Spatial characteristics of canopy disturbances in riparian old-growth hemlock - northern hardwood forests, Adirondack Mountains, New York, USA

Gap dynamics in temperate, late-successional forests influence important riparian functions, including organic matter recruitment and light environments over streams. However, controls on gap dynamics specific to riparian forests are poorly understood. We hypothesized that (i) gaps are larger and more frequent nearer streams, (ii) gaps cluster at withinstand scales, and (iii) tree damage type and gap fraction vary among riparian landforms. All gaps within four 6-9 ha plots in riparian old-growth eastern hemlock (Tsuga canadensis (L.) Carriére) - northern hardwood forest in the Adirondack Mountains, New York, USA, were mapped and measured. We recorded species, damage type, and diameter at breast height for gapmakers and dominant perimeter trees. Spatial distribution was assessed with Ripley's K. Spatial autocorrelation in gap area and tree damage type were assessed using Moran's I. Linear regression analysis defined relationships between proximity to streams and gap area and frequency. Expanded gap fraction ranged from 28.3% to 47.6%. Gaps were randomly distributed at scales ≤25 m and clustered at scales of 63-122 m. Distribution patterns were not consistent at other scales. Convergent and divergent landforms significantly influenced gap fraction, tree damage type, and species distributions. Positive correlations between convergent topography and gap area suggest an interaction between low-order riparian landforms and gap formation dynamics in late-successional forests.