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.

The Northern White-Cedar Recruitment Bottleneck: Understanding the Effects of Substrate, Competition, and Deer Browsing

Research Highlights: Regenerating northern white-cedar (Thuja occidentalis L.) is challenging throughout much of its range. This study attempts to relate differences in natural regeneration to stand- and seedbed-level factors. Background and Objectives: Lack of regeneration of northern white-cedar is often attributed to overbrowsing by white-tailed deer (Odocoileus virginianus Zimmerman) because white-cedar is a preferred winter browse species. However, there are many other factors that may contribute to regeneration failure for white-cedar including its specific seedbed requirements and competition from other, often faster-growing trees and shrubs. Materials and Methods: We surveyed five mature white-cedar stands in Wisconsin, USA that have had little to no management in the past 50+ years to find stem densities of natural white-cedar regeneration in three height classes. We also collected data at each stand on potential predictor variables including overstory attributes, competitive environment, seedbed, and browsing by deer. We used model selection to create separate models to predict stem density of each white-cedar regeneration height class. Results: None of the measures of deer browsing used in this study were found to be associated with white-cedar regeneration. Soil pH, competition from other seedlings and saplings, and stem density of white-cedar in the overstory were found to be potentially associated with white-cedar regeneration. Conclusions: While browsing by deer is likely a factor affecting white-cedar regeneration in many areas, this study highlights the challenge of quantifying deer browse effects, as well as showing that other factors likely contribute to the difficulty of regenerating white-cedar.

Positive Beispiele der Wald-Wild-Situation bei der Weisstannenverjüngung

Positive examples of forest-ungulate situations focusing on silver fir regeneration Roe deer, chamois and red deer browse on the apical shoots of young trees, and particularly selected are those of the European silver fir. Because of this selective feeding of ungulates, the silver fir is unable to sustain its population density relative to other tree species. However, due to locally functioning forest-ungulate situations, there have been areas of improved silver fir regeneration during the last few years. In this study, twenty different sites exhibiting such improvement have been analysed. Eighteen sites were situated in thirteen different Swiss cantons, as well as one each in Germany and Austria. With the aid of interviews with experts such as local foresters, gamekeepers, hunters and representatives of the cantonal departments of hunting and forestry, the importance of sixty-six potential influencing factors on a locally improved forest-ungulate system has been investigated. Frequency analysis has shown that the density of roe deer, the availability of light and the presence of lynx are the most important of these factors. But also the density of chamois, the increased focus on a natural regeneration and the form of management have been frequently mentioned as central factors. Changes in communication between the hunting and forestry sides have been considered most often as central or important. Positive examples could be examined in all regions of Switzerland – in cantons with patent hunting and hunting districts as well as in areas with different densities and compositions of wild ungulates. It does not seem that a single influencing factor, but rather a combination of different factors was decisive for improved silver fir regeneration.

White-tailed deer browse preference for an invasive shrub, Amur honeysuckle (Lonicera maackii), depends on woody species composition

Selective browsing by abundant, generalist herbivores on preferred species could allow less-preferred invasive species to flourish. We tested such an effect by examining rates at which white-tailed deer (Odocoileus virginianus Zimmermann) consume Amur honeysuckle [Lonicera maackii (Rupr.) Herder], an invasive shrub, relative to native woody species across eight forested sites in southwestern Ohio. We tested three hypotheses: (1) deer prefer to browse on L. maackii versus other woody plants; (2) L. maackii is not a preferred source of browse, but is consumed where preferred foods are scarce; and (3) L. maackii provides an important food resource for deer in early spring when other foods are scarce. We used counts of browsed and unbrowsed twigs of each species to calculate, for each site, both the proportion of each species’ twigs browsed and the degree to which deer selectively favor each species (“electivity”) during early to mid-growing season. Across the eight sites, electivity of L. maackii correlated with the proportion of its twigs browsed, and both measures were negatively associated with the density of L. maackii twigs. Lonicera maackii electivity was negative at most sites, indicating it is generally not preferred, undermining hypothesis 1. The hypothesis that deer consume L. maackii when more-preferred foods are depleted was not supported, as there was no negative relationship between L. maackii browse and the density of twigs of more-preferred species. We found a negative relationship between the proportion of L. maackii twigs browsed and the density of L. maackii among sites, which supports the third hypothesis. This finding, combined with seasonal patterns of deer browse on L. maackii, indicates that this invasive shrub is an important source of browse for deer during early spring, regardless of its abundance.

Impact of White-Tailed Deer (Odocoileus virginianus Zimmerman) on Ornamental Plants in Alabama Green Industries and Home Landscapes

Nursery and landscape professionals as well as homeowners throughout Alabama continue to experience deer damage to ornamental plants due to the increasing populations of white-tailed deer (Odocoileus virginianus Zimmerman). To understand the extent of damage, surveys were created for green industry professionals and homeowners. The industry survey was sent to members of the Alabama Nursery and Landscape Association (ALNLA) (N = 223). The homeowner survey was sent to nine Master Gardener associations and administered through one day of onsite surveys at Huntsville Botanic Garden (N = 668). Questions inquired if respondents encountered injury to plants from whitetail deer, what types of preventive methods they were using, plants typically browsed, and extent of plant loss annually as a result of deer activity. Fifty-five percent of green industry professionals and 37% of homeowners answered ‘yes’ to damage problems, and of those, more homeowners (61%) than industry (41%) employed preventive methods to reduce deer browse. High fencing, electric fencing, Liquid Fence® repellent, and motion irrigation were the most effective of eleven preventive measures listed. Indian hawthorn (Rhaphiolepis indica L.) and hosta (Hosta spp.) were the most commonly damaged plants according to industry and homeowners, respectively. The majority of homeowners experienced damage during the spring, while industry participants reported most damage during the winter and fall months.