Riparian areas are three-dimensional ecotones that provide numerous environmental services and benefits, from ensuring good water quality to providing critical habitat for wildlife and aquatic organisms. Riparian buffers designated by forest managers to protect these areas can be of fixed or variable-width. In practice, buffer widths are not typically based on ecological criteria, as there is no consensus on what ecosystem attributes should be used to define the buffers. Contrary to dryland regions, the mesic mixed forests of northeastern North America do not show obvious zonation in vegetation types or species, except along high-order streams. However, riparian areas are extremely sensitive to logging and other human activities; thus, a need exists to delineate management buffer widths based on ecologically sound criteria.
Our primary research objective was to identify an ecologically based riparian boundary for first- and second-order streams using plant species composition and indicator species to signify riparian environments distinct from the surrounding upland forest. Within four sampling locations distributed between three distinct regions of the Northeast U.S., we sampled understory vegetation plots at regular distances along transects extending from the stream bank into the upland forest.
Results/Conclusions
We observed significant differences in species composition between the four sampling sites. At all sites, species richness was highest adjacent to the stream, decreasing exponentially within 12 m from the stream. Species composition closest to the stream was significantly different from all other lateral distances at two research sites. Though riparian indicator species occurred at each site, no region-wide indicator species was identified to delineate a commonly defined riparian area across the Northeast. However, changes in species richness and community composition can serve to identify the riparian area up to 12 m from headwater streams. Because headwater streams are disproportionately affected by forest management activities, and riparian protection guidelines are rarely based on locally available data, evidence-based studies such as the current research should guide regional riparian management to ensure that these areas continue to provide ecosystem services now and into the future.