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Harvard Forest REU Symposium Abstract 2005
- Title: Hemlock Woolly Adelgid Range Expansion:Field Survey vs. Limited Range Protocol
- Author: Phil J Lebranche (Holyoke Community College)
- Abstract:
The study of range expansion is a critical part of invasive species research. Harvard Forest, as a long term ecological research site (LTER) in the path of hemlock woolly adelgid (HWA) expanding range, offers an unique opportunity. An REU intern surveyed Harvard Forest tracts during 2004 and again in 2005 to monitor changes in HWA infestation. Furthermore, previous research (Costa and Baribault, unpublished data) suggested that dispersal of HWA crawlers was inversely density dependent at low population densities, which might facilitate range expansion. The overall population of HWA in Harvard Forest tracts was slightly lower in 2005 (0.54%) compared to 2004 (1.85%) indicating no growth in range; the number of infested trees were (41) and (12), respectively. While 5 tracts were previously found to be infested only 3 were noted in the current year. The relative precision at such low densities makes it difficult to ascertain the significance of the differences noted. A limited range protocol (LRP) was developed to assess the number of infested trees and associated HWA densities within 27 yards of the first infested tree found within a stand. Stands with a wide range of infestation levels were selected. At low HWA density, the proportion of infested trees relative to HWA population counts was inversely density dependent, and there was no density dependence at high population levels. These results lend support to the hypothesis that increased crawler dispersal at low densities may drive range expansion.
- Research Category:
