Can Understory Plant Composition and Richness Help Designate Riparian Management Zones in Mesic Headwater Forests of the Northeastern United States?

Riparian buffers implemented to minimize sediment, nutrients, and disturbance impacts on streams during forest operations vary greatly in the degree to which ecological criteria are used in their design. Because most forest operations are concentrated around headwater streams, our primary research objective was to identify a floristically based riparian boundary for headwater streams using plant species composition and indicator species to classify riparian environments distinct from the surrounding upland forest. Within three forested regions of the Northeast US, understory vegetation plots were sampled along perpendicular transects extending from the stream bank into the upland forest. At all sites, species richness was highest adjacent to the stream, decreasing exponentially within 6-12 m from the channel. Species composition closest to the stream was significantly different from all other lateral distances, but identified riparian indicator species were of limited practical use across all sites. However, changes in species richness can serve to identify a riparian area extent up to 6-12 m from headwater streams. Study Implications: Riparian areas around headwater streams can be sensitive to forest management activities, particularly harvesting. Riparian management zone (RMZ) buffers around these streams vary in the degree to which they are based on ecological criteria; for example, fixed-width buffers may or may not adequately protect the riparian area. Our study within three forests of the Northeast detected a significant exponential decreasing trend in understory plant species richness within 6-12 m (20-40 ft) from the stream bank. We believe this ecologically based floristic zone closest to the stream represents the most sensitive part of the RMZ.This study recommends a 12 m (40 ft) zone to maintain the majority of the forest cover and minimize the impact of logging equipment. Foresters should be cognizant of this 12 m zone when implementing silvicultural activities and planning harvest access systems.

Automated summary

This study identified a floristically based riparian boundary for headwater streams, with the most species richness closest to the stream gradually decreasing within 6-12 meters. Riparian indicator species were found to have limited practical use. The study recommends a 12-meter zone to maintain forest cover and minimize the impact of logging equipment in riparian areas.