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Forest composition and health

Kyra Reed and Vanessa Fox
Biology Department, DePauw University
Summer 2005

DePauw University’s Nature Park contains a variety of habitats, including deciduous forests, early successional meadows, wetlands, a river, several freshwater ponds, and a large abandoned limestone quarry – all of which have been affected by human activity. However, in managing the park, it is important to maintain the integrity of the ecosystem and promote forest recovery. Previous studies on forest composition have been done in the Nature Park, but an assessment of the relative health of the forest, in comparison to older, less disturbed forests, has not been conducted.  Here we present baseline data on the ecological composition and health of forested sites in the park.  We assessed the relative health of the forest by analyzing stand structural diversity, tree composition, and forest regeneration.  We compared the vegetation data to a characteristic healthy older forest in Ohio as our model.  This information can allow us to make recommendations on future management strategies to promote and sustain forest health. 

We hypothesized that some of the forests in the Nature Park will display characteristics of a less healthy, younger forest as a result of recent human activity.  

We assessed vegetation characteristics at three forested sites, ARB, QH, and QS, in the DePauw Nature Park using randomly selected plots.  Within a 5-m radius plot, we estimated leaf litter depth, estimated percent cover of understory vegetation, and counted the number of shrubs and saplings by species and size class.  Within an 11.3-m radius plot, we counted the number of trees by species and size class.  We used an increment borer to extract a core and estimate the age of a subsample of trees from each sites.  We compared our results to data that were collected in Ohio using the same methods. 

The forested sites in the Nature Park varied extensively in vegetation composition and structure, despite the relative closeness of our sites. The forests also differed substantially from that of the Ohio sites.  Native shrubs form the bulk of the understory vegetation at the sites.  Coralberry, a native shrub, dominates the understory vegetation at two of the sites, QH and QS.  The dense growth of shrubs may be outcompeting tree seedlings and thus deterring regeneration.  The composition of trees at one of the sites, ARB, and the Ohio sites is characteristic of eastern deciduous forest, with large proportions of oak, sugar maple, and hickory.  The forest at QH and QS consists of higher proportions of elm and lacks oak and hickory.  The forest at QS contains more small trees and fewer large trees than the other sites.  The trees at the ARB have a wider range of ages (40 to 100 years old) than trees at QH (50 to 60 years old) and QS (30 to 50 years old).  Trees at the Ohio sites ranged from 100 to 120 years old.

Our data suggest that the forested sites at QH and QS may be in relatively poor health compared to the ARB and Ohio sites.  These forests may maintain themselves, but contain a large proportion of shrubs relative to seedlings.  Competition in the understory may limit growth of tree seedlings.  Also, oak and hickory, typical overstory trees in the region, are rare at QH and absent at QS.  One option to improve the health of the forests in the Nature Park is to remove excess shrubs in the understory and open up resources for tree seedlings.  Over time, the forests may begin to resemble mature, healthy forests.  A healthy forest would improve the quality of habitat for plants and animals and would be more aesthetically pleasing to park visitors.  We recommend continued monitoring of the forests in the Nature Park to observe changes in the forest composition and health over time.