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Life's a beech - & then you die.

A tiny insect and a parasitic fungus are on a rampage among these silvery-barked northeastern hardwoods.

Walk through a mature forest in New York, and you are bound to notice an abundance of seedlings and saplings bearing long, cigar-shaped buds--the unmistakable mark of the American beech. Yet if you glance skyward, you won't find the beech's shiny bole and dense crown among the majestic red oaks and sugar maples of the canopy. In many areas, the climax beech tree of today takes the form of a rotted snag or a mangled sapling with raised lesions and defective bark.

Welcome to the "aftermath zone" of the beech-bark disease, an epidemic spread by a tiny yellow scale insect and a parasitic fungus. In this portion of the northern hardwood forest, the scale and fungus are now permanent residents. Not too many years ago, they killed and feasted on the great, old stands of beech and today take refuge in the smaller beech that are trying to regenerate.

Forest managers cannot stop the spread of the disease as its "killing front" moves south and west from New York. However, research has shown that a small percentage of survivors are actually disease-resistant. This encouraging news may allow foresters to grow high-quality beech in the young stands that are emerging following the epidemic's initial wave.

The tiny yellow insect, known as the beech scale (Cryptococcus fagisuga), caught a ride from Europe to the New World around 1890, landing first in Nova Scotia. The scale uses its piercing-sucking mouthpart, known as a stylet, to penetrate the thin bark of the beech, and then it feeds on the living cells within. From late summer to fall, the nymphs (called "crawlers") emerge to feed, often traveling on winds miles from their birth tree.

Most of the actual damage to the tree is due to fungi in the genus Nectria that are able to kill the beech's cambium (the layer just beneath the bark), which is stressed by the scale infestations. Depending on the tree's age and health (and to a lesser extent other environmental conditions), the fungus can cause just a few localized lesions or can lead to the decay of the entire cambium layer and subsequent death.

In 1920 the first signs of the disease did not alarm lumbermen, especially since beech had little commercial importance then. But later, as massive infestations wreaked havoc on the beech of eastern Canada and Maine, an effort was made to salvage for firewood harvest-sized trees that showed early signs of the disease. By the 1940s the disease had spread well into eastern New York, and today it extends as far west as Ohio and as far south as West Virginia.

The movement of the disease through a given locality has been arbitrarily divided into three stages: the advancing front, the killing front, and the aftermath zone. In the advancing front, the forest consists of many old, large beech trees with scale populations that are quickly multiplying. In the killing front, beech scale is rampant, Nectria attacks are frequent, and beech mortality is high. The aftermath zone, which characterizes most of New England, has suffered large mortality in the past and is comprised of endemic populations of the disease agents with a few large residual trees and many stands of young beech.

It is in the aftermath zone that foresters and private woodlot owners face their greatest challenge. The roots of each dead beech tree are able to support the growth of several new sprouts. Sprouting, also called "advanced regeneration," allows beech to spread quickly. But it is causing numerous problems for foresters, especially in Maine, where beech mortality and harvest--widespread in the 1930s and 1940s--have resulted in the growth of large thickets.

These young stems are genetically identical to their parents, so the number of beech trees susceptible to the disease has increased in recent years. Most scientists believe that a greater diversity of tree species will limit the damaging effects of the disease (when beech is interspersed with other species, the scale has greater difficulty finding host trees). However, in these emerging, dense stands, other species are crowded out. These factors have set the stage for the possibility of an even worse beech-bark epidemic once the new stems reach the minimum size to support the scale (about four inches thick).

According to Dr. George Hudler of Cornell University's plant pathology department, improved techniques for drying lumber have made beech a much more valuable species. Therefore it is essential that a management strategy be found that allows beech to regain its former glory.

As it turns out, research by David Houston of the U.S. Forest Service's Northeastern Forest Experiment Station has revealed that undamaged trees in the aftermath zone were actually resistant to invasions of the scale, even under conditions favorable for the insect. Root sprouts from these individuals will also be resistant. Unfortunately, these resistant individuals are widely scattered, so a quick fix is not feasible.

However, one management scheme offers hope to the downtrodden beech. If successful, this plan will not only reduce the proportion of susceptible beech in forests where second-growth thickets are dense but may also foster the spread of trees that are not bothered by the scale.

The first step focuses on educating forest managers about the variations in symptoms of the disease. This is important since the obvious external signs relate to a tree's disease resistance.

Beyond that, heavily damaged trees, with the characteristic sunken lesions and dead bark patches, should be culled (possibly for lumber, if the damage is not extensive). Trees with smooth bark are probably resistant and should be selected, or spared, so that they can regenerate a more vigorous stand.

Trees with raised lesions or blocky bark are susceptible to the disease but normally display enough vigor to continue to grow and prevent the scale from establishing itself. These "borderline" trees, in addition to their often overlooked economic value, often can continue to supply mast for wildlife. Houston believes this consideration is important, because in cases where only the most resistant trees are left, he has noticed extensive bark damage by foraging bears that have only a small number of beech trees to depend on for food. This easily overlooked effect of the disease is a prime example of the intricacies that must be considered in developing an effective forest-management plan.

Recent research by Jones and Raynal of the College of Environmental Science and Forestry at Syracuse suggested that beech harvested in winter shows a marked decrease in root sprouting compared to beech in summer-harvested stands. If this is confirmed through work Houston is doing in Maine, managers will need to consider relative tree resistance when planning harvest schedules.

More importantly, managers may find it worthwhile to check stands periodically, so trees that develop symptoms can be harvested before the fungus penetrates through the inner bark, causing defects. The stumps of culled trees can be prevented from sprouting if they are girdled and then treated with glyphosate (sold as Roundup by Monsanto).

In many areas of the Northeast, some sort of deer control is necessary to allow maple and birch seedlings--favorites of the whitetail--a better chance to survive within the regenerating beech thickets. Continuing research into the site conditions, forest compositions, and bark anatomies that reduce the susceptibility of beech will further improve current management practices.

Beech-bark disease will continue to spread as long as susceptible beech are around to host its causal agents. But in intensively managed aftermath zones, the American beech might one day regain its proper place among the sugar maples and yellow birches of the forest canopy.

A recent graduate of Cornell University, Jay Cammermeyer has done research in plant pathology and forestry at Hubbard Brook Experimental Forest in New Hampshire.
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Article Details
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Title Annotation:Forest Health; insect and fungus infestation of US forests
Author:Cammermeyer, Jay
Publication:American Forests
Article Type:Cover Story
Date:Jul 1, 1993
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