Sunday, April 26, 2009

4-26-09 Beech Bark Disease, the archaic forests of New England, and the future

The snow has melted back uphill to a little over 2500 feet on the north-facing slopes so the woods below that, and the trails, are pretty much free of ice and snow. There's still a huge amount of snow above 3000 feet. I took a quick afternoon hike last Saturday intending to go up Mt. Adams but got as far as Madison Hut at 4800 feet and turned around as the weather above was perfectly wretched with no visibility and cold. Of course, by the time I got well down the Valley Way Trail, the clouds dispersed and the sun was fully out and it actually got hot.

The reason for heading up the Valley Way in the first place was to visit a large grove of mixed hardwoods, mostly beech and sugar maple, that I've been studying for a number of years. The grove begins at the 1500 foot contour line between the Airline Trail and the Valley Way and extends uphill to about the 2500 foot contour line. Over several decades the grove has been host to Beech Bark disease (BBD) that has caused a high mortality of American beech (Fagus grandifolia Ehrl.) throughout its present range from eastern Canada, New England and BBD has now ventured as far south as West Virginia. Beech Bark Disease is also referred to as Beech Scale and is caused by infestations of a tiny insect called Beech Scale, Cryptococcus fagisuga, coupled with a tree killing fungus Nectria coccinea var. faginata (sometimes it's a relative of coccinea by the name of Nectria galligena). The scale penetrates the bark of the beech trees and then the fungus, the Nectria, moves into the opening made by the scale and eventually kills the tree. The kill-time varies, I've found, and in this grove trees have surivived with the Nectria for a decade.

The photo above is of a tree that has been fairly healthy during the 20 years I have been studying this grove. However, the tree is beginning to show signs of BBD with the white, waxy deposits you can see on the lower part of the trunk towards the camera. Just to get you oriented I'll repeat that this tree is growing on the north slope of Mt. Madison in the Presidential Range of the White Mountains in the White Mountain National Forest in north central New Hampshire (in the US). The tree is growing on the 1500 foot contour line (1500 feet above sea level) between the Valley Way Trail and the Air Line Trail.

In this photo of the beech-sugar maple grove on Mt. Madison the beech trees in the right foreground are infested/infected with BBD but the other individual beeches appear to be disease free. I've found that in this grove there are a number of trees that do not become infested 1.) at all but are relatively few, or 2.) only after a significant period of time and not relative to other trees close by which are infected even with DBHs as low as 3 inches.

Along with sugar maple (Acer saccarum) beech is a dominant tree in the eastern Boreal Forest of North America. It is deciduous, grows to maturity in roughly 100 years, and lives for up to 250 years in groves like the one I'm observing on Mt. Madison. Some American beech have been ring-counted to almost 450 years old but that is not an average age at maturity. Beech have been a component in the northern forests for many thousands of years, possibly 7,000 years but definitely for 6,000 years.

In "The Story of Vermont" by Christopher McGrory Kylza and Stephen C. Trombulak published by University Press of New England about 10 years ago the authors cite the appearance of a number of deciduous trees including beech, American chestnut, sugar maple, yellow birch and hemlock in the pollen records beginning 8,000 years before present (BP). they also cite the appearance of spruce, dwarf white birch and a variety of low lying plants like ground pine and ferns in the pollen record dating to 10,000 BP. They concluded that the last glacial sheet, the Wisconsinan, retreated from Vermont by 12,500 BP which is a little earlier than other reports I have read. Earlier in this blog I set 11,000 years BP as the time of full ablation. As to the beech, Charles Cogwell and others, in a number of different texts, have set dates a little later (e.g. 7000 years BP) for it's having achieved the northern limits of its migration from the south into the post glacial areas of the north.

There are a number of healthy saplings in the photo above that are part of a characteristic pattern even where BBD is heavily infested. Like a number of other species Beech reproduces by both seeds and by sprouting. The saplings in these photos may have sprouted from the roots of older trees or they may have come from seeds. At any rate, for the moment they are disease free but will they stay that way? Researchers have shown that some trees are resistant to the scale and remain disease free even in groves were there is a heavy loss from the BBD.

