Page 16 - Tree Line - North Carolina Forestry Association - Fourth Quarter 2021

PART 2
Restoring
Giants:
Eastern and
Carolina Hemlocks
BY FRED P. HAIN,
PROFESSOR EMERITUS & DIRECTOR OF FOREST RESTORATION ALLIANCE,
NC STATE UNIVERSITY
(Fig. 1) Hemlock woolly adelgid. All life stages are found under the white masses.
This is part 2 of a two-part series. The last issue of TreeLine reported on efforts to save American chestnut trees.
Exotic invasive pests are a reality of today’s global economy and travel. Perhaps
because forests are perennial, making it easier for pests to become established, forests have been hit harder than most plant ecosystems. Emerald ash borer, balsam woolly adelgid, Asian longhorned beetle, sudden oak death, laurel wilt disease, and the hemlock woolly adelgid are just a short list of the exotic pests that are threatening North Carolina’s forests.
HWA was first detected in
North Carolina in 1995, and
is now found from northern Georgia to coastal Maine and southwestern Nova Scotia. The insect affects over 90% of the eastern hemlock range. As with most exotic pests, little natural control or host resistance has evolved, rendering eastern hemlocks extremely susceptible. HWA infests both eastern and Carolina hemlock, the only native species in North Carolina. HWA feeds at the base of the hemlock needles (Figure 1), disrupting nutrient flow and browning the needles. Tree death occurs after a few years of continuous feeding. The amount of mortality varies by region,
but in the South, many hemlock
stands have been eliminated.
Hemlocks in the mountains of North Carolina
(Figure 2) are a long-lived species that can reach 800 years in age. They are a shade-tolerant species often found at the edge of streams, where they regulate stream and forest floor temperatures, an important ecological role that cannot be easily replaced by any other tree species. The loss of hemlocks will have profound impacts on forest succession and long-term forest dynamics.
The initial research on controlling HWA focused on traditional insecticides and biological control. There
14 ncforestry.org / FOURTH QUARTER 2021
In the last issue of
TreeLine (Volume 3/Issue 3),
we discussed the research
of The American Chestnut
Foundation in developing an
American chestnut resistant to the chestnut blight. The foundation’s work has resulted in trees that show promise for restoring this once dominant tree of the Appalachian Mountains, and has provided a blueprint for research and restoration of other tree species decimated by an exotic pest.
The Hemlock woolly adelgid (HWA) was first introduced into Richmond, VA from Japan in 1951. By the time it was recognized as a problem, it had made its way into contiguous hemlock stands of the Appalachian Mountains and rapidly spread north.
(Fig. 2) A healthy hemlock along the Blue Ridge Parkway.
FRED HAIN