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Forest composition and structure

Vanessa Fox, Dana Dudle, Bryan Helm, David Pope, and Aaron Randolph
Biology Department and Science Research Fellows, DePauw University
Summer 2004

In 2003, DePauw University acquired a 520-acre nature park, intended for the various purposes of habitat conservation, education, and recreation. The land comprises several habitats, including forest, old fields, wetlands, a river, and freshwater ponds, but the central feature of the land is a large limestone quarry that was abandoned 30 years ago. Each of these habitats has been significantly affected by human activity, through logging, farming, fishing and mining, and some areas are highly disturbed. Some central questions of restoration ecology – Are the ecosystems recovering on their own? Or is human intervention appropriate to promote recovery? If intervention is necessary, what kind? – form the core of our discussions about how DePauw should use and manage this resource.

Here we present baseline data describing several projects in the DePauw Nature Park during summer 2004. We established permanent grids marking study plots. Within the plots, we investigated the forest plant communities.

We set up study plots in three forested sites:  Arboretum (ARB), Quarry South (QS), and Quarry Hillside (QH).  We measured vegetation and habitat characteristics at ten randomly located plots in each site following BBIRD protocol.  Within a 5-m-radius subplot, we measured leaf litter depth and percent cover of understory vegetation and counted the number of shrubs and saplings (< 8.0 cm dbh) by species and size class.  Within an 11.3-m-radius subplot, we counted the number of live and dead trees (> 8.0 cm dbh) by species and size class.  

Results and Discussion
The three sites differed significantly in forest structure and composition.  These differences were surprising given the relative proximity of the sites. The history of human activity at the sites may provide a partial explanation for these differences.

The forest at the ARB was dominated by a mix of sugar maple, oaks, and hickories.  Ash, sugar maple, serviceberry, and spicebush were common in the understory.  The ARB forest had more large trees, more leaf litter, and fewer shrubs than the other sites.  Habitat at this site seemed to be representative of typical eastern deciduous forest.  However, the quality of habitat was somewhat degraded because of the small size of the forest and edge effects from adjacent land uses such as a powerline, agricultural fields, and athletic fields. 

The forest at QH was dominated by elm and sugar maple in the canopy.  Elm, cherry, and walnut were the dominant trees at QS.  Elm typically occurs along bottomland floodplains, and it seemed unusual for this species to be common in the interior of these hillside forests. We were surprised by the prevalence of both the walnut and cherry, especially at QS, given the history of extensive timber harvesting at the sites and the significant economic value of these two hardwood species.  Spicebush and coralberry, two species of native shrubs, were common in the understory at QH and QS.  The abundance of shrubs may be negatively affecting the potential for growth of tree seedlings in the forest understory. 

Overall, the forest habitat in the DePauw Nature Park provides valuable habitat.  We recommend that disturbance be minimized to maintain the integrity of the forest communities.  We also recommend that forest management practices proceed with caution. 

The sites provide an array of opportunities for research and coursework activities by students and faculty in ecology, plant biology, conservation biology, and environmental science.  We are excited about the opportunity for long-term studies at common sites, addressing questions within an interdisciplinary context.  Some of the questions we would like to address in future years include:

  • What biotic, abiotic, spatial, and historical factors contribute to the forest composition at the sites?

  • Are invasive plant species spreading in the sites?  Can we minimize the spread of invasive and non-native plant species in the sites? 

  • What is the recent history of the sites and how has human land use affected the biological communities?