Spatial patterning of underrepresented tree species in canopy gaps 9 years after group selection cutting

• We investigated spatial patterning of regeneration in canopy gaps.
• Forty-nine harvest gaps were evaluated 9 years after group selection cutting.
• Southern gap edges contained the greatest aggregations of desired species.
• Spatial patterning of desired species should inform silvicultural system design.

Group selection and gap-based silvicultural systems are often proposed to promote compositional and structural heterogeneity across forest landscapes. The gap environment creates gradients of resources, especially light and moisture, that are important for maintaining and enhancing tree species diversity. To advance understanding of spatial variability of tree regeneration in forest gaps, seedlings and saplings of yellow birch (Betula alleghaniensis Britton) and eastern hemlock (Tsuga canadensis (L.) Carrière) were mapped in 49 group-selection openings with diameters of 1, 1.5, and 2 times canopy tree height (22 m), 9 years after the openings were created. We used Ripley’s K, kernel density estimates, and raster-based local statistics to analyze spatial point patterns. Our results indicate that spatial patterns in the openings were mostly aggregated. The southern edges of the largest openings contained the highest magnitude of yellow birch and eastern hemlock per unit area. Moisture availability and opening size appear to be important factors underlying regeneration success in this study. Over time, the spatial patterns of these species may shift as the southern locations become less suitable for the shade mid-tolerant yellow birch. Continued monitoring and additional treatments, such as gap expansion along southern borders, will likely be necessary in order to ensure underrepresented species successfully reach maturity.