PARTNERS: University of Maine School of Forest Resources, USDA Forest Service Northern Research Station

SUMMARY: Land managers need to effectively mitigate the potential stress complex of Hemlock Woolly Adelgid (HWA) and drought currently facing hemlock in the northeastern United States. The development of comprehensive landscape-scale, spatially continuous models of the hemlock resource and its susceptibility to HWA and drought stressors would greatly aid this goal. Multidiscipline research for this project, which began in May 2007, has the objectives of (1) developing field based models to predict the impacts of drought and HWA infestation on hemlock decline; (2) translating field based models to a landscape scale using GIS layers; (3) assessing the accuracy of the models by independent validation using new sample plots; and (4) disseminating information on methods and the potential of such approaches to other researchers, land managers, and GIS specialists.

STATUS: Ongoing

PROGRESS: Over 1100 cores were collected from 574 hemlock on 42 HWA infested sites in PA (3 sites), NY (22), NJ (3), CT (12), and MA (2) in 2007. Another 98 cores from 49 hemlock on 7 noninfested sites in ME (2) and NH (5) were sampled in 2007 which can be added to an existing database of 36 noninfested sites sampled in ME in 2006. The same number of cores from non-hemlock trees were sampled on all sites to examine how hemlock responds to stress differently from its cohorts. Increment measurements have been completed on all hemlock cores and half of the non-hemlock cores from 2007. Cross-dating is currently in progress.

Trends in increment growth can be related to data currently available from these sites, including: site (aspect, slope, landscape position, curvature), soil (drainage class, texture, depth to restrictive layer, depth of organic, cation chemistry, pH, percent coarse fragments, maximum rooting depth), stand (percent hemlock, percent mortality, size class), HWA infestation levels, and climate (drought history, minimum and average temperatures) variables. To better model site factors associated with hemlock decline in northern New England, 15 additional sites were sampled during 2008 in the northern part of the insect’s infested area, central MA, where HWA incited decline is occurring. 

Over the coming fall and winter, core data will be used to identify current and previous increment declines in tree chronologies, relationships between foliar symptoms and decreased increment growth, and quantification of how site variables vary with decline in increment growth. These field based models will serve as the basis for developing GIS layers showing sites having characteristics associated with previous declines in hemlock increment.

LINKS:

University of Maine School of Forest Resources

USDA Forest Service Northern Research Station

CONTACT:

• Jennifer Pontius, Northern Research Station Research Ecologist, jpontius@fs.fed.us or (603) 868-7739 
• William Livingston, University of Maine School of Forest Resources, WilliamL@maine.edu or (207) 581-2990