 34% at more rural sites to 51% at more urban sites. Seedlings of native riparian trees nonetheless germinated at all three sites along thegradient. Recruitment of native riparian trees (especially Populus deltoides [Eastern Cottonwood], Fraxinus pennsylvanica [Green Ash], and Acer negundo [Boxelder]) exceeded non-native and invasive ones. The riparian seedbank showed disproportionate dominance by herbaceous plants (95.5% of individuals) at all locations surveyed, and invasive species were common (about 25% of all germinants). This study shows some potential for natural regeneration of native trees, but also found a significant source ofinvasive plants in the soil seedbank that could reduce restoration success. Notably, the study recorded the presence of 16 bryophyte taxa, and the common ones were those typically associated with disturbances.