Wednesday, February 29, 2012

Forests: The Blight of Beech Bark Disease

For more than fifty years, woods walkers in the Adirondacks and elsewhere have learned not to take the beautifully smooth, “thin-skinned” bark of the American beech tree (Fagus grandifolia) for granted. Our grandparents grew up suddenly missing the American chestnut as the blight of 1900 quickly decimated that species as a dominant tree in our eastern woodlands, along with its innumerable cottage and industrial uses, and its sustenance for so much of our native wildlife.
Those born in the 1950s as I was have been missing the great American beech trees whose dominant individuals graced forests from the Canadian Maritimes and New England through the south and midwest. Beech bark disease (BBD) has killed them. The causal agent is the beech scale insect (Cryptococcus fagisuga Lind.). The tree is then invaded and killed by several native Nectria fungi. The scale insect was introduced from Europe, and reached New Brunswick and Maine around 1930. The disease reached the Catskills via the port of New York City by the 1950s, and the Adirondacks a decade or so later.

The introduced scale insect, invisible to the naked eye, covers themselves in a very visible white wooly substance on the bark which elicits beech tree lovers to groan “this one’s got it too.” This cover allows the insect – all females – to feed on the tree undetected, and lay eggs. The insect employs asexual reproduction; its eggs do not require fertilization. Then, the killing agents, Nectria fungi, invade where the insect has somehow altered the bark, perhaps through miniscule punctures made to feed on the bark. Then, future observers may see the orange fruiting bodies of the fungi. The killing phase, almost overnight, it seems, leaves that beautiful big beech bark skin pockmarked and cankerous. Other fungal and insect invaders follow. The beech is girdled. It dies in place over time, or snaps off, but its roots are very much alive and send up beech “whips” to soak up the sunlight in the giant’s living space; they in turn are invaded by the scale, do not fruit like the giants that preceded them, yet thoroughly shade out the understory.

Ecology professor Donald Leopold (SUNY College of Environmental Science and Forestry) takes note of the half to one acre gaps that have been created in the heart of old-growth regions of the Adirondacks owing to BBD. BBD “has only been here in this century, and we cannot do anything about it.” Not only does BBD limit the amount of beech nuts available for mammals and birds, but “the sprouts on the understory will grow for many years and eventually die, leaving only extensive beech thickets in many of our old-growth forests” (from Looking for Answers, An Exploration of Biodiversity in the Adirondack Park, 1994 by the Association for the Protection of the Adirondacks).

I discovered this phenomenon attempting to walk across the old-growth portions of the Five Ponds Wilderness Area two decades ago. Thrashing for a full day through the witch hopple growing as thick as our arms under the opened canopy of a former old growth beech forest, we had to hand our backpacks over the giant downed beech stems and branches to our companions on the other side. As Leopold and others have observed, the advance of beech bark disease is particularly tough on old-growth beech stands which formerly contributed tremendous mast for wildlife. These naturally occur to their largest extent in the Adirondack and Catskill Forest Preserve.

In a ski into the Siamese Ponds Wilderness this month I noted how smaller second generation beech which grew from the root suckers of their dead elders in the 1980s are now thick with scale insect “wool,” and cankered thanks to the nectria and other fungi. This disease seems to exhibit an endless capacity to reinfect the beech whips which emerge from the living roots. Beech scale insect populations must have built up to high levels over 60 years, and while one or more species of ladybugs and some fungi may prey on them they do not yet appear to exert a controlling influence.

The vulnerability of the American beech to the scale insect also leads to the question of why this tree evolved with such a thin bark. The photosynthetic advantages of one of the extremely thin inner bark layers apparently provides significant growth and cell maintenance advantages during leaf-off seasons; the smooth bark discourages growth of moss and lichen which would tend to block photosynthesis.

I get exhilarated when I go outside and find uninfected or resistant beech, as I did just a mile from my home in Saratoga County. No large, protected wilderness here. On a 100–acre woodland tract growing between north of Clifton Park’s subdivisions, Round Lake and I-87, where a developer wants to build hundreds of homes, is a stand of smooth-barked, seemingly healthy American beech. Just north, at the protected Saratoga Spa State Park, is another beautiful stand. What do these uninfected beech stands signify? Genetic resistance? Unfavorable (to scale insect) chemical composition in the bark, or site conditions that favor resistance? Something else? I believe these sites should be catalogued and preserved to ensure that a wide variety of healthy beech specimens are available for ongoing efforts to breed and spread resistance. Please, more informed readers, let us know more.

