By late 2012, forest health monitors in western New York and Pennsylvania knew that they were about to experience a severe outbreak of the non-native Gypsy Moth. Surveys showed an unusually high density of egg masses on the branches and trunks of trees, but neither egg densities, nor the distribution of primary host trees are ever perfectly known across the forest, so translating general predictions to a map remains a challenge. Using the best information available, forest managers prioritized their lands for spraying, then they watched this event unfold.
Over the last 15 years, Mountain Pine Beetles have killed large tracks of ponderosa pine across the Black Hills of South Dakota. Beetles thrive with continuous stands of dense trees, and decades of fire exclusion have led to that landscape and stand-level condition. That favorable habitat may help explain why the current epidemic of this native insect has been so severe. In this summer 2010 aerial photograph, the patchy structure of recent and older tree mortality shows up well around Harney Peak--the highest elevation in the Black Hills.
Spring often brings defoliating insects to the forests of Louisiana. In this image from early May 2010, defoliations from forest tent caterpillars and baldcypress leafrollers create an erupting "measles-like" pattern. Note the subtle differences in severity outward from the centers of several of the blotches. The insets show the baldcypress leafroller (left: photo by Gerald Lenhard, LSU: bugwood.com 0014219) and the forest tent caterpillar (right; photo by Stephen Katovich, USFS; bugwood.com 1398248).
Outbreaks of the defoliating pine butterfly are rare. In eastern Oregon, outbreaks occurred in 1908-11, 1940-43, 1982 and from 2008 to 2011. Sometimes defoliations can lead to mass mortality of ponderosa pine—the primary host, but not always. This current outbreak on the Malheur National Forest is largely responsible for the forest change anomalies in ForWarn for September 29, 2011 compared to 2010. According to aerial detection surveys, areas inside and outside these pine butterfly areas were also affected by spruce budworm.
This fall 2011 webworm outbreak in the Hickory Creek Wilderness Area of the Allegheny National Forest, Pennsylvania stands out against the near normal (blue) background that dominated the state in early fall. There were minimal indications of defoliation in mid-August, but clear patterns of severity were clear by mid-September. This anomaly persisted through November, when leaflessness is the normal pre-winter condition for deciduous trees.
A sizable portion of the Wenatchee National Forest, Washington shows less vegetational vigor than it did at its peak of the last decade. While such declines in NDVI often result from tree death due to wildfires in the west, no large fire has occurred here as is shown by the distribution of MODIS hotspots (shown as white triangles) between 2000 and 2011. Much of this reduction through September 13, 2011 may have been caused by the cumulative effects of defoliating insects on tree mortality, particularly from spruce budworm.
This image shows forest change anomalies on the north slope of the Wasatch Range of Utah on September 13, 2011 compared to the prior year. The high elevation zone above treeline is shown as an uncolored area under the words “Wasatch Range”. Most of the region’s forest is blue, meaning it is similar to that of 2010. Just below treeline, the Range’s slopes show a moderate to extreme departure in greenness. In recent years, the north slope in particular, has experienced repeated outbreaks of the Mountain Pine Beetle according to aerial surveys, but these were usually at a lower elevation.
According to climate data, coastal North and South Carolina were having a mild drought in mid May of 2011. Mean water flow for the Pee Dee River near Pee Dee, SC during the 24-days prior to May 16 was 15.9% below the 2003-2010 average for that time according to USGS statistics (http://waterdata.usgs.gov). These clues suggest that this reduction along the Waccama and Pee Dee Rivers of the Carolinas is not the result of flooding.