PS 51-52 - Fine scale spatial variation in woody regeneration following ecologically based timber harvest

Thursday, August 10, 2017
Exhibit Hall, Oregon Convention Center
Skye M. Greenler, Forestry and Natural Resources, Purdue University, West Lafayette, IN and Michael R. Saunders, Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN

Canopy heterogeneity results from inherent landscape characteristics, such as slope, aspect, and soil type, and from transient environmental conditions created by weather and by natural and anthropogenic disturbances. In particular, disturbances dramatically alter the forest understory microenvironment, causing compositional shifts in the regeneration layer that influence the future forest canopy. However, the historic disturbance regime and the resulting understory conditions that led to current overstory communities are no longer observable or measurable, making them difficult to recreate. Silvicultural methods that strive to directly emulate, or even incorporate aspects of, a system’s natural disturbance regime can regenerate diverse stands with high ecological and economic value. Following silvicultural harvest, light levels increase both within the harvest opening and surrounding forest matrix, creating altered understory conditions that extend far beyond the harvest boundary. Using transect-based surveys, we studied how orientation (N, E, S, W) within and outside of small shelterwood harvest gaps influenced seedling spatial distribution in four factorial treatments: 2- or 3-stage group shelterwood, with or without prescribed fire in southern Indiana.


Two years after harvest, we found the spatial distribution of competitive (>30 cm tall) Quercus spp., Carya spp., and Sassafras albidum seedlings were dependent on the interaction between location (within or outside the harvest opening), and orientation. Competitive Quercus spp. seedlings were five to seven times more abundant in the forest matrix on the northern and western sides of shelterwood harvests than in the southern forest matrix. Sassafras albidum regeneration was generally higher within the harvest than the surrounding matrix, but was notably highest in the northern matrix, where maximal light filtered through the shelterwood opening into the matrix understory. Liriodendron tulipifera abundance was ten times higher within the harvest gap and than the surrounding forest matrix with no effect of cardinal direction. Predicting fine scale regeneration patterns can inform arrangement of harvest areas and direction of limited resources for post harvest management. More broadly, understanding how regeneration varies spatially in and around forest canopy openings is critical to reconstructing how past disturbances shaped current overstory composition and how present management will influence composition and heterogeneity of future forests.