Riparian woody plant traits across an urban–rural land use gradient and implications for watershed function with urbanization

Worldwide riparian forests are increasingly threatened by urbanization and land use change. Plant trait-based analyses provide a useful approach for comparing and describing distinct plant communities and may offer a more general understanding of the influences and consequences of disturbance associated with land use on riparian vegetation. This research addressed two primary questions focusing on nine plant traits that may significantly influence ecological processes or function. Are riparian woody plant traits related to the surrounding watershed matrix? Are trends in plant traits that are related to the watershed matrix also evident in the riparian woody plant regeneration layer? Using a rapidly urbanizing region of the southeastern United States near Columbus, GA as an example, data on woody plant species composition were collected from 17 forested watersheds along headwater streams representing an urban-to-rural land use gradient. Land cover and hydrologic indices were used to characterize the watershed landscape matrix at each site. Plant species were described by morphological, physiological, and reproductive trait groups. A site × trait matrix was obtained and detrended correspondence analysis (DCA) ordinations were used to identify trends in plant traits. Correlative analyses were used to relate watershed matrix indices to plant traits. Analyses indicated that riparian woody plant traits were related to the surrounding watershed matrix, most notably flood intolerance showed increased importance in urban areas possibly signifying a shift in hydrologic function. Changes in riparian woody plant traits are related to the watershed matrix and may have significant implications for ecological function and structure as urbanization continues.