IMPACT OF OVERABUNDANT DEER ON NATIVE AND INVASIVE PLANTS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0216461
• Project Start Date: Oct 1, 2008
• Project End Date: Sep 30, 2011
• Program Code: [(N/A)]- (N/A)

Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853

Performing Department
Ecology & Evolutionary Biology

Non Technical Summary
Most residents in NY State have opinions about deer, some positive, some negative, and few that are neutral. Whether our stakeholders are land managers, hunters, gardeners, or environmental conservationists, the impact of deer on our local landscape is undeniable. Yet, surprisingly, there is less quantitative data on the impacts of deer on plant communities, and invasive species in particular, than is needed to make concrete recommendations. This proposed project aims to take quantitative data on the impact of deer on the spread of invasive weeds, the regeneration of forest on abandoned agricultural land, and the stability of native undisturbed forest communities. As such, the project fits squarely in the USDA applied research and extension priorities of Improving Management Practices for Sustainable and Compatible Agricultural, Natural Resource, and Energy Systems, including the prevention and control of aquatic and terrestrial invasive species. For example, our preliminary data suggests that deer may be quite effective at locally reducing invasive species abundance, but also that they may severely slow down the succession process because they favor native woody saplings. The benefits of excluding deer may be reversed depending on the specific land management goal. Thus, assessing the net impacts of deer on biodiversity via effects on recruitment of tree species, suppression of invasive, and consumption of natives is an important objective. Although most people have opinions about deer and their impacts, the specific effects they have are somewhat controversial in the scientific literature. This proposal aims to take quantitative data. I expect that a concrete outcome of our project could be the judicious use (or not) of fencing techniques by land owners and managers, depending on the desired effect. Although the exclusion of deer was previously seen as too expensive and impractical, landowners are increasingly mounting massive fencing projects, and the implications to the natural environmental community and for the spread of invasive plants is currently unknown. In central New York, we have already established replicated exclosures (50 x 50 feet each) in both abandoned agricultural lands and undisturbed forest, and this work will involve censuses of the plants and experiments to determine the impacts of deer on the soil ecosystem (including deposition of weed seeds). Deer have been proposed to have strong impacts on the plant biodiversity via preferential consumption of particular plant species, defecation of intact seeds, and indirect ecological effects. Our primary goal is thus to assess the impact of deer on the spread of weeds, the regeneration of forest, and recruitment of native species in the undisturbed forest. The practical information we generate will impact the landowner and manager community by offering specific data on the impact of deer on the environment.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0780	1070	10%
102	0613	1070	10%
136	0780	1140	15%
136	0613	1140	15%
214	0780	1140	25%
214	0613	1140	25%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 214 - Vertebrates, Mollusks, and Other Pests Affecting Plants; 136 - Conservation of Biological Diversity;

Subject Of Investigation
0780 - Grasslands, other; 0613 - Mixed conifer-broadleaf forests;

Field Of Science
1070 - Ecology; 1140 - Weed science;

Keywords

deer

herbivory

overgrazing

native plant community

invasive

Goals / Objectives
Over the next three years, I aim to study the impact of deer as drivers of exotic plant invasions in both post-agricultural habitats (old-fields reverting to forest) and primary forests that have never been plowed. In central New York, I have already established replicated exclosures (15x15 meters) in both habitat types, and this work will involve plant censuses, seed addition experiments, and an assessment of ecosystem processes (soil microbes, nutrients, and seed bank dynamics). Deer have been proposed to have strong impacts on the plant biodiversity via preferential consumption of particular plant species, defecation of intact seeds, and indirect ecological effects. The primary goal is thus to assess the impact of deer on the spread of weeds, the regeneration of forest, and recruitment of native species in undisturbed primary forest. Our ultimate goal is to work towards providing land managers quantitative information on the impacts of deer on plant biodiversity and invasive species.

