When foraging optimally, mammalian herbivores should select food items that confer the greatest nutritional benefits (such as crude protein and non-structural carbohydrates) and impose minimal to no costs. Many plants defend themselves from herbivores by producing plant secondary metabolites (PSMs) that defend against herbivores. PSMs, such as tannins, deter herbivores by providing post-ingestive feedback cues that the forager experiences after a plant is consumed, and are therefore difficult for herbivores to avoid altogether. However, some PSMs such as terpenes are also volatile organic compounds (VOCs) that become gaseous at ambient temperatures and can be detected by herbivores via scent prior to ingestion. PSMs that can be detected prior to ingestion prevent herbivores from consuming a plant to begin with, and enable herbivores to avoid incurring costs while foraging. Our objective was to discern if the foraging preferences of white-tailed deer, a near ubiquitous herbivore in North America, were influenced by the nutritional (crude protein and non-structural carbohydrates) or anti-nutritional (tannin and polyphenol) constituents of trees during summer and winter. We also determined if the VOCs that were emitted by trees influenced the forage selection of deer by providing pre-ingestive cues. During summer, we found that deer preferred trees with a high non-structural carbohydrate content. During winter, deer preferred trees with a low crude protein content and a high tannin content. After sniffing trees that emitted a large proportion of monoterpenes and sesquiterpenes, deer were averse to begin foraging. In the few instances when deer foraged trees with high terpene contents, they consumed less than they did from low terpene trees. Our results suggest that VOCs, a long overlooked aspect of foraging ecology, may play a larger role in determining which plant species herbivores will avoid than the nutritional and anti-nutritional constituents of plants.

This research aims to identify the processes that influence the structure of eastern redcedar (Juniperus virginiana L.) stands across a range of size classes and in stands that are co-dominated by deciduous species. The trend of eastern redcedar encroachment into prairies and old fields in North America is well-documented; but the mechanisms that shape the distribution of con- and heterospecific trees within stands are poorly understood. Eastern redcedar stands representing a variety of size classes were sampled in the Midwest to examine how stand-shaping processes vary with stand age. Additionally, mature eastern redcedar stands where Quercus spp. are codominant were sampled to evaluate how competitive interactions influence stand structure. Point-pattern analyses were conducted to detect signals of underlying point-processes. We found several signals of density-dependent growth including evidence of self-thinning and regular-spacing between mature individuals. We found segregation within and between mature eastern redcedar and Quercus spp., indicating competitive partitioning of space. These findings indicate density-dependent intra- and interspecific competition are the most important process influencing the structure of eastern redcedar stands in its encroaching range.

1. The encroachment of woody plants into grasslands is an ongoing global problem that is largely attributed to anthropogenic factors such as climate change and land management practices. Determining the mechanisms that drive successful encroachment is a critical step towards planning restoration and long-term management strategies. Feedbacks between soil and aboveground communities can have a large influence on the fitness of plants and must be considered as potentially important drivers for woody encroachment. 2. We conducted a plant-soil feedback experiment in a greenhouse between eastern redcedar Juniperus virginiana and four common North American prairie grass species. We assessed how soils that had been occupied by redcedar, a pervasive woody encroacher in the Great Plains of North America, affected the growth of big bluestem, little bluestem smooth brome, and western wheatgrass over time. We evaluated the effect of redcedar on grass performance by comparing the height and biomass of individuals of each grass species that were grown in live or sterilized conspecific or redcedar soil. 3. We found that redcedar created a negative plant-soil feedback that limited the growth of two species. These effects were found in both live and sterilized redcedar soils, indicating redcedar may exude an allelochemical into the soil that limits grass growth. 4. Synthesis. By evaluating the strength and direction of plant-soil feedbacks in the encroaching range, we can further our understanding of how woody pants successfully establish in new plant communities. Our results demonstrate that plant-soil feedback created by redcedar inhibits the growth of certain grass species. By creating a plant-plant interaction that negatively affects competitors, redcedars increase the probability of seedling survival until they can grow to overtop their neighbors. These results indicate plant-soil feedback is a mechanism of native woody plant encroachment that could be important in many systems yet is understudied.