Illustrations by Dr. Fred Paillet about American chestnut
Some of you may be aware that Dr. Paillet has been a major contributor to the training for the Appalachian Mountain Club Mega Transect project. Anyone who has read Dr. Paiilet's papers is aware that he is a master observer – one who draws meaningful inferences from details in the clutter of a forest floor. In recognition of this skill, and how it will be leveraged for this project, I've reproduced, with Fred's permission a series of his illustrations and accompanying descriptions of observations along some southern sections of the Appalachian Trail.
I am sure reading these notes has helped make me a better observer, and I hope it will do the same for you.
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| Figure 1 – [click to expand] Illustration courtesy of Dr. Fred Paillet |
Figure 1. Chestnut stump along the Appalachian Trail about two miles north of Springer Mountain, Georgia. This is the old stump of a blight-killed chestnut adjacent to an AT shelter, and is compared to a living chestnut tree in the same drawing. Based on tree-ring studies from the area, this tree was killed by blight sometime between 1935 and 1940. The flat top of the stump suggests that the tree was cut in the timber salvage operations typical of that era. Compare this stump to the base of a similar-sized living chestnut in West Salem, Wisconsin. That living and vigorous canopy-dominant tree had a dwarfed basal sprout growing from the suppressed buds on the root collar. A much larger population of living European chestnut sampled in Russia shows that these dwarfed basal sprouts are not unusual even when there is no damage or disturbance to the “parent” tree. Examination of chestnut trees killed by logging in West Salem showed these little sprouts grew from “bulbs” of tissue embedded in “sockets” in the root collar. A similar socket is clearly present in the old stump in Georgia, indicating that this tree also had one or more basal sprouts even before it was stressed by blight. Studies show that chestnut root collar sprouts develop their own root systems and are largely independent of the root system of the “parent” tree. These independent little trees have a very difficult time in surviving when they are isolated by a surrounding mass of wood, explaining why most living chestnut sprouts we see today originated as old seedlings that never attained large size. At the time this figure was made, sessile trillium and bloodroot were just bursting into bloom in the leaf litter along the trail.
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| Figure 2 – [click to expand] Illustration courtesy of Dr. Fred Paillet |
Figure 2. Chestnut sprout clone about one mile north of the AT crossing of US route 129, Neels Gap, Georgia. Most of the live chestnut sprouts observed along the AT looked like this. Sprout stems were small trees up to an inch or two in diameter and maybe 15 feet tall, occurring as single little trees or pairs of trees. They had clearly originated after a previous stem had been killed by blight, as indicated by the presence of old, deeply weathered wood from similarly sized stems. Almost all of the sprouts seen in April 2008 were recently killed by blight, or impacted by one or more active blight cankers. The incidence of blight is probably explained by the often-noted tendency for blight to occur in “epidemics”. The basal sprouts produced by stems after they are girdled by blight remain small for many years. The numerous sprouts sort themselves into a small number as a result of blight, competition, and browsing. These remaining spouts are so small they provide very little substrate for the continued growth of the blight mycelia. The combination of a small “target” for the blight and the low level of blight in the area allows the regenerating sprouts to escape disease for a considerable time. The size of the stems in my figure indicate that this could be more than a decade. Eventually, the amount of chestnut bark available for blight infection reaches a point where a new epidemic can sustain itself, and the cycle continues. One wonders how many sprouts fail to make the transition under the stress imposed by blight and competition. A considerable number must be able to handle such adverse conditions because there are so many living sprouts today.
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| Figure 3 – [click to expand] Illustration courtesy of Dr. Fred Paillet |
Figure 3. Standing chestnut snag adjacent to the AT about two miles north of Neels Gap, Georgia. Although large chestnut trees in this area must have been killed by blight before 1935, some standing chestnut snags can still be seen along the AT today. In general, there is a wide variation in the state of preservation of chestnut logs and stumps along the southern part of the AT. The remains of the old chestnut forests vary from nearly intact snags such as in my figure, to badly deteriorated slabs of chestnut wood scattered in the leaf litter. The best preservation occurs when snags remain standing, or when fallen trees are propped up off of the ground by their lower branches. When chestnut logs are in contact with moist soil, they tend to rot out from the interior. The large vessels in the outermost sapwood keep the wood well-drained and free from decay. The inner heartwood has had the conducting cells plugged with resin, and this inner core of wood retains moisture and becomes more liable to decay. In time the log becomes hollow, and then the outer cylinder collapses to form a pile of slabs. This disintegration is aided by the lack of cross-connecting ray cells, which gives chestnut logs their well-known propensity to spilt into rails. But what kept the particular chestnut tree shown in my figure upright for more than 70 years? The location had something to do with it. This is a well-drained saddle in a ridge where the forest today is white oak, mockernut hickory, and basswood. Note that the snag is almost as big as the surrounding oaks, even though they have had another 70 years of growth. The leaning oak just behind the chestnut snag must have an interesting story to tell ? perhaps one of being blown over by a windstorm when no longer sheltered by the massive crown of the old chestnut.
