Evaluating the recovery of vegetation communities in Indiana state parks after over a decade of white-tailed deer population reduction

Background/Question/Methods

Although white-tailed deer (Odocoileus virginianus) were extirpated from Indiana by 1893, subsequent reintroductions of the species with regulated hunting and favorable landscape conditions have resulted in increased herd sizes state-wide.  This increased abundance was most pronounced in state parks where hunting was historically prohibited.  The 1990s saw the initiation of controlled hunts in twenty-one state parks, in part, to allow recovery of vegetation communities.  We used data collected from the controlled hunts to estimate pre-hunt deer abundance at each park.  In 2010, we resampled a network of vegetation plots established in 1996-97 across 15 state parks and four reference areas where hunting has been historically allowed.  Herbaceous percent cover was measured along three, 10 m line transects nested within each plot.  Percent cover data were used to calculate species richness (S), evenness (E), and Shannon-Weiner (H’) diversity trends between 1996/97 and 2010.  Nonmetric multidimensional scaling (NMS) ordination was used to examine composition changes between 1996-97 and 2010 and contemporary composition across environmental variables representing deer removed and hunter effort, changes in overstory structure, and topography.  Because plots were distributed across the state, NMS analyses were conducted by Indiana natural regions to control for variability in substrate and landscape context. 

Results/Conclusions

Based upon hunting data, estimated initial deer abundance ranged from 0.63 deer/ha in Brown County State Park to 8.92 deer/ha in Lincoln State Park.   Total deer reduction over all hunts ranged from 0.46 deer/ha in Shakamak State Park to 2.36 deer/ha in Harmonie State Park.  According to paired t-tests (α = 0.05), only two of the 15 parks exhibited significant increases in E.  However, S and H’ increased significantly in seven and eight parks, respectively.  Percent cover significantly increased in nine of the 15 parks.  NMS showed unidirectional movement in ordination space of herbaceous species composition through time for both parks and reference areas.  This suggests similar changes in composition between parks and reference areas since the study began.   A deer abundance index we developed (number of deer harvested/initial abundance/area of the park in ha)  and average harvest per hunter effort for the three most recent hunts showed a significant correlation (r² > 0.2) with one or more axes in four out of five natural regions.  This suggests that Indiana state park vegetation composition varies along a gradient related to changing deer population size.