White-Tailed Deer are a Biotic Filter During Community Assembly, Reducing Species and Phylogenetic Diversity

Community assembly entails a filtering process, where species found in a local community are those that can pass through environmental (abiotic) and biotic filters and successfully compete. Previous research has demonstrated the ability of white-tailed deer (Odocoileus virginianus) to reduce species diversity and favour browse-tolerant plant communities. In this study, we expand on our previous work by investigating deer as a possible biotic filter altering local plant community assembly. We used replicated 23-year-old deer exclosures to experimentally assess the effects of deer on species diversity (H′), richness (SR), phylogenetic community structure and phylogenetic diversity in paired browsed (control) and unbrowsed (exclosed) plots. Additionally, we developed a deer-browsing susceptibility index (DBSI) to assess the vulnerability of local species to deer. Deer browsing caused a 12 % reduction in H′ and 17 % reduction in SR, consistent with previous studies. Furthermore, browsing reduced phylogenetic diversity by 63 %, causing significant phylogenetic clustering. Overall, graminoids were the least vulnerable to deer browsing based on DBSI calculations. These findings demonstrate that deer are a significant driver of plant community assembly due to their role as a selective browser, or more generally, as a biotic filter. This study highlights the importance of knowledge about the plant tree of life in assessing the effects of biotic filters on plant communities. Application of such knowledge has considerable potential to advance our understanding of plant community assembly

Vegetation_Metadata_2014

Detailed descriptions of columns and data formatting used in Cover_Data_2014.csv, Seedling_Data_2014.csv, and Tree_Data_2014.cs

Soils_Data_2014

Soil nutrient data for both organic and mineral soil horizons at 24 sites in Rothrock and Bald Eagle state forests in central Pennsylvania. See Soils_Metadata_2014.csv for descriptions of each column, including extraction methods (Kellogg Soil Science Laboratory, Lincoln, Nebraska, USA)

Seedling_Data_2014

Understory tree seedling data (<1 inch dbh) by height class in Rothrock and Bald Eagle state forests in central Pennsylvania. See Vegetation_Metadata_2014.csv and Species_Code_List.csv for specific column descriptions and data formatting

Understory plant cover data 2014

Understory plant data by percent cover, average height, and count for 24 sites across Bald Eagle and Rothrock state forests in central Pennsylvania. See Vegetation_Metadata_2014.csv for specific column descriptions and data formatting

Soils_Metadata_2014

Detailed descriptions of variables in Soils_Data_2014.cs

Evaluating Inter-Rater Reliability and Statistical Power of Vegetation Measures Assessing Deer Impact

Long-term vegetation monitoring projects are often used to evaluate how plant communities change through time in response to some external influence. Here, we evaluate the efficacy of vegetation monitoring to consistently detect changes in white-tailed deer browsing effects. Specifically, we compared inter-rater reliability (Cohen&#8217;s &#954; and Lin&#8217;s concordance correlation coefficient) between two identically trained field crews for several plant metrics used by Pennsylvania state agencies to monitor deer browsing impact. Additionally, we conducted a power analysis to determine the effect of sampling scale (1/2500th or 1/750th ha plots) on the ability to detect changes in tree seedling stem counts over time. Inter-rater reliability across sampling crews was substantial for most metrics based on direct measurements, while the observational based Deer Impact Index (DII) had only moderate inter-rater reliability. The smaller, 1/2500th ha sampling scale resulted in higher statistical power to detect changes in tree seedling stem counts due to reduced observer error. Overall, this study indicates that extensive training on plant identification, project protocols, and consistent data collection methods can result in reliable vegetation metrics useful for tracking understory responses to white-tailed deer browsing. Smaller sampling scales and objective plant measures (i.e., seedling counts, species richness) improve inter-rater reliability over subjective measures of deer impact (i.e., DII). However, considering objective plant measures when making a subjective assessment regarding deer browsing effects may also improve DII inter-rater reliability

Species_Code_List_2014

List of species names for abbreviation codes used in Tree_Data_2014.csv, Seedling_Data_2014.csv, and Cover_Data_204.cs

Data from: Soil chemistry, and not short-term (1-2 year) deer exclusion, explains understory plant occupancy in forests affected by acid deposition

The loss of species diversity and plant community structure throughout the temperate deciduous forests of North America have often been attributed to overbrowsing by white-tailed deer (Odocoileus virginanus). Slow species recovery following removal from browsing, or reduction in deer density, has been termed a legacy effect of past deer herbivory. However, vegetation legacy effects have also coincided with changes to soil chemistry throughout the northeastern United States. In this paper, we assess the viability of soil chemistry (i.e. pH, extractable nutrients, and extractable metals) and other factors (topography, light, overstory basal area, and location) as alternative explanations for a lack of vegetation recovery. We compared the relative effects of soil chemistry, site conditions, and short-term (1-2 year) deer exclusion on single-species occupancy probabilities of 10 plant taxa common to oak-hickory forests in central Pennsylvania. We found detection for all modeled species was constant and high (p > 0.65), and occupancy probability of most taxa was best explained by at least 1 soil chemistry parameter. Specifically, ericaceous competing vegetation was more likely to occupy acidic (pH < 3.5), base cation poor (K < 0.20 cmolc/kg) sites, while deer-preferred plants were less likely to occur when soil manganese exceeded 0.1 cmolc/kg. Short-term deer exclusion did not explain occupancy of any plant taxon, and site conditions were of nominal importance. This study demonstrates the importance of soil chemistry in shaping plant community composition in the northcentral Appalachians, and suggests soil as an alternative, or additional, explanation for deer vegetation legacy effects. We suggest that the reliance on phyto-indicators of deer browsing effects may overestimate the effects of browsing if those species are also limited by unfavorable soil conditions. Future research should consider study designs that address the complexity of deer forest interactions, especially in areas with complex site-vegetation histories

Tree_Data_2014

Overstory tree measurements (>=5" dbh) at 24 sampling sites at Rothrock and Bald Eagle state forests in central Pennsylvania. See Vegetation_Metadata_2014.csv and Vegetation_Metadata_2014.csv for specific column descriptions and data formatting