PARTNERS: USDA Forest Service Southern Research Station, USDA Forest Service Region 8, USDA Forest Service Northeastern Area State and Private Forestry

SUMMARY: In the southern Appalachians, eastern (Tsuga canadensis) and Carolina (Tsuga caroliniana) hemlock can be significant components of stream riparian zones, serving multiple functions for streams. To the north, in New England, eastern hemlock form whole stands that can influence streams directly or indirectly through watershed processes. Loss of hemlock species due to hemlock woolly adelgid (HWA; Adelges tsugae) is likely to have impacts on streams through several causal pathways, including changes to stream shading and temperature, allochthonous input and food webs, large wood recruitment and physical habitat, and alteration of hydrologic and nutrient cycles. Of particular concern are impacts on coldwater fish species like native brook trout. Most assessments to date have been qualitative or focused on a single pathway. Research on some of these impacts is underway, but studies are incomplete and few are published. Other impacts can be inferred from knowledge about ecosystem structure and function.

STATUS: Ongoing

PROGRESS: When data are incomplete, Bayesian belief networks (BBN) can be used to combine available data with expert knowledge to integrate multiple pathways and assess their relative influence. BBNs have characteristics of directed graphs and probability theory. BBN models are being developed to synthesize what is known about possible effects of HWA on streams throughout the range of hemlocks in the eastern United States. Several prototype models have been developed and presented to professionals. Models at tree, stream segment, and watershed scales are also currently under development.

LINKS:

USDA Forest Service Southern Research Station

USDA Forest Service Region 8

USDA Forest Service Northeastern Area State and Private Forestry

CONTACT: Patricia Flebbe, Southern Research Station Research Biologist, pflebbe@fs.fed.us or (540) 231-7202