Photos: Uninfected beech stand in Saratoga County and a beech tree infested with scale insect, Siamese Ponds Wilderness.

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Dave Gibson, who writes about issues of wilderness, wild lands, public policy, and more, has been involved in Adirondack conservation for over 30 years as executive director of the Association for the Protection of the Adirondacks, executive director of Protect the Adirondacks and currently as managing partner with Adirondack Wild: Friends of the Forest PreserveDuring Dave's tenure at the Association, the organization completed the Center for the Forest Preserve including the Adirondack Research Library at Paul Schaefer’s home. The library has the finest Adirondack collection outside the Blue Line, specializing in Adirondack conservation and recreation history. Currently, Dave is managing partner in the nonprofit organization launched in 2010, Adirondack Wild: Friends of the Forest Preserve.

6 Responses

  1. Ellen Rathbone says:

    Here in Michigan I am tickled pink to find uninfected beech trees…and folks around here think I’m nuts. Apparently BBD hasn’t really hit home here…yet. On the other hand, the emerald ash borer has wiped out the ash trees. I see a trade happening here: we will be getting BBD, while the ‘dacks will be getting EAB.

  2. Paul says:

    I wonder if this (so far) mild winter will speed that bug in this direction?

  3. Paul says:

    According to the Forest Service the scale was accidentally introduced into Nova Scotia in 1890. It spread pretty slowly and has finally hit NY.

    Why is or was there never a ban on moving wood like we have for EAB for this? My guess is there are many more Beech trees in the Adirondacks than ash. Why the difference in policy?

    I always see things like scotch pine trees pop up in log landings after a logging operation has left an area. These are clearly “invasives” being introduced to an area from the logging equipment (perhaps fertilized seeds stuck in the treads of a log skidder). What is it that commercial loggers are required to do to keep them from spreading stuff unintentionally. They more than anyone have a stake in things not spreading around. The ones that I talk to are actually some of the best stewards around. I wonder if there isn’t more that they could be doing. Maybe even just making sure they wash their equipment before the leave one operation and move to another.

  4. Lee says:

    Have to say I have not seen this BBD affect whole stands of trees. Will definitely keep my eye peeled for it, feel sure i have seen this on the odd mature Beech.

    I’m in London, UK by the way


  5. Lawn Service Orlando says:

    From Akron Ohio I remember those beautiful trees when growing up. And seemed like suddenly I didn’t see as many Beech trees as I once did. Now I know the reason why. Now living in Orlando Florida – Not many if any Beech trees in this area, sure do miss them.

  6. David it has been my observation that the American Beech bark disease seems to have the had the most impact in the areas of New York that have seen the most of many decades of acid precipitation. I grew up near the waters of Piseco Lake in southern Hamilton County. I saw the end of the last Giants smooth barked and many well over 100 ft with broad healthy crowns.The largest trees were all gone by the mid 1970s with only an occasional tree of size left to discover on some ramble off trail.The fungus is now attacking root sprouts of only a few inches in diameter.
    I have been in many parts of the northeast in the past decade where i have observed Beech that are massive in girth and hight.The larger ones are in areas that have odd reasons for protection such as old residential areas and large estate developements. There are many large healthy Beech in most areas of this state even in the towns of the Mohawk valley just to south of the Adirondacks. I observed some of the largest and oldest trees just north of Philly PA. in Gladwyen PA.That area of the suburbs was mainly horse farm estates and is now comprised of smaller lots.The area is loaded with american beech that reach at least 100 feet and rivaal the size of the Oaks and the Tulip Poplars they share the forest with.
    I have allways suspected that acid precipitation could some how cause the American Beech to be stressed to the point that allows a normally harmless existance with the fungus to become a deadly one.I aalso suspect that the fungus has allways been here and that other insect damage and broken branches from storm damage would caused the same fungus to invade the trees circulatory system.I had many conversations with my Great Grandfather and many other old timers growing up in Piseco and many said the beech were very healthy till the 1950s and that also coincides with the acid precip. and all its studied affects.

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