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(Please note: the Campus Nature Trail at Penn State New Kensington is no longer accessible for hiking. The notes and observations about the trail that are included in this essay were made in the early 2000’s.)
Spicebush Trail. Photo by D. Sillman
(References will be listed next week after Part 2!)
The section of the Campus Nature Trail called the Spicebush Trail gets its name, logically, from the dense, surrounding growth of spicebush (Lindera benzoin). The tall arching branches of these shrubs form a tunnel over a good part of the trail, and the scent of their aromatic leaves is quite pleasant in the damp, cool mornings of late spring and early summer. This tunneled trail goes down a gentle slope and ends at a footbridge that crosses a small, seasonal creek. If you cross the bridge, you can walk to stand of witch hazel (Hamamelis virginiana) and overlook a low, oxbowed section of streambank that is full of skunk cabbage (Symplocarpus foetidus). If you turn left at the bridge, you can walk up the steep Ravine Trail to the drier, upland trail system that crisscrosses through an oak and poplar forest.
A few steps up the Ravine Trail is a large American beech tree (Fagus grandifolia). Its trunk diameter at breast height is almost two feet, and it stands over 60 feet tall. Its very distinctive, light gray bark is lumpy and marked by old wounds and frost scars that have repaired themselves in thick dark circles and lines. Fortunately, no one has carved their initials or statements of love and devotion into the bark of this tree. Beech trees are frequently decorated with messages and graffiti, and these scars carved into the bark will persist for the life of the tree (Rushmore, 1961).
The bark of the beech is also one of its significant weaknesses. Its thin, fragile nature makes the tree vulnerable to insect damage, disease and fire (Tubbs and Houston, 1990). There are more than 70 species of decay fungi that attack American beeches, far more than affect any other hardwood species (Hepting, 1971). The common observation of large, old beech trees having hollow trunks and rotting limbs is reflective of its great sensitivity to fungi.
Photo by K. McFarland. Flickr
Unlike most other hardwood trees, the American beech retains its smooth bark throughout its “mature” years. The American beech can live for three hundred to four hundred years and can frequently reach heights of eighty feet and diameters in excess of three feet. In the shaded conditions of a forest stand, the American beech forms a long, straight, massive trunk that rises into a small, dense crown of foliage. In sunnier, more open sites, the American beech forms a short (although still massive!) trunk that diverges into a large number of horizontal branches that make a huge, widely spreading crown.
The American beech is found in sites that have moist soils. Beeches are especially abundant along streams and creeks, in bottom lands, and in shaded, protected ravines. Any site, though, with adequate soil moisture will support the American beech. Its root system is shallow and widely spreading which adapts it well to wet conditions. It is able to sprout new seedlings from its roots and often dense thickets of these root-sprouted seedlings are found around older, undisturbed trees (Tubbs and Houston, 1990). The tendency of beech to root sprout affects the genetic distribution of the beech trees in a forest. It causes them to grow in clonal clumps especially on sites that have been stressed or disturbed (Houston and Houston, 1994)(Morris et al., 2004).
The leaves of the American beech are also quite distinctive. They are from two and a half to six inches long and two and a half inches wide, elliptical in shape with many parallel side veins and coarse, saw-toothed edges. They are dull green above and lighter green below and turn yellow or brown in the autumn (Harlow, William M., et al. ,1979).. The leaves may remain attached to their trees through the winter (discussion below). These leaves decompose relatively slowly and are, therefore, found in thick layers on the soil surface beneath the trees (Forrester, McGee and Mitchell, 2003).
There are a number of American beech trees along the ravine and many more particularly on the north facing side of the slope down to the creek. A few of the trees are as large as the beech on the Ravine Trail, but most are smaller. Throughout the surrounding, brushy forest there are many beech seedlings and saplings and pole trees, too. Beeches seem to be thriving in this section of the forest.
There is an American beech in Michigan (mentioned in Tubbs and Houston, 1990) that stood 161 feet tall and was 53 inches in diameter, and another (mentioned in Carpenter, 1974) that was 91 feet tall with a diameter of 70 inches. Often these very large beeches are hollow due to heartwood rot.
The American beech was, according to the earliest land survey, “witness” tree records, the most abundant tree across the northern tier of Pennsylvania (Lutz, 1930)(Whitney, 1990, 1994). In Hearts Content National Scenic area in Warren County, Pennsylvania there is a patch of virgin forest that includes a number of American beech trees that are 300 to 400 years old. They are being ravaged, though, by Beech Bark Disease and a host of insect pests and may be approaching the end of their lives (Old Growth Forest Network, 2020).
The American beech is a tree of eastern North America. It is found from Canada to Florida and west to Wisconsin in the north and Texas and Oklahoma in the south. Prior to the last glaciation, though, its range was thought to extend all the way across the continent to California (Rushmore, 1961)
There are two critical physiological characteristics of the American beech that enable them to persevere and thrive in their habitats. These same two characteristics, though, also help to explain why the vast beech forests of northern Pennsylvania did not recover from the trauma of the clear-cutting that occurred a little over a century ago when the American beech went from the numerically dominant tree in these forests to a relatively uncommon species confined to stream sides and wet ravines.