I became aware of BBD in the mid-1960s working as a research assistant at Hubbard Brook Experimental Forest in West Thornton, NH. Later, in graduate school, I did a small research project on BBD in a grove of mix hardwoods on West Mountain near Keene, NH. That project attempted to measure variables that included the density of beech in the grove on West Mountain, average size (mean diameter-at-breast-height or DBH), degree of slope (steepness), aspect (the direction of the slope), pH (acid content) of the soil, wetness, average wind direction, average temperatures, and crown density.

BBD began it's cataclysmic journey in Halifax, Nova Scotia, in the late 1800s. It arrived in North America aboard a ship loaded with European beech seedlings planned for a city park in Halifax. The scale travels primarily as a wind-born "coccus" and moving west and south was difficult given the prevailing north westerly winds in Nova Scotia. The beech scale, however, reached New England in the late-1950s and was first sited in Maine.

In my West Mountain research site I was trying to see if there was any correlation between BBD and "Acid Rain" which became a phenomenon in the mid-1960s. My interest was whether increased soil pH (higher amounts of acid deposition) might decrease the resistance of the beech to the BBD. A larger question on my my mind was whether acid rain was exacerbating a decline of biological integrity in the northern forest. My results were inconclusive. I did see patterns, however, that BBD skipped some trees that appeared resistant to it. It also seemed to appear only on trees with a DBH of 8 inches, or greater, and it appeared to attack the trees first on the damper, shaded northern side of the trees.

This is a trunk of a beech tree which is infested/infected and by my observations was not infected 5 years ago. Contrary to earlier research I did in Keene, NH, the disease has spread to all sides of this tree and infested/infected the tree before it was 8 inches DBH.

The American beech tree is a gorgeous tree of immeasurable importance in the northern forest as a "mast" tree, or one that provides essential food for the forest's other inhabitants including small and large mammals. Mast is the seeds, nuts, and other edible parts of trees that are the primary diet of woodland animals. A short list of animals that compete for the beech "nuts", or mast, every year are black bear, deer, red squirrels, and numerous birds. In the fragile but essential economy of cation exchanges, particularly with some residual impacts from acid rain, the beech also plays a role in providing valuable nutrients to the forest soil in its yearly deposition of leaves (organic matter or OM) which, in forest litter studies that I've conducted, are somewhat higher in calicium (Ca) content than sugar maples.

The three beech trees in this photo are severely infested/infected and will die from the BBD in a matter of years. The mortality rate for BBD is very high, as much as 86 percent in some areas, so it raises questions about the future of beech in the northern forest and reflects back to the historic and archaic past of the forest as well. If beech has been part of the mosaic of the northern forest for thousands of years then it must have gone through some ups and downs in that time period. Remember that everything's in flux and forest goes through substantial changes in a 1000 year period. Insects, ice storms, warming periods, cooling periods, all represent stressors that impact growth, stability and longevity. Cooling periods would favor some trees like spruce and fir but might force beech or sugar maple into a decline, or a migration to a warmer part of their range. Then, a 1000 years later it might warm up again. One degree centigrade rise or fall could cause these kinds of changes. When we think about homeostatsis, the "center" around which the flux occurs, we are not talking about a constant like a ship with a gyroscope and an even keel, we are talking about constant adjustment and readjustment, constant impact, adaptation, and shifts. It's more like a ship under sail that has to beat up wind by tacking back and forth.

This tree is badly infested/infected and has a DBH of about 8 inches. It was on my disease count list three or four years ago and the disease has progressed considerably. The tree in the photo below looked like the top one four years ago. It will probably succumb within three or four years. BBD is efficient. Like human pathogens it has a job to do and if unchecked will just hammer away and continue to kill off huge amounts of biomass. Is it Darwinian? Does it serve a purpose?
In a little over 100 years it has caused a large-scale change in the Northeastern forests and continues to do so. Has it's advance been exacerbated by other phenomena like global warming, acid rain, or a general decline in forest soils since the last glaciation?

