Beech Bark Disease Can Be Amplified by Harvesting

By Maxwell McCormack

     Recently, I had the opportunity to participate in a small group field session to discuss beech bark disease (BBD) in Maine hardwood stands. It was a good review of earlier coverage on BBD in Maine Woodlands (March and April, 2013) and confirmed that the information there remains pertinent.

       A new concern of mine is that ongoing mechanical, partial harvests are resulting in conditions that foster sprouting of diseased beech (Fagus grandifolia Ehrh.) The sprout thickets are dominating many of our best-quality hardwood sites, displacing desirable species such as sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton).

     A continuing problem is the attendant decreased production of beechnuts. This is singularly significant among Maine’s hard mast crops. The following extracts of text from a 2001 Maine Department of Inland Fisheries and Wildlife document elaborates this point:

     “In seasons of abundant beechnut crops, the nuts are a primary component of the diet of many species, including: black bear, white-tailed deer, squirrels, pine marten, microtine rodents, and ruffed grouse. Maintenance of mature, nut-producing trees in hardwood stands will enhance the survival and reproduction of these species and will benefit species such as pine marten and fisher, which prey on rodents . . . Beech mast exceeds all other mast as a high-octane food for wildlife; therefore, more is best.”

     In travelling to and from the BBD session I had the benefit of riding with David R. Houston, USFS retired pathologist, a recognized specialist on BBD. I received an informative “short course” en route. During the field discussions, we also had the counsel of William Leak, USFS hardwood silviculture specialist; William Ostrofsky retired MFS pathologist; and his successor, Aaron Bergdahl.

     Most foresters and woodland owners are aware that BBD is not a newcomer to our forests. This alien invader entered North America through Halifax, Nova Scotia in the late 19th Century. BBD results when beech bark is infested by the beech scale insect (Cryptococcus fagisuga), and subsequently by bark canker fungi of the genus Neonectria.

     BBD has caused severe damage to American beech in the U.S., west to Wisconsin, and south to North Carolina and Tennessee. Beech is very shade tolerant and, after partial harvests, diseased root systems respond by producing understory thickets of aggressive sprouts that can quickly exclude regeneration of other hardwood species.

     Beech trees have extensive root systems concentrated in surface soils. They are the basis for the sprout thickets that follow disturbances. They are so sensitive that just the scuff of a boot into the soil, especially in the spring, can cause enough injury to stimulate sprouting.

     Immediately after harvesting a stand containing beech trees, the site can appear to be relatively clear and aesthetically desirable, but beneath the soil surface lives a network of roots with the potential to sprout robustly. This condition presents a serious challenge to woodland owners and delays in treatment can be costly.

     The only known, effective treatment is a properly prescribed application of glyphosate herbicide that can be utilized pre-, at-, or post-harvest. After disturbance, the biological clock starts ticking, expressed as the volume and height of sprout biomass. Early foliar treatments are best, as long as there is sufficient leaf surface of target. Knee high is good, waist high OK. From there on up, the odds for success drop off precipitously. The better the site quality, the sooner you need to take action.

     With a long-range eye on the future, I encourage woodland owners to keep an eye out for smooth bark beech trees that exhibit a possible resistance to BBD. Though such trees are rare, they are out there, and sometimes occur in groups. These groups could be clonal, but recent studies indicate that half-sib groups also occur as a result of selective caching procedures carried out by blue jays.

     Such trees are worth saving. They should be marked and protected by retaining a buffer of adjacent trees, especially on the south and west sides of the possibly resistant trees.

     For further information on BBD, the Insect and Disease Laboratory of the Maine Forest Service has available a recently revised information sheet.