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.