Harvard Forest Research

Testing the role of source-sink dynamics in the invasion of garlic mustard in the New England understory

Principal Investigator: Kristina Stinson
Harvard Forest: Jan 01 2005 - Jan 01 2010:

Abstract:
Garlic mustard, Aliaria petiolata, is an invasive understory herb that has spread through much of North America and is listed as a threat to forest understory herb communities in several states. In New England, garlic mustard exhibits regional differences in its ability to dominate the forest understory. The proposed research examines why some populations of garlic mustard are invasive in the understory and others are not. In particular, we will quantify the importance of regionally variable environmental factors and population differences on source-sink dynamics and demographic self-sustainability of understory garlic mustard populations that vary in their degree of invasiveness. Using a combination of 1) population-level studies and quantitative genetics, 2) meta-population manipulations and observations, and 3) landscape level spatial and historical analysis, we aim to determine the importance of open-canopy populations of garlic mustard to maintaining understory populations and contributing to the geographic spread of garlic mustard. The population level studies will a) distinguish whether regionally variable environmental factors and/or regional differences among populations account for variation in garlic mustard invasion, b) test whether source population effects, such as adaptation to open- or closed-canopy conditions or maternal environmental effects, enhances or diminishes performance in understory conditions, and c) identify specific traits associated with performance under different conditions. The metapopulation studies will experimentally manipulate the contribution of open-canopy sources to understory populations and monitor demographic consequences of such manipulations. The landscape historical studies will test whether the spatial distribution of past open-canopy sites can help explain current distributions of garlic mustard. This latter component of the study makes use of data, newly available from a collaboration between The Nature Conservancy and Harvard Forest researchers, regarding forest harvesting and land-use history across New England. Results of this research will contribute practical and immediately applicable information on the types of populations of garlic mustard that are likely to be most problematic and will give guidance to establishing eradication priorities. The research has the potential to identify particularly aggressive genotypes and characterize the phenological and physiological responses that render them aggressive. This study will identify which environmental settings are most susceptible to invasion by identifying present and historical factors that are associated with current garlic mustard presence. This is a collaboration between a forest ecologist with extensive experience in historical data analysis at a regional scale (Foster) and evolutionary population biologists (Donohue and Stinson). The research will be conducted at an LTER site (The Harvard Forest), making possible the continuation of longer-term observations of experiments established in this research program. In addition, the research contributes to a collaborative effort of the Harvard Forest, the Nature Conservancy, and Massachusetts state agencies to monitor and eradicate invasive plant species. Thus the results of this study will have direct conservation implications and direct avenues for implementation of results.
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