Vegetation Research & Projects: January, 2009
Control and study of Hemlock Woolly Adelgid: protecting hemlocks using biological & chemical controls
- Beetles: Foresters released hundreds of predatory beetles, Laricobius nigrinus, near Cosby Knob shelter (10/29/2008) and along the Little Cataloochee River (11/06/2008) as part of coordinated efforts to save hemlock stands in the park. These beetles are native to the Northwest United States where they feed on native adelgids. Raised in a University of Tennessee lab, about 300 at a time are released to coincide with the Hemlock Woolly Adelgid emergence (when the young adelgids are “fat and juicy,” as one park forester put it). Since the project began, 350,000 biocontrol beetles (two species) have been released. It may be too early to know whether this program is working. Results from monitoring show we cannot predict which treated hemlocks will survive.
- Pesticides: Foliar (needle) spraying of hemlocks began in early November. This will continue through the winter and spring and target hemlocks growing along roads, in campgrounds, near the visitor centers, and in picnic areas, where falling trees could be an especial hazard to visitors.
Do these controls work? According to vegetation reports based on monitoring of treated sites, “results of biocontrol treatments are still in their infancy and have been mixed. Some locations show hemlocks are holding on while trees in other locations have declined severely or died. Survival may be the result of site, microclimate or other factors. Long term monitoring will reveal a clearer trend.” Look for more information in an upcoming “Dispatches.”
Balsam Woolly Adelgid (BWA) impacts on Fraser firs and forest insects
- Monitoring in the Park shows scientists a discouraging trend
Non-native balsam woolly adelgid (Adelges piceae) on Fraser firs are increasing. Densities of adelgids on Fraser fir trees were nearly 10 times higher at all four mountaintop monitor sites in 2008 than they were in 2007.
In another study, Park foresters collaborated with emeritus Mississippi State cone insect specialist Dr. Evan Nebaker to collect cones from five fir tree study areas. Dr. Nebaker will document all of the insects he finds living or laying eggs within the cones, to shed light on the microhabitats (small homes) that the cones provide. It is important that we know what lives in these cones because BWA has killed 90 percent of the firs in the park since it first appeared in the 1960s, and until we find out why some firs are resistant to BWA, continued loss of the trees threatens the insect species that use the fir for food, shelter, and a place to rear their young.
NPS partner researchers monitor high elevation beech gaps in Spruce-Fir forests such as this one along the Appalachian Trail near Icewater Spring Shelter.
Beech scale and Beech gap studies
Ashley Morris, a geneticist who completed her doctoral study in beech gap genetics in the Park, found one in ten of her study sites consisted of beech clones. While this is one way beech normally reproduce, it means that “the root sprouts, which are genetically identical to parents killed by the disease, will also be impacted by the disease as they mature. Foresters think that natural resistance to the disease is low.
In New England, studies by David Houston during the 1980s revealed 1 percent resistance to beech bark disease. No treatment for the disease is known. Some of the Park’s monitoring plots have individual mature beech still in healthy condition above a thick understory of beech sprouts. Houston reported that in New England remaining overstory beech that survived a wave of beech bark disease were resistant to the scale. Whether this becomes the case in Great Smoky Mountains National Park is the subject of future monitoring and research.
- Monitoring beech over time
Ten monitoring plots were established in 1994. Scientists return to them every other year to see how many trees survive, to measure the density of the scales on the trees and check for Nectria fungus, and finally to assess tree health by noting dying branches, leaf loss, and growth of shrubs that crowd out the beech.
Scientists are still analyzing data from the 2008 season. Past monitoring has shown high mortality rates of mature beech in the monitoring plots, and dense blackberry growth in the new sunny areas. Foresters have also seen beech root sprout reproduction around dead “parent” trees, which means that young beech are returning.
Monitoring Butternut tree health
In 2008, researchers returned to butternut tree monitoring sites. Since 2005, four of 47 butternuts had died from cankers, and others perished from wind and ice storms. By noting which trees survive, scientists have been able to make some conclusions about characteristics that survivor trees have. Survivors tend to be mature, receive full sun so their branches keep growing, and have tightly healed cankers (often almost invisible). Doomed trees include smaller butternuts that grow in the shady understory, have open cankers with decay, and have “structural weakness” (weak or broken branches, or rotting) that would not stand up to a strong wind or ice storm. Because the trees seem to reproduce successfully only in the sun, most of the new growth is along road edges. Scientists noticed that the “cyclical nut production” happened this year as usual, but no one knows how many of those seeds will sprout and survive.
A Purdue University forest geneticist has applied for a research permit, in coordination with the U.S. Department of Agriculture, to collect butternuts and study how genetically diverse they are. Having a limited number of survivors means that only a very small amount of genetic material is being passed on. Reduced genetic diversity often means reduced ability for the population to adapt when the next disease comes along.
Ridding wetlands of weeds
2008 was the second year of a project to rid wetlands of exotic plant species—such as the multiflora rose—and to plant native plant seed in their place.