Signs of Winter 11: Natural History of a Northern Red Oak

Photo by D. Sillman

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I have seen  many northern red oaks (Quercus rubra) along the hiking trails of Western Pennsylvania. Their very distinctive, vertically striped bark helps to them to stand out even in dense mixed growths with many other tree species. The picture to the left shows a large northern red oak along the Baker Trail just west of Cochran’s Mills.  Many of the forests in which these red oaks are found are secondary or even tertiary growth forests. The pre-settlement, primary structures of these forests were quite varied. Some were dominated by white oak, American chestnut, and yellow poplar, others by white pine, and even others by eastern hemlock and American beech. Almost all of these starting forests, though, after they were cut, ended up with increasing percentages of northern red oaks in their developing forest ecosystems.

The northern red oak is the embodiment of a generalist. It grows on a great variety of soils and is found in almost any topographic orientation (Sander 1990). It has a very broad geographic range over the eastern half of the United States that stretches north into southern Canada and into Nova Scotia (it is the most northerly distributed oak) and south to just above the Gulf coast (Little 1979). It grows best, though, in moist soils with deep “A” (upper, organic-rich) soil horizons, and on lower, concave slopes with either northerly or easterly exposures (Sander 1990).

Northern red oaks can be found occasionally in pure stands but most frequently they grow in mixed forests often with white pine, red maple, and white and black oaks. It is also associated with species like white ash, green ash, big-toothed aspen, American elm, slippery elm, the hickories, scarlet oak, and more (Braun 1950, Eyre 1980).  Its wide range of site tolerances and its tenacious survival in forests undergoing stress make it an increasingly common component of our eastern forests.

Photo by D. Sillman

Just off of the upper section of the Ravine Trail on the Penn State New Kensington Nature Trail is a large (50 foot tall, 18 inch diameter) northern red oak five yards down the hillside, growing at a fifteen degree angle up into an open section of the canopy. The crown of the oak fills a gap between the yellow poplar and black cherry trees that are quite abundant on the upper section of the slope and the American beech and red maple that grow on the bottom of the hill.

Around the base of the red oak is a dense thicket of raspberry and spice bush. There is also abundant wild grape growing on the ash trees, but none on this particular oak.

So, why is this northern red oak here?

As I have said for other trees, northern red oaks have to come from northern red oaks. So, this tree, which is about 80 years old, had to arise initially from a parental tree that was, at least somewhat, nearby. The seed of red oaks are acorns, and acorns are common foods for many large birds and many large and small mammals. Wild turkey, crows, blue jays, squirrels, chipmunks, mice, voles, and white-tailed deer all eat acorns. In a good reproduction year (lot’s of acorns!), eighty percent of a red oak’s acorns are consumed by these vertebrate consumers and also by a host of invertebrates. In a bad reproductive year, though, one hundred percent of the red oak’s acorns may be consumed (Marquis et al. 1976, Sander 1979). But, there is always a chance, especially in a “good’ reproductive year when there is an overwhelming abundance of acorns, that some of the gathered acorns may be dropped and forgotten. Most red oak acorns fall and remain near the parental tree (Sander 1990) but dispersal of acorns by crows and jays can involve surprisingly large distances.

Red oak bark. Photo by D. Sillman

For example, my house sits on two acres in southern Armstrong County. The trees growing on my property are a mix of red maple, silver maple, red pine, eastern hemlock, blue spruce, Norway spruce, slippery elm, white ash, American chestnut, apple, pear, and black locust. When we moved to this house 30 years ago there were no oaks of any kind within a three quarter of a mile radius of our house. Eighteen years ago, though, I found seven oak seedlings (three white, two black, and two northern red) growing in the partial shade under two of my spruce trees. When those spruce trees (and six more of their spruce cohort)  were blown down in a microburst a few years later, these skinny oak seedlings and a dozen or so other oaks whose presence I had not detected, started to rapidly grow! These oaks are now over 25 feet tall and are spreading their branches into the spaces left empty by the departed spruces. I assume that the acorns from which these oaks arose were deposited in my yard by some of the very abundant crows or blue jays that occasionally occupy parts of my yard and field. These trees, then, had great mutualistic assistance that enabled them to “fly” substantial distances from their parental sources.

So, our northern red oak here on the Nature Trail could have come from a parental tree a mile or more away. This parental tree, like all northern red oaks, had both male and female flowers and flowered in the spring (Sander 1990). The pollen was dispersed on the wind and a very small percentage of it was deposited in a female flower. The fertilized ova in the female flowers formed acorns (in clusters of 2 to 5) which then took two years to mature. The brown, mature acorns fell from the parental tree in September or October (Schopmeyer 1974).

Northern red oaks begin to produce acorns when they are twenty-five years old but do not produce abundant acorns until they closer to fifty years old. “Good” acorn crop years occur every two to five years, but some individual trees never make very many acorns at all (Schopmeyer 1974).

So, the parental tree of our northern red oak may have flowered in late May, eighty-two years ago and set the acorn that would become our tree. The mature acorn, then, two years later, either fell to the ground under the parental tree to wait for spring to germinate, or it was carried off by a squirrel or by a crow or blue jay, dropped, and then forgotten. The overwintering acorn was probably in contact with moist, mineral soil, and was also probably covered by a layer of fallen leaves. Contact with soil and protected, moist conditions are critical for acorn germination (Sander 1979). In the spring the acorn sent a long tap root down into the damp soil and slowly began to grow its root system (Sander 1990). It’s above ground stem and leaves grew even more slowly in cool, shade of the forest.

