Canopy gap dynamics in old-growth riparian forests along low order streams, Adirondack Mountains, New York

Recent research has suggested that canopy gap dynamics in temperate, late-successional riparian forests may influence organic matter recruitment and the light environment over streams. However, controls on gap dynamics specific to riparian forests are poorly understood in the northern forest region of eastern North America. We hypothesized that gaps would be larger and more frequent closer to streams. We also expected large gaps to be the product of multiple wind disturbances causing gap expansion over time. The 4 study sites lie in old growth hemlock-northern hardwood forest along low order streams in Adirondack Park, NY. All gaps within the four 6-9 ha plots were mapped and characterized based on the number of gapmakers, expanded gap area, slope, and aspect. We recorded the species, decay stage, orientation, DBH, and type of damage (snap, uproot, snag) for each gapmaker. Increment cores were extracted from gapmakers and perimeter trees at 25% of gaps. Relationships between topography and gap characteristics were examined using spatial statistics, ANOVA, and multiple regression. The total area in expanded gaps ranged from 19-48%. Gaps in all sites had random spatial distributions. Spatial autocorrelation occurred in the distribution of canopy gap size in 2 sites (p=0.01, 0.002). Slope, aspect, and distance from stream did not significantly predict gap size, but the percent forest canopy in gap did vary with stream distance in two sites. Our results suggest an interaction between low order riparian landforms and gap distribution in late-successional forests, resulting in a complex pattern of canopy openings along stream reaches.