Tree Regeneration in a Southwestern Indiana Forest: Implications of Long-Term Browsing by Deer

Abstract

Wesselman Woods Nature Preserve (WWNP) has never been subjected to timber harvest. However, deer can completely penetrate WWNP and browse tree seedlings and saplings throughout the forest. In this study, 30 plots (20 X 30 m) were surveyed (1.8 ha total). All trees of every size were identified
and categorized into one of four strata based on height—herb layer, shrub layer, midstory, and overstory. Using the Shannon-Weiner Diversity Index, diversity was compared across strata. In the midstory 95% of stems over 150 cm in height and with a dbh < 5 cm) were pawpaws (3841 of 4038 stems). Sugar maples comprised 101 of the remaining midstory trees, and only three other species had more than 10 trees in this stratum. Oak trees had been almost completely lost from the midstory. Given its poor representation of canopy species, the midstory layer had significantly lower diversity compared to other strata. Many tree species (including sweetgum, tulip poplar, blackgum, hackberry, and 12 species of oak) have not transitioned into the midstory stratum, suggesting that regeneration of these species into the overstory is limited. In addition, pawpaw appears to have formed a recalcitrant layer and is anticipated to limit forest regeneration even more. While the patterns observed in this survey suggest that forest regeneration may be constrained by deer browsing at WWNP, an experimental study would be needed to confirm that deer (versus other factors, such as fire suppression or shading conditions of the forest) are responsible for limited regeneration. Placed within a forest management perspective, we discuss one possible experiment to examine concerns related to deer browsing and overabundance of pawpaw trees.