Metabolomic responses of indigenous and nonindigenous plants to deer exclosure fencing and deer herbivory in a suburban forest

Trees and shrubs in suburban forest understories can be subject to chronic herbivory from abundant white-tailed deer. An undocumented consequence of this stress may be shifts in secondary metabolite production associated with defense. We aimed to learn whether plants protected from deer exhibited different metabolomic profiles compared to those exposed to deer. We tested the indigenous species Nyssa sylvatica and Lindera benzoin and the invasive, nonindigenous species Rosa multiflora and Euonymus alatus within a suburban forest understory in New Jersey, USA, in unfenced plots and plots fenced for 5.3 years. We did untargeted metabolomics by sampling leaves from three plants of each species per 6-7 fenced and unfenced plots, conducting chloroform-methanol extractions followed by LC-MS/MS, and conducting statistical analysis on Metaboanalyst. We also scored each species for deer browse frequency over eight years, and compared their heights and percent cover between unfenced and fenced plots. The analysis identified 2,333 metabolites. The global metabolome diverged significantly between fenced and unfenced plots pooled across species, but for individual species only N. sylvatica exhibited a significant fencing effect. Nyssa sylvatica was one of the most browsed species and was the only one with both greater cover and height in fenced plots, suggesting greater susceptibility to deer browsing. The metabolites most responsible for the fenced/unfenced divergence also were affected by the species-fencing combination, with increases in certain species but decreases in others. The most significant metabolites that were upregulated in fenced plants include some involved in defense-related metabolic pathways, e.g. monoterpenoid biosynthesis. Further study of more species in multiple sites is needed to learn how common metabolomic responses to deer are among forest species, how the intensity of deer pressure influences the responses, which types of metabolites are most affected, and if there are ecological consequences at the physiological, population, and/or community levels.

Fenced community gardens effectively mitigate the negative impacts of white-tailed deer on household food security

White-tailed deer (Odocoileus virginianus) are large herbivores that thrive in urban and peri-urban landscapes. Their voracious appetite and ubiquity have made deer a significant threat to growing food in home and community gardens; features that often make important contributions towards household food security. Focusing on food availability, stability, utilization, and access, I outline how white-tailed deer threaten household food security. Deer threaten availability of food by widely consuming plants grown for human consumption. Deer threaten stability of household food security by causing spatially and temporally unpredictable food losses. Deer threaten utilization of food, through acting as sources of food-borne pathogens (i.e. Escherichia coli O157:S7). Deer threaten access to food by necessitating relatively high-cost economic interventions to protect plants from browsing. Although numerous products are commercially available to deter deer via behavioural modification induced by olfaction and sound – evidence of efficacy is mixed. Physical barriers can be highly effective for reducing deer browsing, but often come with a high economic cost. Users of community gardens benefit from fencing by receiving shared protection against deer herbivory at a significantly lower per capita cost. Among many other benefits, fenced community gardens are useful in mitigating the threats of white-tailed deer to household food security.

Cost-benefit Quantification of Leaf Carbon Economics to Disentangle Responses of Plant Assemblages to Deer Herbivory

Although the plant carbon cost-benefit balance is known to be related to individual plant growth, reproduction, and population expansion, the association with plant community differences is not well understood. In this study, we examined how the leaf carbon cost-benefit metrics were associated with the assembly process of forest understory plant communities in areas highly affected by deer browsing. We calculated these metrics from plant physiologically parameters for 14 forest floor plant species growing in deer presence/absence site to detect the relationship between species dominance and leaf carbon cost-benefit metrics. As a result, the patterns of interspecific variation in benefit along the plant dominance rank differed in deer presence/absence sites, contributing to the marked differences in species composition and diversity observed at the two sites. In the absence of deer, where competition was the dominant determinant of plant community composition, carbon benefits among species were positively related to the plant dominance rank, indicating that species able to acquire more carbon were at an advantage. On the other hand, under deer herbivory, differences in carbon benefit between species were not strongly apparent and were not related to the plant dominance rank, indicating few differences in reproductive and expansion ability (plant fitness) between species. This process contributes to the high species diversity of plant communities observed in the presence of deer. Our results emphasize the possibility of connecting different fields of studies, physiological ecology, community ecology, and the plant carbon cost-benefit balance of single leaves to explain plant community composition differences.

Impacts of Forest Thinning and White-Tailed Deer Herbivory on Translocation of the Rare Terrestrial Orchid Platanthera integrilabia

Translocation is increasingly being used to supplement existing occurrences and establish new occurrences of rare plant species, but translocation success is dependent on understanding responses to habitat conditions and management. Platanthera integrilabia (white fringeless orchid) is a rare terrestrial orchid species presently found in mostly small occurrences that comprise a fraction of its historical distribution and abundance in the southeastern United States. We investigated the influence of shade and white-tailed deer herbivory, as cited concerns for this species, on the early success of its translocation from tubers as determined through measures of emergence, survival, growth, and reproduction of two cohorts. Our findings suggest that translocation from tubers could be a viable option to assist the conservation of P. integrilabia relative to its propagation from seed, but that low early emergence, survival, and flowering rates should be considered in translocation plans. Our results also indicate that translocation and ongoing habitat management should consider the potential for light availability to differentially impact distinct plant life stages and influence deer herbivory. We recommend that additional translocation studies designed to investigate the influence of site conditions on outcomes could improve the success of such efforts as well as inform the management of extant occurrences.