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| Figure 4 – [click to expand] Illustration courtesy of Dr. Fred Paillet |
Figure 4. Dwarf chestnut tree attached to the stump of a large chestnut tree along the Sutton Bald Trail, Joyce Kilmer Wilderness, North Carolina. This is the exception that proves the rule. Most chestnut sprouts we see today originated as seedlings and were never attached to a large chestnut tree. When cut or damaged, chestnut trees produced abundant root collar sprouts. When free of competition, these spouts can produce new trees, even when they come from the stumps of former timber-sized logs. In the presence of competition and repeated blight damage, chestnut sprouts find a much more difficult situation, especially since the sprout root systems are not well connected to the tissue of the main tree, and must fend for themselves. The situation is even worse when the tree dies and is left standing. Chestnut wood is very decay resistant, so the aboveground part of the tree can last for a century. The roots are kept moist in the soil, and decay more rapidly. Thus, the tree eventually topples over under its own weight. Any little sprouts perched on the root collar are pulled out of the ground in the process. In this case, the stump is in the ground and the remains show that the original tree broke off above the root collar. In fact, the stump shows several stems as if the original tree was a coppice itself. I think of a storm-battered old chestnut clump on this exposed ridge. Sloughing branches and bark had been collecting for some time around the base of this clump of trees, forming a suitable substrate for the roots of the sprouts. The dwarfed chestnut sprouts that manage to live today show the continued rigors of life on an exposed ridge, but probably survive just because of those unusual conditions. Note how the shape of these stressed sprouts differs from that of most others, and that the small stems have the characteristic bark of mature trees.
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| Figure 5 – [click to expand] Illustration courtesy of Dr. Fred Paillet |
Figure 5. Vigorous chestnut sprout with fully healed hypovirulent cankers near the Wolf Laurel Trailhead, Joyce Kilmer Wilderness, North Carolina. Most of the chestnut sprouts seen today along the AT do not have the opportunity to become very large before blight cuts them down to size. Occasionally the fates decree that a combination of circumstances allow a chestnut sprout to reach substantial proportions. The tree in my illustration seemed perfectly healthy and had obviously been growing under almost full release. Death of a nearby oak had opened the canopy and this sprout clone was taking full advantage of the fact. Other chestnut sprouts in the area were being affected by blight, and this tree had a prominent blight canker on each of the three main stems. But the stems themselves showed no signs of stress. The crown was in the first stages of breaking bud, there were no basal sprouts being released, and no “water shoots” from the vicinity of the cankers. The cankers themselves seemed to have healed naturally, with a small patch of exposed dead wood surrounded by thick callous tissue. The “dead” oak associated with the release was cut in a logging operation some time ago. I think that the old piece of dead wood in the center of the sprouts was actually the stem released by the logging. This stem must have grown rapidly for perhaps a decade before being killed by blight. The canopy had still not closed, and so the basal sprouts stimulated by blight destruction of the main stem were able to grow under nearly full capacity. This process would account for the fact that the oak stump seems much older than the decade required to produce the chestnut stems we see today. Also note the recently dead chestnut stem off to the side. This is probably a sprout released with the three others, but left behind by the exuberant growth.
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| Figure 6 – [click to expand] Illustration courtesy of Dr. Fred Paillet |
Figure 6. Dense population of chestnut sprouts along a well-drained ridgetop, Slickrock Creek Wilderness, North Carolina. One of the often-noted characteristics of chestnut sprouts in our forests today is the tendency for sprouts to be clustered at particular locations. This is a typical example from the kind of clustering that was apparent at several locations along the AT in Georgia and North Carolina. This site was on the crest of a northwest-facing ridge dominated by dry oak-hickory forest with no identifiable remains of large pre-blight chestnut trees. None of the sprouts in the illustration appear attached to remains of larger trees, and all are assumed to have originated as “old seedlings”. I have deleted all other small stems (sassafras, red maple, and spindly mountain laurel) from my drawing so that the six small trees in the figure are all chestnut. Only the tiny little sprout off to the right is unblighted ?an illustration of how small targets can escape the blight. The average spacing between chestnut sprouts here is about 6 feet. What accounts for such “hot spots” of chestnut sprout occurrence? Is this an artifact of seedling establishment, seed predator dispersal, protection from browsing, or differential survival from a much denser original population? If we knew the answer, we might have a real step forward in planning the re-introduction of chestnut to our forests.
