You are here

Harvard Forest >

Harvard Forest REU Symposium Abstract 2009

  • Title: Stratified Dispersion: Tracking Long-distance Wind and Insect Dispersal Events in the Forest Understory
  • Author: Jenna L Turner (University of Rhode Island)
  • Abstract:

    Understanding the dispersal mechanisms of invasive species is the key to predicting the speed and potential of their spread. Most propagules disperse short distances. However, secondary dispersal mechanisms can transport propagules great distances and such events are the primary determinants of spread rates. The hemlock Woolly Adelgid (Adelges tsugae), is rapidly infesting and killing Eastern Hemlock populations across the Northeastern United States. A. tsugae is a passively-dispersed organism known to be dispersed by multiple short- and long-distance vectors, namely wind, birds, deer, and humans. However, it is nearly impossible to determine the source population of dispersing A. tsugae and therefore to understand its true dispersal dynamics. To circumvent the problems associated with observing dispersal of A. tsugae, we instead tracked dispersal of fluorescent powders which, also consisting of small, passively-dispersed particles, should serve as a proxy to A. tsugae dispersal. By dusting individual hemlocks with different colored powders, we were able to define “source” populations, control propagule pressure by manipulating the amount of powder applied to each tree, and to determine with confidence its dispersal through the forest understory. We tracked movement of the fluorescent particles using sticky cards located from 10 to 400 m away from the source trees. The amount of powder captured was quantified by photographing cards under a black light and by counting the number of fluorescing pixels using image analysis software. We captured powder at a distance of 400 meters, with many of the longest dispersal events being associated with transport of powder by insects. This suggests that wind alone may not explain the movement of A. tsugae between trees within forests and that a secondary dispersal mechanism such as insects may facilitate longer-distance dispersal events. Future work could consider whether insects are truly capable of dispersing A. tsugae.

  • Research Category: Invasive Plants, Pests & Pathogens