Project Methods
I have established six pairs of deer exclusion and control plots in old fields located in Tompkins County where deer populations are dense (approximately/equal to 20 km -1). Plots are 15x15 meters and encircled by 2.7 meter tall wire mesh (400 cm 2 grid size). The control plots abut one wall of the treatment plots and a gate allows access to each cage. Importantly, the large mesh size and opening at the bottom of the gate door (approximately 25 cm tall) allows access by small and moderately sized mammals, but not deer. A similar experimental design (n=8) has been established in the Polson Reserve (Cornell Natural Areas, Ellis Hollow). Our approach involves three levels of analysis. First, in each year, we will conduct plant surveys using standard quadrate methods to assess the densities of native and invasive species. This is an intensive process that requires plant identification (about 50 species) and a team of 2-4 people. The data generated from these censuses is complex, requiring multivariate statistical methodologies. Secondly, each year soil samples will be taken to assess the impact of deer grazing on nutrients, microbes, and seed bank dynamics. The latter is critical to assess the long-term demographic impacts of deer on invasive plant species. Third, seed addition experiments (with key invasive and native woody species) and preference assays with the deer will lead to a more mechanistic understanding of the impacts of excluding deer. With these approaches I expect that we will be able to inform land managers as to the impacts of deer on invasive species spread and reversion of fields to forest.

Progress 10/01/08 to 09/30/11

Outputs
OUTPUTS: We have completed data collection on this project to assess the impact of overabundant deer on the success of native and invasive plants. We established four large-scale deer exclusion plots in a primary forest site (Cornell Natural Area, Poulson preserve) and six exclusion plots on abandoned agricultural sites (on Freese Road, Dryden). In these experiments we have engaged a postdoctoral fellow, a graduate student (who were provided summer support, and aided in experiments), two undergraduates, and a research support specialist. The data management part of this project is particularly intensive, as we are dealing with nearly comprehensive vegetation surveys for all plots. Four major results are evident. First, in the post-agricultural sites, woody plants are essentially absent in open deer-access plots, whereas substantial woody cover has already established in all of the exclusion plots. Thus, one potential outcome of this work is that deer may alter sucessional trajectories. Second, in the forest plots, we are not only monitoring the intact vegetation, but have also planted sentinel Trillium grandiflorum plants. These transplants serve as specific sentinels to directly test the impact of deer on the demography of a native plant. Surprisingly, there are no differences in the growth and likelihood of flowering of these sentinel trilliums. Third, we are currently working with the large vegetational dataset and anticipate writing a paper on the results in 2011-2012. Preliminary analysis indicates no difference in the relative abundance of native or invasive plants among our treatments. Nonetheless, our assessment of the seed bank has shown differences in the seed inputs to the soil. Thus, our tentative conclusion is that competitive and successional dynamics are taking priority over the reproductive effects seen in the seed bank. PARTICIPANTS: Anurag Agrawal (PI), Michael Stastny (former graduate student), John Parker (former postdoctoral associate), Emily Kearney (undergraduate), Ellen Woods (undergraduate), Amy Hastings (Research Support Specialist) TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
In New York, non-native plants are an important environmental and agricultural concern. Remarkably, it is unclear how overabundant deer are impacting the success of invasive plants. Our work is resulting in changes of knowledge (i.e., how deer shape plant community structure, success, and invasives) and, could eventually lead to a change in the actions of land managers. We have continued to cooperate with Prof. Bernd Blossey (Natural Resources), Toni Ditomasso (Crop and Soil Sciences), and Jay Boulanger (Cornell University Integrated Deer Research and Management Program) who have programs specifically targeted at dissemination of findings about the impacts of deer and invasive species. In particular, through working with the Cornell Plantations Natural Areas Committee, we have been working to understand and make recommendations about deer management as it relates to vegetation.

Publications

• Desurmont, G.A., Herard, F., and Agrawal, A.A. 2011. Oviposition strategy as a means of local adaptation to plant defense in native and invasive populations. Proc Royal Society Lond - Biological Sciences. In press.
• Desurmont, G.A., Donoghue, M.J., Clement, W.J., and Agrawal, A.A. 2011. Evolutionary history predicts plant defense against an invasive pest. Proceedings of the National Academy of Sciences USA 108:7070-7074.

Progress 10/01/09 to 09/30/10

Outputs
OUTPUTS: We have completed another field season of data collection on this project to assess the impact of overabundant deer on the success of native and invasive plants. We established four large scale deer exclusion plots in a primary forest site (Cornell Natural Area, Poulson preserve) and six exclusion plots on abandoned agricultural sites (on Freese Road, Dryden). In these experiments we have engaged a postdoctoral fellow, graduate students (who were provided summer support, and aided in experiments), two undergraduates, and a research support specialist. The data management part of this project is particularly intensive, as we are dealing with nearly comprehensive vegetation surveys for all plots. Thus far, two major results are evident. First, in the post-agricultural sites, woody plants are essentially absent in open deer-access plots, whereas substantial woody cover has already established in all of the exclusion plots. Thus, one potential outcome of this work is that deer may alter sucessional trajectories. In the forest plots, we are not only monitoring the intact vegetation, but have also planted sentinel Trillium grandiflorum plants. These transplants serve as specific sentinels to directly test the impact of deer on the demography of a native plant. We are currently working with the large vegetational dataset and anticipate writing a paper on the results in 2011. We have continued to cooperate with Prof. Bernd Blossey, who has an extension program specifically targeted at dissemination of findings about the impacts of deer and invasive species. PARTICIPANTS: Anurag Agrawal, Michael Stastny (former graduate student), Emily Kearney (undergraduate), Amy Hastings (Research Support Specialist) TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
In New York, non-native plants are an important environmental and agricultural concern. Remarkably, it is unclear how overabundant deer are impacting the success of invasive plants. Our work is resulting in changes of knowledge (i.e., how deer shape plant community structure, success, and invasives) and, could eventually lead to a change in the actions of land managers. We have continued to cooperate with Prof. Bernd Blossey, who has an extension program specifically targeted at dissemination of findings about the impacts of deer and invasive species.

Publications

• No publications reported this period

Progress 10/01/08 to 09/30/09

Outputs
OUTPUTS: We are in the first year of this major experiment to test how natural plant-produced chemical compounds defend plants against pests; our goal is to understand evolution of defense, which is a central question in ecology and applied plant protection. For the first time, we have been measuring natural selection and evolution (the response to selection in terms of changes in genotype frequencies) of plant chemical defenses following insect attack in a multi-year field experiment. We have established 16 replicate plots of evolving evening primroses (Oenothera biennis) and have begun to measure morphological, chemical and life history of the known genotypes. The influence of a major invasive pest (the caterpillar of the moth, Noctua pronuba) has proven to be a game-changing influence on our plots, and this is something we intend to study in 2010. Thus far we have engaged a postdoctoral fellow, a graduate student, undergraduate students, and a research support specialist. We anticipate data collection to continue through spring 2010 and we have scheduled a collaborators meeting for July 2010 to write up the first round of main findings of this experiment. PARTICIPANTS: Anurag Agrawal, Susan Cook (graduate student), Sergio Rasmann (postdoctoral fellow), Ellen Woods (undergraduate), Amy Hastings (Research Support Specialist) TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This has primarily been in the arena of change in knowledge. Not only has this work contributed to the fundamental building of new knowledge about the evolutionary ecology of plants defense against insects, but continuing work involves the study of a major invasive species. Additionally, this work is contributing to the training of postdoctoral fellows, graduate students, and several undergraduates.

Publications

• Johnson, M. T. J., Agrawal, A. A., Maron, J. L., and Salminen, J-P. 2009. Heritability, covariation and natural selection on 24 traits of common evening primrose (Oenothera biennis) from a field experiment. Journal of Evolutionary Biology 22:1295-1307.