New Harvard Forest Publication: Spread and Distribution of Two Invasive Species

Spread and Distribution of Two Invasive Species across Southern New England

Forest ecologist David Orwig along with collaborators Evan Preisser (University of Rhode Island), Alexandra Lodge (Summer 2005 Summer Research Program student- Kenyon College), and Joe Elkinton (Umass, Amherst) report on the spread and distribution of 2 invasive species (hemlock woolly adelgid-HWA and elongate hemlock scale-EHS) across southern New England. This paper is a follow-up study that resampled 142 eastern hemlock stands originally sampled in the late 1990s (CT stands) or 2002-2004 (MA stands). The number of HWA-infested stands increased but the per-stand HWA density substantially decreased. In contrast, EHS distribution and density increased dramatically since 1997-98. Hemlock mortality was much more strongly related to HWA density than EHS density, and many stands remained relatively healthy despite an overall increase in hemlock mortality. There was a positive correlation between HWA and EHS densities in stands with low mean HWA densities, suggesting the potential for host-plant-mediated facilitation of EHS by HWA. Results suggest that interactions between invasive species may not have outcomes similar to those interactions occurring between native-native or invasive-native species pairs.

Preisser, E.L, A. G. Lodge, D. A. Orwig and J. S. Elkinton. 2008. Range expansion and population dynamics of co-occurring invasive herbivores. Biol Invasions 10:201–213