Old Growth Forest, Larch Mountain. Public Domain.
(Click on the following link to listen to an audio version of this blog …. Old Growth Forests
(This essay was originally part of my now defunct Between Stones and Trees website)
“Old Growth Forests” (also called “virgin forests” or “primal forests”) include the forests of North America that were first observed by arriving Europeans in the sixteenth century. North America was “an ocean of woods” (Pownall 1776 (from Whitney 1994)) and was covered by “the greatest forest on the face of the earth” (Williams 1794). The east coast of the new continent presented a tall palisade of trees to the arriving settlers, who, slowly at first but then with ever increasing speed and determination, slipped through this outer wall and then took this vast forest apart tree by tree and acre by acre. The colonists and settlers gathered materials to meet their needs but also very intentionally re-shaped the “godless wilderness” into a form that better fit their fundamental philosophies and ideals.
The North American forests had never been cut by humans. Native people had used their limited technologies (like fire) to modify them, but primarily these forests were sculpted by internal processes like ecological succession and externally arriving, natural disturbances like fire, wind, insect pests and defoliators, cyclic droughts, and climate fluctuations.
Every standing tree is a miracle of luck and design. Every tree that lives long enough to reproduce has survived by fortuitous location, optimal physiology and sequences of blind serendipity. The razor’s edge upon which each individual organism is balanced must be recognized. Every influence no matter how small has the capacity to tip the fate of an individual organism in both positive (growth, survival, reproduction) and negative (inhibition, destruction, and death) directions. In a population, the laws of probability will cancel out the influences of the extremely random and the advantages of fortuitous genetics will be observed. Even incremental advantages in genetic and physiological “fitness” will be favored and conserved over time. But, for the individual, almost anything can happen.
Old Growth. Tionesta, PA. Photo by Nicholas T, Flickr
In a forest, in any ecosystem, all of these “battles” are occurring simultaneously. A slow, uniformitarian process of genetic selection is occurring right along with the sudden, random, calamitous riot of catastrophism. Optimal genetics will benefit the population, but will not help the individual unlucky enough to be crushed by a landslide or swept away in the funnel of a passing tornado.
The Old Growth forests of North America were flickering in these dynamics of individual catastrophes and population change. The “stable, end-product” of succession was neither terribly stable nor close to any sort of a natural end point.
What did these forests look like?
Flagg (1872) stated that Old Growth Forests all had a “universal dampness of the ground.” The soil surface in these forests was covered with a great abundance of leaf and woody litter that had accumulated steadily over the many years the forest has existed. These organic materials were undergoing a slow and steady physical and chemical transformation via fragmentation and decomposition. The litter layer was thick and stratified and had, at its lower interface with the upper layers of the mineral soil, a dense, dark layer of humus. The canopy of the forest shaded the forest floor which greatly slowed evaporation. The surface leaves of the litter layer were wet from rains that might have occurred weeks before, the underlying fragmenting and decomposing leaves were wet, the humus was wet, and the soil was wet. Huge volumes of rain water was stored in these organic layers. They acted like a great, ecological sponge that slowed initial surface water runoff, and then steadily released water in between rain storms into the system’s streams and runs. The wet, leafy mold and soil also provided moisture for continued plant growth even during prolonged periods of drought. The hydrological benefits of these intact forest soil systems were profound.
Old Growth (left) and Second Growth (right) . Photo by TJ Watt. Wikimedia Commons
A second growth forest (a forest that arises after an old growth forest is cut) “stands on drier foundation” (Flagg 1872). The thick, leaf litter/humus system is gone or significantly reduced because of the physical impacts of logging or subsequent direct exposure to sunlight (which accelerates organic decomposition and also dries the litter sufficiently to allow wind erosion). The forest floor is also directly exposed to rainfall (which causes both the physical disruption of the litter and soil surface and also accelerates its water transport and erosion). Water from incoming rains flow through the forest system at rates significantly greater than seen in the old growth system. These rains then fill the streams of the forest’s watershed more rapidly (and these streams flow into their larger and larger rivers of the watershed at rates and water volumes much greater than previously observed). Heavy rains, then, have a greater potential to cause floods down the river systems of the altered forests.