Overall, northern red oak seedlings grow very slowly and are extremely sensitive to drought (Seidel 1972). Their need for sunlight to drive their photosynthetic energy metabolism must be balanced against the potentially fatal, drying impact the sunlight has on the moist soil. The red oak, then, exists on an ecological razor’s edge, and this survival edge changes through the years in which the seedling grows and matures.  Shady, very moist conditions are required for germination and initial seedling survival, but as the root system develops (and there are more roots to an oak seedling than above ground stem!) the moisture stress eases and increased levels of sunlight are not only tolerated but are required to maintain existence and fuel growth. Larger seedlings will die of there is not sufficient sunlight to drive their photosynthetic metabolisms (Sander 1990).

Northern red oak seedlings, then, have very narrow, very specialized niche requirements, and the character of these requirements change through development. It is not surprising, then, that these seedlings have a very high mortality rate. Low moisture, too much sunlight, too little sunlight, animal activity (including deer browsing), fire, or insect damage can destroy the stems and leaves of these young trees. Destruction of the above ground portions of these trees, though, often leaves the below ground roots intact. New sprouts are then able to grow from these roots and are able to re-establish the northern red oak seedlings.

This cycle of stem death and root sprouting can occur many times in the life of an individual red oak. Many stems, for example, have root systems that are ten to fifteen years older than they are (Sander and Clark 1971)! This ability to vigorously and repeatedly re-sprout is an extremely important aspect in the ecology and survival of this tree species. Once a red oak acorn germinates (and less than one percent of acorns have an opportunity to do this!) and then has several years in which it can grow its root system (and very, very few seedling survive the first year or two of life), it then possess a remarkable degree of tenacity and persistence which, in spite of its slow rate of growth and in spite of all of the destructive things that can and probably will negatively impact upon it, enables it to survive and even come to dominate many potential types of forest ecosystems.

Photo by Kshera502, Wikimedia Commons

Red oaks can live up to 400 years and may reach impressive girths and heights. A famous, old red oak grows in the backyard of a house on Shelby Street in Frankfort, Kentucky. This tree is called the Shera-Blair Red Oak, and it has a circumference at breast height of 21 ft and a trunk that rises more than 40 feet before it branches. It has an estimated height of 130 feet.

Ninety-five percent of existing northern red oaks are sprouts (Sander 1990) These trees, especially in ecosystems under stress (like from fire, logging, deer browsing, disease, and insect defoliation (as from gypsy moths)), expand their influence with each passing stress event. Other, less well adapted and less vigorously sprouting tree species decline with each passing trauma while the red oaks persist and actually increase their numerical dominance. Red oaks are adapted to pass through these “ecological stress filters” much more readily than most of the other tree species in their forest community. So, over time, especially if some stressful agent is at work on the forests, the northern red oak will out compete and out survive most of their potential canopy competitors. Forked stems which are very common in northern red oaks (as seen in the picture below from a section of the Laurel Highlands Trail near the Route 30 crossing) are indicative of sprouts (Sander 1990).

Photo by D. Sillman

Back to our northern red oak on the ravine slope of the Nature Trail: the above ground tree is eighty years old, but the roots could be as closer to one hundred. The parental tree may have flowered a century ago and its germinating acorn and its seedling and sapling may have undergone extensive stress and destruction until, phoenix-like, this tall, straight stem finally persisted and “won” this section of the canopy.

In the fall, there are abundant acorns on the trail under this tree (and by spring almost all of them are gone, thanks, I am sure, to large, local populations of wild turkey and white-tailed deer!). There are many red oak seedlings growing under the cover of the raspberry and spice bush. There are fewer red oak saplings growing up above the shrub layer, but still enough to be easily noticed. Our tree, then, has survived and established itself as a major component of the evolving forest along our Nature Trail. I expect that, barring catastrophes, or maybe because of them, the offspring of our tree will increase in number and size over the coming decades and come to dominate this forest. We’ll check back in a hundred years or so to see!

References for Northern Red Oak:

Braun, E. Lucy. 1950. Deciduous forests of eastern North America. Blakiston, Philadelphia, PA. 596 p.

Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, D.C.

Little, Elbert L., Jr. 1979. Checklist of United States trees (native and naturalized). U.S. Department of Agriculture, Agriculture Handbook 541. Washington, DC. 375 pp

Marquis, D. A., P. L. Eckert, and B. A. Roach. 1976. Acorn weevils, rodents, and deer all contribute to oak regeneration difficulties in Pennsylvania. USDA Forest

Service, Research Paper NE-356. Northeastern Forest Experiment Station, Broomall, PA 5 p.

Sander, Ivan L. 1979. Regenerating oaks with the shelterwood system. In Proceedings, Regenerating Oaks in Upland Hardwood Forests. John S. Wright Forestry Conference. p. 54-60. Purdue University, West Lafayette, IN.

Sander, Ivan. 1990. Quercus rubra L. Northern Red Oak.  In, Burns, R. M. and B. H. Honkala (tech coord) “Silvics of North America: Volume 2, Hardwoods.” U.S. Department of Agriculture, Agriculture Handbook 654. Washington, D. C.877 p.

Sander, Ivan L., and F. Bryan Clark. 1971. Reproduction of upland hardwood forests in the Central States. U . S. Department of Agriculture, Agriculture Handbook 405.Washington, DC. 25 p.

Schopmeyer, C. S., tech. coord. 1974. Seeds of woody plants in the United States. U.S. Department of Agriculture, Agriculture Handbook 450. Washington, DC. 883 p.

Seidel, Kenneth W. 1972. Drought resistance and internal water balance of oak seedlings. Forest Science 18(l):34-4

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