Sustainably Managing Beech Bark Disease
The ecological epidemic known as Beech Bark Disease (BBD), is caused by a disease complex consisting of multiple causal agents; first, an exotic scale insect (Cryptococcus Fagisuga), feeds on the sap of American beech (Fagus Grandifolia), creating microscopic holes that allow a pathogenic fungi of the Neonectria genus to penetrate the bark layer and produce its spores, inevitably damaging or killing the tree. Few clusters of American beech (20%) further considerations on harvesting techniques and methodologies must be investigated. Regardless of the previous stand composition, the aim for sustainable forest management will be continuing to maintain a balanced, diverse forest ecosystem during a period of inevitable, major loss of a tree species.
Anticipating the arrival of BBD by decreasing the basal area of mature beech trees, while increasing the distribution of other species (diversification), is a tactic that should be utilized by forest management to reduce the susceptibility of uninfected stands. Other considerations often include selective trimming of beech that have reached the canopy to reduce dominance of the species; focusing on decaying, older trees. As well, guidelines for the BBD have suggested retaining more vigorous beech trees (potentially resilient to BBD, thereby preserving genetically resistant trees) and to focus on the regeneration of shade intolerant species by creating canopy gaps (exceeding 30 feet); allowing these species to outcompete beech in an environment that favours them. In combination with converting the stand composition to something more diverse, utilizing herbicides and aggressive cutting techniques (clear-cutting) have yielded positive results in mitigating prolific beech regeneration. Keys to effective forest management of BBD will be to reduce beech ‘root sprouting’ (dense thickets of beech renewal developing from root structures damaged by harvesting activities), and to replace beech trees with suitable, native alternatives. Red Oak is regarded as an acceptable substitute for American beech trees because of their shared preference of ecological sites and soil composition, as well as their ability to produce nutrient rich seeds (viable alterative for wildlife) and develop large crowns.
As a response to the initial phase of BBD, harvesting all merchantable beech timber is a strategy that has been implemented by the Haliburton Forest Reserve. The risks of optimizing economic returns by process of wholesale liquidation include: destroying irreplaceable wildlife habitat, triggering high rates of beech regeneration, and not adequately considering the likelihood of beech tree survival; failing to do so dismisses a species that may yet have a chance of surviving - approximately 50% of beech in the Adirondacks survived for greater than 28 years, post BBD infection. Instead, management of stands that have already been infested with BBD (advancing or killing front) should seek to retain both mature trees that will inevitably die but can still provide valuable habitat for local wildlife (ecological benefits) and healthy, seemingly unaffected trees that may be genetically resilient to BBD. Besides, attempts to completely eradicate the species have rarely succeeded because of American beech’s unique ability to rapidly produce regenerative sprouts from their root systems.
The importance of American Beech extends well beyond its market price and quantifiable denomination. At least forty bird and mammal species rely on the tree as a food source, nesting location, foraging site or predatory vantage point. The role beechnuts play - as a food source - is especially critical in areas where few, other hard mast species are prevalent (Hickory, Oak) because of the lack of food alternatives. Further, the cycle of BBD; initially attacking mature, large, beech trees is problematic to future seed production; the average beech tree takes at least forty years to develop before it can produce seeds. As a result, if the disease continues to affect successive generations, remaining beech trees will no longer be able to produce seeds; a vital component of some species’ diets. Similarly, the most at risk beech trees (older, decaying) are the most valuable to nesting arthropods, mammals and birds.
The effect of a non-native pathogen on a native species and the subsequent impact on wildlife is difficult to determine because of the many other factors that will contribute to the outcome of the forest ecosystem. How populations that rely on beech will respond to such dramatic, sudden changes (relatively speaking) is largely theoretical and will only be conclusive after BBD has devastated the forest ecosystem or more relevant data is collected. However, by including conservation-based guidelines in forest management plans, we are more likely to succeed in maintaining species’ populations and overall forest diversity. The difficulty of removing beech trees from their natural environment lies in their ability to develop in well-shaded areas and more uniquely, their capacity to rapidly produce root sprouts (regeneration), when triggered by stresses - such as harvesting, extreme weather, and exposure to sunlight. BBD alone can elicit root-sprouting behaviour by harming the integrity of the tree and by inducing defoliation or causing mortality. As well, by harvesting beech in an attempt to eradicate BBD, human intervention may trigger an aggressive resurgence of beech thickets that will inevitably out-compete other young seedlings, including birch, hemlock, maples and other understory vegetation. Continuous sprouting (as a result of BBD) has been theorized to create an eventual monoculture of American beech. As well, the successive, deformed seedlings of the beech population (post infection) that are already infected with the disease will be killed by BBD before the tree can reach maturity. This ability to sprout rapidly often leads to an overall increase of beech density in a forest. The end result is a less healthy, lower valued forest with much less diversity than the previous stand. In an attempt to combat sprout intensity, a number of harvesting techniques have been tested to control successive beech populations. The findings revealed that seasonality of harvest (winter or summer cuts), treatment methodology, and reducing the density of canopy did not greatly impact the total number of sprouts. However, the data did demonstrate that significant sprouts are produced around resilient trees with greater vigor (potentially nine times greater than other beech trees); so, theoretically cultivating these genetically diverse trees, would result in the beginning of a BBD immune population. In conclusion, the emergence of Beech Bark Disease (BBD) has jeopardized the longevity and health of an overwhelming majority of all American beech species.
In order to sustain hardwood forest diversity and preserve wildlife populations that have relied on the ecological value of beech trees, future research must continue to investigate beech trees resilient to BBD. Further, by including conservation-based guidelines in forest management plans we will avoid attempts to eradicate an entire species by wholesale liquidation, which would ultimately harm a larger number of wildlife species and eliminate the 1% of resilient beech trees. Lastly, continuing to study control techniques to mitigate aggressive beech sprouting will further assist with these goals.
