14Understanding the effects of management on forest structure and function is increasingly 15 important in light of projected increases in both natural and anthropogenic disturbance severity 16 and frequency with global environmental change. We examined potential impacts of the 17 procurement of forest-derived bioenergy, a change in land use that has been suggested as a 18 climate change mitigation strategy, on the productivity and structural development of aspen-19 dominated ecosystems. Specifically, we tested the effects of two factors: organic matter removal 20 (stem-only harvest, whole-tree harvest, whole-tree harvest plus forest floor removal) and soil 21 compaction (light, moderate, and heavy) over time. This range of treatments, applied across three 22 sites dominated by aspen (Populus tremuloides Michx.) but with different soil textures, allowed 23 us to characterize how disturbance severity influences ecosystem recovery. 24Disturbance severity significantly affected above-ground biomass production and forest 25 structural development with responses varying among sites. At the Huron National Forest (sandy 26 soils), the removal of harvest residues reduced above-ground biomass production, but no 27 negative effect was observed following whole-tree harvest at the Ottawa and Chippewa National 28 Forests (clayey and loamy soils, respectively) relative to stem-only harvest. The density of stems 29 greater than 5 cm DBH and maximum diameter exhibited negative responses to increased 30 disturbance severity at two sites, indicating that structural development may be slowed. Overall, 31 results suggest that disturbance severity related to procuring harvest residues for bioenergy 32 production may impact future productivity and development, depending on site conditions and 33 quality. 34 35

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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 within-stand 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.) Carrière) – 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.