Landscapes Forest and Global Change - ESA - Escola Superior ...

K. L. Martin & P.C. Goebel 2010. Impact of hemlock decline on successional pathways and ecosystem function
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move westward in Pennsylvania (Figure 1). HWA feeds on the parenchyma cells of xylem rays,
which causes the death of branches and leads to mortality in T. canadensis (McClure 1991).
There is no evidence that T. canadensis or T. caroliniana Engelm., a species endemic to the
southern Appalachians, have any resistance to HWA. Thus complete mortality occurs in 4-15
years (McClure 1991; Orwig and Foster 1998). Evans and Gregorie (2007) estimate HWA to
spread at a mean rate of 12 km yr -1 , but both the spread and effects are accelerated in southern,
warmer portions of the range (Ford and Vose 2007).
On-going T. canadensis mortality is undoubtedly altering forest dynamics including species
composition, diversity, and nutrient and energy exchanges. T. canadensis forms a foundation
that supports unique species assemblages, including cold-water fishes, birds, and
macroinvertebrates (Ellison et al. 2005). Across the T. canadensis range, pollen records
following an historic population decline 5,000 ybp provide useful insight into species likely to
respond to hemlock mortality, including Betula, Acer and Quercus species (Heard and Valente
2009). However, communities that develop following T. canadensis mortality may be regionspecific,
thus creating greater dissimilarity across portions of the landscape once dominated by
hemlock (Ellison et al. 2005; Orwig et al. 2008). Much of the current understanding of the
impact of T. canadensis mortality is centered in the Northern Hardwoods forest province. Yet, a
large portion of the T. canadensis range lies within the Central Hardwoods forest, a province
extending from West Virginia to Alabama and west to Missouri and Wisconsin (Fralish 2000).
We are working to clarify the contemporary impact of this introduced disturbance across the
central Appalachians. The objective of our on-going study is to quantify changes in plant
community structure and ecosystem function in headwater stream riparian forests of the central
Appalachian Mountains. For the broader study, we are using a chronosequence of time since
HWA invasion to examine the following questions:
1. How will or does T. canadensis mortality impact headwater streams at local scales, moving
from the stream bank upslope
2. How much variation can we expect in these changes both across the central Appalachians
3. How do our results compare to understanding from the northeastern U.S. and southern
Appalachian Mountains
4. What can we predict in terms of forest composition and function over time as T. canadensis
mortality progresses and forests transition to an alternate ecosystem
Before HWA arrives, we are quantifying the vegetation and environmental relationships in T.
canadensis dominated ravines important for natural heritage and recreation on the unglaciated
Allegheny Plateau of southeastern Ohio. Therefore, in this paper we focus on our first question:
How will or does T. canadensis mortality impact headwater streams at local scales, moving
from the stream bank upslope According to the projected rate of spread (12 km -1 year, Evans
and Gregorie 2007) and the current USDA Forest Service map of HWA invasion (Figure 1),
Ohio may be invaded within the next few years.
2. Methodology
For the broader study, areas have been identified in the central Appalachian region, including
sites within the Allegheny Mountains of Virginia and West Virginia, and the Allegheny Plateau
region of eastern Ohio. Using the United States Department of Agriculture (USDA) Forest
Service HWA distribution map and information available from local land managers, we have
identified and acquired research permits for study areas in the states of:
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.