BBD is specific to beech, both European and American beech. The disease emanated from Europe and was introduced fairly suddenly. It's young, comparatively, and virulent. Chestnut blight was introduced to the New World in much the same way as BBD and within a short period of time it killed all the chestnuts in the country above a certain DBH. Dutch Elm Disease was another. Elms are still around. They are still in the forest but they don't make it to maturity. They get the disease at a certain crown height and die in a few years. I took part in an experiment using an antibiotic for Dutch Elm Disease developed by Dupont in the last 1960s which was gravity fed into the root system of mature trees with the first signs of infection but the interventions failed. The Hemlock, (Tsudotsuga canadensis), an eastern tree that has been around for thousands and thousands of years has also been compromised by a tiny organism introduced from Asia. Thousands of them have died. The chestnuts died so quickly from the spread of the novel blight that they did not have a chance to evolve counter strategies. It's possible that by human interventions involving hybridizing elms and chestnuts a new, resistant variety of the two species can be introduced.

The leaf mat under the maples and beeches is valuable. It contains food for animals. In the lower photo you can see a discarded beech nut casing left there by an animal recently. The mat, or carpet I sometimes call it, also contains the makings for soil in the form of organic matter and lots of cations and anions that help in the chemical reactions of photosynthesis and respiration. For the moment, in the first hot days of spring before the leaf canopy appears the leaf mat will keep the soil moist by keeping the sun and wind from drying it out. This site on the north side of Mt. Madison is "mesic", meaning in the middle between wet and dry, but in the late winter and early spring the woods here are damp and cool. When the leaf canopy is fully out in late May and June the trails here are shaded and cool. The snow that was here for five months helped press the leaf carpet down so it is flat and it also flattened the evergreen wood fern you see in the photo. The fern will be straight and tall in no time.

This is a beech that has succumbed to BBD. It is now host to Climacodon septentrionalis, a common shelf fungi, that will help break down the wood into more usuable and soluble form. It's sad to see the trees at this and the next stage of their demise. What will become of the beech and the forest itself? Will the beech disappear in time? How will that impact the other species, the sugar maples, yellow and paper birches, the white and black ash, the poplars? The great Laurentide forest stretching from the Arctic tundra to the Mississippi and south was and still is one of the most biologically diverse ecosystems on Earth. Beech has been a major component in that ecoystem for thousands and thousands of year and the fact that in a little over 100 years the beech have been dealt a mortal blow is Earth shattering. It's a major tremor. How will the forest adapt? Think of that huge forest, vast beyond belief, covering more than half the continent, with thousands of species of plants and animals in motion, all in a state of becoming; species advancing, dominating, receding, dying out completely, others receding for a time and then advancing again as favorable conditions evolve. The White Mountain National Forest is a tiny remnant of that huge biome, a splinter, a hologram, a reminder, that life is astonishing as is death, the death of a tree or a whole specie of trees, and that we watch and observe and measure and theorize but we are part of that fabric.

These two trunks in the photo above and below are from beech trees that died several years ago from BBD and are now returning to molecular states. I don't know what happens to the scale and the Nectria when the tree dies, if they move in tandem to the next available tree, or not. It makes sense that the disease, the scale and the fungus, are both fed by their labors and it makes sense that they would be reproducing while destroying the beech so it also makes sense that the disease would continue indefinitely which is what it is doing. The Chestnut Blight just kept going until there was nothing left.

Think of that huge forest, vast beyond belief, covering more than half the continent, with thousands of species of plants and animals in motion, all in a state of becoming; species advancing, dominating, receding, dying out completely, and others receding for a time and then advancing again as favorable conditions evolve. The White Mountain National Forest is a tiny remnant of that huge biome, a splinter, a hologram, a reminder, that life is astonishing as is death, the death of a tree or a whole specie of trees, and that we watch and observe and measure and theorize but we are part of that fabric. We were here when it was huge and thriving, 10,000 years ago, and we are still here as witnesses.