Plant Community Responses to Silvicultural Opening Size Across and Between Gaps in Wisconsin Northern Hardwood Forests

Abstract

Within northern hardwood forests, gap-creating disturbances alter the resources available to understory vegetation. Levels of diversity following disturbance are expected to vary based on the size of the created gap. One mechanism of understanding this overall diversity is the Gap Partitioning Hypothesis (GPH), which proposes that a variation in resource availability allows for species specialization. My hypothesis is that as gap size increases, diversity levels should parallel this increase until the full gap heterogeneity has been attenuated. However, other biotic factors may decouple this hypothesis, such as the presence of clonally reproducing shrubs (example Rubus strigosus). I tested this theory in medium-sized (20-meter diameter) and large-sized (46-meter diameter) gaps in a northern hardwood forest of northern Wisconsin. Understory competition and abundance was assessed in the summer of 2008 in this forest in 1 square-meter plots which were previously established within gaps which were created approximately thirteen years ago. Preliminary analyses show that overall, intermediate gap sizes tended to be more diverse than the larger gap sizes. Diversity levels tended to be lower than predicted due to the dense population of Rubus strigosus in the larger, and to an extent, the medium-sized, gaps. This study shows that gap size is important to floristic diversity, but that additional interacting factors, such as shrub presence, play just as significant a role. The herbaceous understory can be used as an indicator for supporting forest function, which underlines the importance of understanding this ground-level diversity as a tool to increase the diversity and health of the rest of the forest stand.