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Harvard Forest Symposium Abstract 2015

  • Title: Garlic mustard effects on landscape-scale temperate forest plant assemblages
  • Primary Author: Kristina Stinson (University of Massachusetts - Amherst )
  • Additional Authors: Jason Aylward (Harvard Forest); Dustin Haines (University of Massachusetts - Amherst )
  • Abstract:

    It is well established that invasive plants can alter species composition and diversity as well as ecosystem function in communities that they invade. Whether and how species of similar ecosystems respond in predictable ways to invasion at the landscape scale is less understood. For instance, there are few studies documenting whether northeastern forest understory plant communities show similar compositional shifts in the presence of invasive plants. Studies that compare invaded and non-invaded communities at the landscape scale are critical for making broader ecological interpretations about the invasion process and its potential to disrupt native community structure. In addition, this approach can help guide invasive plant management, which is frequently done on an ad-hoc basis at a local (parcel) scale. We studied the effects of the widespread invasive plant, garlic mustard (Alliaria petiolata), on eight different parcels of northeastern forest understory plant communities over two years (2013-2014), including Harvard Forest. Plant species composition, functional group identity, and species densities were contrasted with garlic mustard presence and abundance across invaded and similar non-invaded plots using univariate and multivariate analyses. These analyses were used to assess the degree of site-specificity vs. generalizable patterns of plant community assembly in the presence or absence of the invasive.

    Garlic mustard presence and parcel had a strong influence on plant species community structure in both years. Shannon species diversity was greater in invaded compared to non-invaded areas in summer 2013 and spring 2014. This relates in part to garlic mustard frequently being accompanied by invasive woody species, except at Harvard Forest where the opposite occurred. When analyzed by plant functional group, plant communities in non-invaded areas were distinct from those in invaded areas. Overall plant species composition, however, was driven by parcel rather than invasion status. We conclude that garlic mustard invasion can result in recognizable assemblages of plant species that are maintained at the landscape scale. These communities are less species rich than their non-invaded counterparts and also are more likely to host one or more woody invasive species. However, the clustering of plant communities by parcel also suggests the importance of site-specific conditions, and that management practices should reflect these differences as opposed to using a one size fits all approach for managing garlic mustard invasions.

  • Research Category: Invasive Plants, Pests & Pathogens