Page 18 - Tree Line - North Carolina Forestry Association - Fourth Quarter 2021

Following clonal propagation of these individuals, several studies were done, including a seven-state study of planted resistant and susceptible hemlocks. After four years, the plots were surveyed and 96% of HWA-resistant hemlocks survived, compared to 48% of susceptible trees. The surviving HWA-resistant trees were taller, with more lateral growth. These preliminary results suggested that, while sparse, HWA resistance may exist in native hemlocks.
The Forest Restoration Alliance (FRA) at North Carolina State University has also started to search
for HWA resistance in the southern range of eastern hemlock and Carolina hemlock. FRA has found and propagated for screening native hemlock genotypes with putative HWA-resistance. FRA is also working to develop hybrid hemlocks crossed with resistant Asian hemlocks. The greatest success to date has been the crossing of selected Asian species with Carolina hemlock, but work continues with both native species. Facilities for propagating clonal hemlocks (Figures 3 and 4), hybridizing with resistant species, and screening for HWA-resistance have been set up at the Mountain Research Station in Waynesville, NC. HRI funded this unique facility, which is dedicated
to hosting resistance screening and is an example
of the FRA/HRI partnership (Figure 5). Testing for resistance by exposing the various hemlocks, both native and hybrids, is ongoing (Figure 6). Meanwhile, the Linville River Nursery of the NC Forest Service is
already producing hemlock seedlings for restoration. While the current seedlings are not HWA-resistant, the nursery is gaining the experience needed for seedling production when HWA-resistant seed and clones are available.
In combating exotic invasive pests, scientists and foresters can look to The American Chestnut Foundation, the Hemlock Restoration Initiative, and the Forest Restoration Alliance for guidance on establishing a forest-pest management framework.
( Fig. 6)
Infesting hemlocks with HWA in a resistance screening study. The screening room has temperature and light controlled.
16 ncforestry.org / FOURTH QUARTER 2021
BEN SMITH