New maps show just how bad gypsy moth invasion was

Maps make use of satellite imagery

Map compiled by UMass postgraduate fellow Valerie Pasquerella shows the vastness of defoliation from gypsy moth caterpillars on July 13, 2016. Areas shown in brown have a "high difference" between predicted greenness and actual conditions. Green areas have a low difference.

AMHERST, Mass. (WWLP) – Wide swaths of central and eastern Massachusetts, as well some areas in western Massachusetts saw heavy defoliation from this year’s gypsy moth caterpillar invasion, and some new maps are showing just how bad the problem was. The maps, compiled by UMass postdoctoral fellow Valerie Pasquarella, point out some of the hardest-hit areas in southern New England.

The maps were compiled using images from the Landsat satellite program. While the program itself has existed for decades, its images only became free for public use in 2008.

Previously, Gypsy moth caterpillar damage was generally only tracked through the use of aerial surveys, conducted by numerous pilots flying over affected areas. This time-consuming process was usually only done once per season, whereas new Landsat images come through every 16 days.

In her maps, Pasquarella compared the satellite images to model predictions of how green the vegetation was anticipated to be. A map based on data from July 13, for instance, found that most of western Rhode Island had a large loss of foliage, compared with how “green” the area was expected to be at this time of year. It is a similar story in much of south-central Massachusetts, large pockets of eastern Connecticut, and smaller swaths of eastern and western Massachusetts.

Pasquarella’s work also shows the change in “greenness” over time. As the summer progressed, trees that lost their leaves due to the gypsy moth caterpillars began to grow them back. As an example, she zoomed in on an affected area along Route 6 in eastern Connecticut. While the area was largely showing a “high difference” between projected greenness and actual greenness on July 13, things began to improve by August 14, and by the end of August, there was very little difference between the projections and the reality.

“It’s a straightforward process of subtraction,” Pasquarella said in a UMass news release sent to 22News. “It’s characterizing atypical patterns in forest vegetation condition over large areas, plus tracking through time, which yields near real-time monitoring of disturbance.”

Gypsy moth caterpillars are voracious eaters, and are known to eat the leaves of more than 500 species of trees and shrubs.


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