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Harvard Forest Symposium Abstract 2016

• Title: Long-term metapopulation dynamics for the invasive Alliaria petiolata
• Primary Author: Kristina Stinson (University of Massachusetts - Amherst )
• Additional Authors: Laura Hancock (Christopher Newport University)
• Abstract:

  1) Background/Question/Methods
  
  Alliaria petiolata (garlic mustard) is an invasive herb in North America. In its native range, garlic mustard is found in disturbed edge habitats. In recent decades, garlic mustard has been observed to be rapidly invading intact forest understories – a novel habitat type. Different selection pressures between habitats could select for different traits within garlic mustard populations, leading to divergence in characteristics and demography over time. This novel study examines a metapopulation of garlic mustard distributed across forest edge, intermediate, and forest understory habitat types over a long-term time scale (13 years). We conducted a metapopulation field survey at the Harvard Forest (Petersham, MA) from 2003-2006, and again in 2015 across a habitat gradient – forest edge, intermediate forest, and forest interior – to determine densities and characteristics of garlic mustard in each habitat type. Our study investigates whether 1) there are differences in functional and fitness-related traits (height and number of fruit per plant) over time and between microhabitat types, 2) the edge habitat type supports higher densities of immature and reproductive adults than intermediate or forest understory habitat types, and 3) densities for immature and reproductive adults are increasing, stable, or in decline in each habitat type over a long time scale.
  
  2) Results/Conclusions
  
  Fruit production per plant was similar from 2003 to 2006. Fruit production per plant was highest in the edge habitats. Likewise, plant height was similar within habitats across years. The edge habitats always had significantly taller plants compared to both intermediate and forest understory populations. Immature garlic mustard density was generally higher in the edge habitats than in the forest and intermediate habitats within the same year. Reproductive adult densities were generally similar between all habitat types within the same year; unlike immature plants, edge habitat types did not have higher adult densities. There was also high interannual variability in adult densities within habitat types. Density data from 2003, 2004, and 2005 data suggest the metapopulation appears to be following a biennial life-stage cycle characteristic to garlic mustard. Our results suggest general declines in reproductive adult densities in forest and intermediate habitats, since 2015 should have been a peak adult density year. Reproductive adult densities in edge habitat types have been similar over the 13-year period, showing little long-term variation, suggesting populations in edge habitats are not in decline. Since these edge habitats also produce the most fruit, we speculate that these populations represent the source, and the forest populations may not be sustainable over the long-term. We will continue metapopulation and functional and fitness trait surveys in 2016 to establish a more complete picture of population dynamics in this invasive species.
  
  

• Research Category: Invasive Plants, Pests & Pathogens