Spatial and temporal patterns of plant communities near small mountain streams in managed forests

Riparian plant communities along small streams occupy a small proportion of the total landscape but can provide disproportionally large ecological, social, and economic benefits. We examined plant communities at 25 study sites along small fish-bearing streams in temperate managed forests of the Pacific Northwest spatially as a function of distance from stream and temporally by assessing a chronosequence of stand ages: young (31-51 years), mature (52-70 years), and old (> 100 years). We identified three distinct vegetation communities based on species cover and richness in shrub and herb layers: riparian (0-9 m), transitional (10-29 m), and upslope (30-80 m); 12 species were indicators of these vegetation communities. For tree species, basal area increased with stand age. Shrub species cover and richness were greatest in old stands, but herb species richness was highest in young stands. Composition varied with stand age; 15 species were indicators of these differences in composition. These results, together with information on successional and wetland status, suggest that plant communities on small fish-bearing streams reflect geomorphic and fluvial settings but also follow successional patterns found in natural forests. These stands will become some of the primary unharvested, older forests within the managed forest landscape and provide insights for effective riparian management on sites impacted by historical management practices prior to the regulations requiring riparian buffers.