| | Accession Number | 5004527 |
| | Title | Impacts of white-tailed deer on vegetation within parks in Montgomery County, |
| | Maryland: A statistical analysis of deer exclosure data collected during 1995-98 |
| | Project Description | The Maryland National Capital Park and Planning Commission, Montgomery County, Maryland |
| | (M-NCPPC) conducted a field study of the effects of white-tailed deer (Odocoileus virginianus) on |
| | the vegetation in several park locations during 1995-1998. The design of this study is described in |
| | the Request for Proposal (RFP) from M-NCPPC, dated 19 Dec 2000, and is summarized below. |
| | Eight 20 m x 20 m exclosures were set up with paired control plots at 8 park locations in 1995. |
| | Four additional plots without exclosures were set up in 3 parks. Within each of the larger plots, |
| | tree species, diameter at breast height (DBH), and vigor class were recorded for all individuals |
| | defined as trees by Storm and Ross (1992). Other measurements specified by Storm and Ross |
| | include seedling species, height class, and number of stems on four 2 m x 2 m subplots nested |
| | within each of the larger plots, shrub species and cm coverage (line intercept), herb/vine class, |
| | percent coverage, and maximum height class, summarized by 2 m x 2 m subplot, canopy |
| | measurements (four densiometer readings, one on each quarter of the 20 m x 20 plots), and |
| | browse measurements (species, browsed stems, recorded on transects of varying lengths, 1.7 m |
| | radius). One complication of this data set is caused by unequal sampling effort over years. In |
| | 1995, data were collected on all 20 m x 20 m plots, four 2 m x 2 m nested subplots, all the |
| | quarter plots of those nested subplots, and also some of the center 2 m x 2 m subplots. In 1996, |
| | however, only half of the 1 m x 1 m quarter subplots were measured. In 1997, only half of the 20 m |
| | x 20 m plots were measured, while in 1998, all 20 m x 20 m plots were measured, as well as four |
| | subplots, and all of the quarter plots of those subplots. Some statistical analyses can handle |
| | missing data, but they may not be as powerful and they may be more difficult to interpret. Another |
| | complication in this data set is the four additional 20 m x 20 m plots that were set up without |
| | exclosures. These data may cause problems for some analyses because the paired deer |
| | exclosures are missing from these plots. All attempts will be made to include these data in as |
| | many analyses as possible, but they may be eliminated from some analyses if complications are |
| | great. These plots will be included in some analyses, however, such as sample size calculations. |
| | The primary goal of this study is to test for differences in each variable between exclosed and |
| | control sites. The design warrants a repeated measures analysis of variance (ANOVA). Proc |
| | Mixed in SAS software (Littell et al. 1996) will be used to analyze this paired, repeated measures |
| | design, with the null hypothesis for each variable being no difference in vegetative growth and no |
| | change over time between exclosed study plots and the paired, unexclosed control sites. In |
| | particular, the density, height, and species diversity of seedlings will be analyzed, along with cover |
| | and species diversity of shrub layer, cover of the understory at various heights, and cover and |
| | diversity of ground vegetation. Other variables will also be analyzed. Diagnostics will include |
| | comparison of at least two variance covariance structures for the ANOVAs, testing of residuals for |
| | normality, and investigations of transformations and heteroscedasticity. Summary statistics of |
| | means and standard deviations (SDs), will be provided in tables for each variable analyzed and the |
| | relevant factors. Tukey pairwise comparisons of least square means will be used to sort out |
| | yearly differences in any variable for which year is significant (P < 0.05). If categorical variables are |
| | analyzed, Proc Genmod (Stokes et al. 1995) will be used to provide the analogous analysis to |
| | the paired, repeated measures ANOVA. To help with decisions about future data collection efforts, |
| | sample size (number of plots and subplots), size of plots, and the variables to be measured will |
| | be addressed. Sample size software (nQuery Advisor 4.0, Statistical Solutions) will be used to es |
| | Keywords | exclosure, montgomery county maryland, odocoileus virginianus, white-tailed deer, |
| | Principal | Jeff S Hatfield, USGS Patuxent Wildlife Research Center: jeff_hatfield@usgs.gov; |
| | Investigators |
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