- Pontius, Jennifer
USDA Forest Service, University of Vermont
- Martin, Mary
University of New Hampshire
Forest health in the northeast is of increasing concern due to climate change and anthropogenic pressures. In order to monitor canopy condition across the region, this study uses remote sensing images, which can be used to assess the crown condition of forests over long time periods and large areas. A forest health rating based on canopy “greenness,” photosynthetic capacity, canopy density and water content was applied to Landsat TM5 satellite imagery to quantify yearly forest health from 1984 to 2009, as well as changes and trends in health over that time period.
Initial results indicate that forest condition varies from year to year, primarily due to drought and insect outbreaks, but that the condition of forested ecosystems across the region as a whole has remained relatively stable over the past 25 years. This is likely due to the natural resilience of northeastern forests and their rapid recovery, regrowth and ingrowth following small scale disturbances.
While these results emphasize the natural resiliency of northeastern forests in terms of overall canopy productivity, it is not able to identify changes in species composition or stand structural characteristics. It is therefore possible that species declines have occurred, but ingrowth of competing species maintains canopy condition as characterized by the health index.
In spite of this overall resiliency, there are spatial patterns where decline trends are evident. This highlights the sensitivity of upper elevational forests in the region where low soil nutrient availability, climate extremes and sensitive species converge. Possible causes of long-term decline at these locations include the interacting effects of acid deposition, injury from extreme climate events (winter injury, late frost, ice storms, etc.) and a lack of secondary species to rapidly fill gaps created by mortality and decline.