HEMS (the Hemlock Ecosystem Management Study) is a multi-year study of how loss of eastern hemlock trees affects ecosystems and people in Maine.  Mature hemlock trees that create unique aesthetic and environmental conditions in the forests they dominate face infestation by the expanding range of the hemlock woolly adelgid (HWA). Once this invasive aphid-like insect infested hemlock trees south of Maine, they nearly all died within 10 years.  The range of the invasive HWA is expanding northward; it has arrived in southern Maine.

Pre-emptive logging is one management option that some woodland owners are considering before losing hemlock trees to HWA. Cutting most hemlock trees would have major socioeconomic and ecological consequences in Maine, as would doing nothing to infested forests. By understanding these consequences, HEMS can help land managers make informed decisions.

The HEMS team uses experimental treatments in the field to measure effects of logging and of trees dying slowly, such as increased light levels, soil compaction, and woody debris accumulation.  The team investigates how plant and animal biodiversity change in response to these variables.  This research helps land managers understand what kind of forest to expect after hemlock forest disturbances.   Perceptions of scenic quality and other non-consumptive forest values are assessed, along with values of logging hemlock trees. Remote sensing and GIS (Geographic Information Systems) are used to map the distribution of hemlock-dominant stands across Maine.  This research helps agencies/organizations that are detecting the spread of HWA and planning what to do with public or preserved lands that may become infested

In the summer of 2012, hemlock in selected plots were girdled around the tree, leaving a strip of cambium to allow for partial nutrient flow.  This mimics the slow death of a HWA infested tree.  Trees were then checked for dieback in the summer of 2013 and hemispherical canopy photos such as the one on the right were taken to calculate the difference of solar radiation coming through the canopy before and after girdling.