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.

In recent decades, a paradigm shift in forest management and associated policies has led to greater emphasis on harvest practices that retain mature, overstory trees in forest stands that would otherwise be clear‐cut. While it is often assumed that the maintenance of compositional and structural complexity, such as that achieved through retention forestry approaches, will also mitigate negative impacts to functional diversity, empirical evidence of this relationship is sparse. We examined the effects of an aggregated retention system on taxonomic and functional diversity in a regenerating aspen‐dominated forest. Sampling was conducted along transects arranged to capture the transition from harvested (regenerating) forest to mature, unharvested forest (both intact forest stands and 0.1 ha retention aggregates). We then assessed the magnitude and distance of edge effects on multiple indices of taxonomic and functional diversity as well as functional identity. Twelve years after harvest, the distance and magnitude of edge effects on functional and taxonomic diversity did not differ between the two unharvested patch sizes (intact vs. aggregate); however, intact forest exhibited greater resistance to edge effects and greater depth of edge influence into harvested areas for some traits compared to aggregates. Analyses relying on functional traits were generally applicable across sites within a highly variable forest type, and our results demonstrate the promise of using functional traits to assess management impacts on plant diversity across a landscape. Aggregates maintained some functional attributes associated with interior forest and influenced adjacent regeneration. However, trends in some traits (i.e., shade tolerance and seed mass), particularly in the seedling layer, suggest aggregates of this size provide primarily edge habitat.

Retention harvesting, an approach that intentionally retains legacy features such as mature overstory trees, provides options for achieving ecological objectives. At the same time, retained overstory trees may compete with the nearby recovering understory for resources, and much remains to be learned about potential trade-offs with regeneration objectives, particularly over extended time periods. We assessed the influence of aggregated retention (reserved mature overstory and understory patches) versus intact forest on structure and productivity (standing biomass) of the adjacent woody understory and regeneration 12 years after harvest in northern Minnesota, USA. Each site was dominated by Populus tremuloides Michx., a species that regenerates prolifically via root sprouts following disturbance. Overall, fewer differences than expected occurred between the effects of intact forest and aggregated retention on regeneration, despite the small size (0.1 ha) of aggregates. Instead, harvest status and distance from harvest edge had a greater influence on structure and standing woody biomass. Proximity to aggregates reduced large sapling biomass (all species, combined) relative to open conditions, but only up to 5 m into harvested areas. This suggests the trade-off for achieving productivity objectives might be minimal if managers use retention aggregates in this region to achieve ecological objectives and meet management guidelines.