Spatial Patterns of Irradiance and Advanced Reproduction along a Canopy Disturbance Severity Gradient in an Upland Hardwood Stand

Regeneration failure of Quercus in mature Quercus-dominated forests has been reported throughout the temperate zone. Quercus seedlings are often abundant in these forests, yet frequently fail to recruit to larger size classes despite canopy disturbances. To examine intra-stand patterns of advanced reproduction, competition, and irradiance in an upland Quercus stand, we installed a 2 ha plot that captured the canopy disturbance severity gradient caused by a wind event. To quantify disturbance severity and stand conditions, we inventoried all living and dead woody stems ≥5 cm diameter at breast height (dbh, 1.37 m above the surface) and quantified irradiance in 25 m2 quadrats (n = 800) using synchronized ceptometers. To inventory patterns of advanced reproduction within the plot, we recorded the species of every woody stem >1 m in height and <5 cm dbh. We also documented the species and height of every Quercus stem ≥0.5–<5 cm dbh and the species, height, and distance to each stem nearest the focal Quercus stem. At the genus-level, Quercus was the most common nearest neighbor. However, at the species-level, the most common nearest neighbors were Acer saccharum and Ostrya virginiana. Competition index values significantly differed by species (p < 0.01), but did not significantly differ by disturbance severity class and we found no significant interactions between species and disturbance class. Quercus advanced reproduction was significantly clustered through the study plot and cluster locations overlapped with clusters of high irradiance, but these patterns were scale-dependent. Our results indicate that an appreciation for intra-stand heterogeneity may improve forest management planning