Above: Evidence of hemlock wooly adelgid. Photo by Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station / © Bugwood.org / CC-BY-3.0-US.
By Ryan Trapani
Each hunting season there is a certain amount of deer that must be harvested in order to last me through the year. Normally I first hunt those areas that are both accessible and abundant in deer. These conditions are usually met in the larger, more fertile valleys where a diversity of food and cover sources is available for wildlife. Fortunately, minimum deer harvest quotas were met early on and allowed for more time to be allocated towards hunting inaccessible areas in the mountains. Hunting these areas offers another type of hunting experience. Deer behavior and physiology can differ significantly when hunting pressure is low. Sitting in a tree-stand far away from the familiar sounds of human dwelling, the forest and its inhabitants become the focus.
Still, I could not help but notice our society’s culture reflected in our forest one quiet morning sitting 30 feet up a tree. Sometimes, it literally hits you right in the face. A branch is what hit me in the face! Its needles were short, flat and soft. It was a hemlock. I chose this spot because its dark, evergreen boughs provided excellent background cover, helping to blend my human silhouette among the forest. The stream nearby and its occupants also benefited from the hemlock’s cover since cooler water can hold more oxygen creating better conditions for fish and the prey they depend upon.
Unfortunately, this branch did not hold promise for the future in preserving the aforementioned benefits. It was riddled with a white, cotton-like substance along the branch and needles. I knew all too well what it was and how it got there. It was hemlock woolly adelgid (HWA).
Our thirst for cheap manufactured products with China can now be reflected on a branch of a tree high up in the mountains, whether on steep rocky bluffs or deep down in ravines. Hemlock woolly adelgid (Adelges tsugae) is a relative of aphids. It literally sucks the life out of trees through the needles. Hemlocks usually succumb to HWA within 2 – 8 years. The crown will begin to recede and appear less full. HWA was accidentally introduced from Asia in 1951 by nursery stock. It began causing noticeable damage by the 1980s and is in the forest of 17 eastern US states. Its main source of food is the eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana). Carolina hemlock is mostly isolated to the Blue Ridge Mountains of the Carolinas and Virginia. Eastern hemlock is found locally in New York State and throughout most of the eastern US. In Asia, the HWA does not cause any significant damage since it is balanced by adequate predators and the hemlocks there are able to tolerate their presence.
In a forest setting, there currently is no control for HWA. In a landscape setting, homeowners have the option of applying pesticides to the soil surrounding specific trees. Applications of pesticides should always follow the label as instructed. They usually have to be re-applied too. Landscape applications are not feasible in a forest setting due to expense and lack of study pertaining to their success. Instead, the USDA National Arboretum began a breeding program in the 1990s. Search parties were sent over to Asia to gain research and bring back seed sources of Asian hemlocks resistant to the HWA. Fortunately, researchers have been able to hybridize one of North America’s hemlocks (Carolina hemlock) with Chinese hemlock (Tsuga chinensis). They have developed some hybrids that are showing some resistance to HWA. More research needs to be conducted before hybrids are offered to the public for restocking.
The threat to our forest from such insects and diseases as HWA is a product of our trade with far and away places. It may also have to do with the fact that North & South America were separated from Europe, Asia, and Africa for millions of years creating flora and fauna of the former more at risk from the latter. Many exotic species have found a niche in our forest, and it often is impossible to eradicate or control them. The future may hold promise in programs similar to the hemlock hybridization programs that link resistant genes of Chinese seed sources with North American seed sources. The American Chestnut Foundation has also gained success in a similar hybridization program involving American and Chinese chestnut and is now distributing them on a contractual basis. We’ll have to see how it goes.
On another more positive note – the HWA does seem to be slowing down in some areas throughout the Catskills in recent years – few experts understand the reasons. However, I have noticed hemlock regenerating heavily in some areas – reclaiming forests that were once used by the tanning industry in times past. In other areas, hemlocks have been usurped by faster growing trees that regenerated after heavy cutting and/or farm abandonment. In the future, hemlocks may once again regenerate these stands since few trees can germinate and establish underneath the shade of mature trees. There is no doubt that both the tanning industry and the recent HWA have impacted the eastern hemlock tree. However, there are other factors effecting hemlock that should be considered. Similar to some other trees – hemlocks are also susceptible to deer browse especially during winter. Deer use mature hemlock stands as wintering yards for shelter from cold winds and deeper snow depths. These areas can contain extremely concentrated numbers of deer for long periods of time where browsing of tree seedlings can be extreme – including hemlock. The HWA may be a problem that cannot be solved, but the deer issue can be – it’s a matter of sunlight. The deer are hungry and their impacts upon our forests are growing each year. Deer have always relied upon the forest as a food source. What has changed is the quality of this forest. Humans in the past have relied upon deer for a source of food, clothing, and tools. Ironically deer too have relied upon humans to provide sunlight into the forest (mostly through burning in the past) in order to provide a diversity of forest types – age classes; species composition; and size classes. Our forests today are mostly even aged and maturing – offering little in the understory for a growing deer herd. Hemlock – like oak, cherry, walnut, and hickory are finding it more difficult to make a living in the younger age classes without the forest’s chief herbivore being satisfied – the white-tailed deer. If you would like to know more about how to provide better quality wildlife habitat, call CFA. www.catskillforest.org
From the Forest articles are written by staff at the Catskill Forest Association, a Watershed Post advertiser.
