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.

EFETAC's ROLE: This project is supported by EFETAC funding.

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 was 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. 

Core data have been cross-dated, and relationships between foliar symptoms and decreased increment growth and site variables have been quantified. The increment data indicate that there is a threshold in crown symptom development after which a hemlock tree will begin to decline in increment growth. Using this threshold in logistic analysis, preliminary results indicate three site parameters as significant in classifying hemlock sites into those that would have declining trees in an HWA infested area and those that would not. The parameters are January minimum temperature (average), slope, and hill-shade (a measure of radiation exposure). The analytical approach is currently under review. Once analysis is completed, the results can be used to create a GIS map for the Northeast that will indicated the probability of hemlock decline across the region.

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, jennifer.pontuis@uvm.edu, or (802) 656-3091
• William Livingston, University of Maine School of Forest Resources, WilliamL@maine.edu or (207) 581-2990

Updated September 2010