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Harvard Forest Symposium Abstract 2019

• Title: Trait variation and long-term population dynamics of the invasive Alliaria petiolata across three growth microhabitats
• Primary Author: Laura Hancock (University of Massachusetts - Amherst )
• Additional Authors: Kristina Stinson (University of Massachusetts - Amherst )
• Abstract:

  Long-term population dynamics across heterogenous environments could be a major factor in determining species’ ability to expand their ranges and persist in novel environments. Whether and how invasion occurs in new habitats depending upon the relative performance of populations in different microsites over time is poorly understood. Though largely restricted to disturbed edge microhabitats in its home range, the invasive herb garlic mustard (Alliaria petiolata) invades intact forest understories – a novel microhabitat type – in its introduced range where it is known to impact above and below ground forest understory community composition. In this study, we conducted field surveys in 2003-2006 (sampling period 1) and 2015-2016 (sampling period 2) to evaluate trait variation, biomass allocation, and long-term population demographics and dynamics of A. petiolata growing in three microhabitats. Our results show that adult plants in the edge were significantly taller and branchier, produced more fruits, and had higher total and reproductive biomass than plants in the intermediate and forest microhabitats. Seedling density was highest in the edge microhabitat compared to the forest and intermediate microhabitats, which had similar densities, during both sampling periods. Reproductive adult densities were similar between all microhabitat types in sampling period 1. In sampling period 2, all microhabitats showed a decline in the number of adult plants they supported. The intermediate microhabitats showed the steepest decline, but still supported more adult plants than the forest microhabitat. Population growth rates (lambda; λ) calculated from sampling period 1 showed that the edge, intermediate, and forest populations were increasing (λ>1). Growth rates calculated from sampling period 2 showed a steep decline in the forest understory populations (λ<1). The edge and intermediate populations still indicated growing populations (λ>1), though edge lambdas were lower than in sampling period 1. Overall, our results do not indicate that - at our study site - A. petiolata populations will decline in the edge or intermediate microhabitats in the coming years. Since edge - and intermediate - patches had higher densities of adult plants which produced the most fruit and had the largest reproductive biomass, we speculate that the edge populations, and possibly the intermediate populations, may be helping to sustain the forest populations possibly through source sink population dynamics.

• Research Category: Physiological Ecology, Population Dynamics, and Species Interactions
  Invasive Plants, Pests & Pathogens
  Conservation and Management