Photo by J. Barker, NPS
First characteristic: the American beech needs a great deal of water to survive. It uses twice the water for growth and transpiration than that used by either oaks or pines (Tubbs and Houston, 1990). The consequence of this characteristic is that beeches must grow in places that are very moist. This high moisture requirement also affects the distribution of the American beech both geographically and topographically. Locales with very high summer temperatures are avoided (the American beech is a tree of high altitude in the southern extremes of its range), and sun drenched, south facing slopes are less preferred than the shadier, and thus wetter, north facing exposures (Fowells, 1965).
Second characteristic: the American beech has a very slow rate of metabolism. This feature enables the tree’s seedlings and saplings to persist in low energy, suppressed states for many years under dense, shading over-stories as they wait for possible breaks in the canopy above them to release them into a growth phase. American beech is the most shade tolerant tree throughout most of its range ( Loach, 1970), but its slow metabolic rate effectively prevents it from competing with faster growing hardwood species when sunlight becomes available. If there are white ash trees or birches or red maples in the under-story mix, these species will spring up into the open canopy at growth rates much greater than the American beech (Logan, 1973). For beech to succeed, then, it must be the predominate seedling in the under-story at the moment of release.
The American beech, then, will reproduce and succeed on a site that is cool, moist, and well shaded. Its success will be even more pronounced if the levels and duration of these cool temperatures, high moisture levels, and lack of sunlight are so stressful to other, less tolerant, hardwood species that many or most of their seedlings fail and die. The American beech’s ability to endure and grow very slowly for decade upon decade in these stressful conditions is the essence of its competitive edge. Alterations of a site that generate widespread soil and litter exposure to direct sunlight (and clear cutting would be an extreme example of such an alteration) will warm and dry the soil/litter system, and stimulate growth in the faster growing, less shade tolerant tree species. Such an alteration, then, erases the American beech’s competitive edge and makes the success of other tree species (like birch, black cherry, red maple, white ash, etc.) more probable.
Beech mast. Photo by D. Mullen, Flickr
Beech mast is an important food source for many birds and mammals (including black bear, white-tailed deer, chipmunks, foxes, red squirrels, gray squirrels , porcupines, martens, mice, ruffed grouse, red-headed woodpeckers, white-breasted nuthatches and blue jays) (Tubbs and Houston, 1990)(Faison and Houston, 2004) (Adirondacks Forever Wild, 2020). Beech mast was also the favorite food of the now extinct passenger pigeon ( Ectopistes migratorius ). James Audubon described the formation and movement of the great flocks of these birds as primarily a behavior designed to seek out and consume beech nuts (Rushmore, 1961). Many of these birds and mammals contribute to the widespread dispersion of beech seeds through their feeding on and possibly burying and caching of the beech mast.
Other parts of a beech tree also supports a wide variety of bird species. White-throated sparrows eat buds and blossoms in the spring, hairy woodpeckers and scarlet tanagers preferentially forage for insects among its branches, wood ducks utilize tree holes in beeches for their nests, and Cooper’s hawks, northern goshawks, American redstarts and a long list of other birds make their nests in beech branches. (Adirondack Forever Wild, 2020).
Beech trees are also very important in the quality and nutrient composition of the forest soils. Beech leaves are rich in nitrogen (they contain 3% nitrogen, the highest value of any tree in the forests of eastern North America) (Latty, Charles and Marks, 2004). Its leaves also tend to accumulate under the tree of origin and form thick, slowly decomposing mats of organic materials which effectively mulch out possible nutrient and light competing herbaceous growth and other tree species (Forrester, McGee and Mitchell, 2003). This can be very important to the reproductive success of the beech because sites with thick, forest floor underbrush can shelter large numbers of beech mast consumers that are capable especially in low mast production years of eating a very high percentage of a tree’s mast production (Royo and Carson, 2008).
Ferns can have a negative effect on the rate of seed germination and growth of seedlings of many species of trees (including birches, black cherry, pines, and oaks) (Horsley, 1977 a and b) (George and Bazzaz, 1990 a and b). Neither ferns nor raspberry cover, though, have, however, a negative effect on the germination and survival of American beech (Tubbs and Houston, 1990).
Photo by K. Schultz, Wikimedia Commons
The American beech’s ability to sprout from the stumps of young trees gives it a competitive edge over non-sprouting species in any successional race triggered by disturbance. The growth rates of the sprouts, though, are much slower than the seedling growth rates of the less shade tolerant hardwood species with which they typically compete. A significant, successional advantage that American beech sprouts and seedlings do have over all of their potential hardwood competitors, though, is the beech’s “virtual immunity to deer browsing.” White-tailed deer, which are one of the primary sculpting forces of our present day forests in Pennsylvania, seldom eat beech seedlings or sprouts (Tubbs and Houston, 1990).
The ability of the beech to vigorously root sprout, its high levels of shade tolerance and very low metabolic rate, its ability to mulch out forest floor competitors, its ability to tolerate the potential allelopathic effects of ferns and other forest floor plants and its “immunity” from deer browsing allow the species to persist in and even come to dominate many mixed hardwood forests. In beech and sugar maple forests in Ontario, for example, it is expected that beech trees will predominate over the maples over successional time (Brisson, et al., 1994).
(Next week: the American beech, Part 2!)