Also, the lack of water retention in the absent forest “sponge” removes an important water source for the streams and runs of the forest ecosystem. In an old growth ecosystem these streams continue to flow between rain storms because they are fed by the steady water release from the forest soil’s organic layers. In second growth ecosystems, these streams and runs dry up in between rain storms and cease to deliver appreciable water volumes to their larger, draining rivers.
Downed wood in Old Growth Forest. Photo by J. Knouse. Wikimedia Commons
Noah Webster (1790) (from Cronon, 1983) noted the connection of dried up streams and springs and floods in New England following destruction of the old growth forests (I have taken the liberty to put Mr. Webster’s spelling and syntax into more conventional forms):
“The amazing difference in the state of a cultivated and an uncultivated surface of the earth is demonstrated by the number of small streams of water which are dried up by clearing away forests. The quantity of water falling upon the surface may be the same, but when the land is covered with trees and leaves it retains the water. When it is cleared the water runs off suddenly into the large streams. It is for this reason that floods in the river have become larger, more frequent, sudden and destructive than they were formerly.”
An old growth forest also has many fallen trees within it. These trees, in the cool, shaded, moist environment of the forest floor are covered with moss and are slowly rotting away. These fallen trees, depending on the nutrient and moisture dynamics of the forest, may even be covered with growing plants including tree seedlings. In the maritime forests on the east coast barrier island of Assateague, for example, fallen, rotting trees lay on the very well drained (and therefore very dry), sandy soils and are important seed beds for the next generation of trees of the forest. These decaying “nurse trees” cause the seedlings to grow in straight lines and impose a very unexpected geometric order to the subsequent forest. Possibly this phenomenon was also observed in the well drained, outwash soils that favored old growth white pine in Western Pennsylvania.
Old Growth coastal forest. Photo by P. Davis. USFWS. Public Domain
Growing on the trees in an old growth forests are abundant epiphytes (plants that grow on other plants) and, especially in cooler climates, lichens. Lichens in particular, because of their very slow growth rates and very limited ability to disperse over appreciable distances, may be a particularly important sign of an old growth ecosystem. Fungi and their mushrooms would also thrive in the shady dampness of an old growth forest, but their prodigious ability to make spores and the distances these spores can travel in the wind may preclude their use as old growth indicators.
Thoreau (1864)(from Thompson, 2020) also noted the above features of primal forests.
“[The forest] has lost its wild, damp, and shaggy look; the countless fallen and decaying trees are gone, and consequently that thick coat of moss which lived on them is gone too. The earth is comparatively bare and smooth and dry.”
Old Growth hemlock. Photo by W. Hamilton
Old growth forests should also have, and this feature seems so obvious that it might not need to be mentioned, old, and, therefore, large, trees. But, not all of the trees in an old growth forest are necessarily old and large. Kalm (1772) observing a primal forest in eastern Pennsylvania observed that “there are very few tree of an uncommon age” and that many of these larger trees were in stages of rot and decay. Further, he noted, “several trees are likewise torn out with their roots by the power of the wind.”
Most of the trees in an old growth forest, then, were only proportional to their maximum ages and sizes. There were, though, always a few individual trees that either because of their particular genetic or physiological vigor or, and this is more likely, because of a perfect historical convergence of fortuitous events (or “non-events”) that attained the great age and great size possible for their species. These giants, though, are and were rare, and should be greatly cherished.
Hearts Content Scenic Area, PA. Photo by Nicholas T. Flickr
Finally, an old growth forest should have a dense and complex undergrowth layer of vegetation. This undergrowth should include the seedlings of the next generation, or iteration, of the forest. Parkman (1892) writing lyrically and, possibly under the intellectual influences of Darwin and Spencer, described the undergrowth of an old growth forest in New England as full of abundant seedlings “crowding, choking, and killing each other, perishing by the very abundance.”
So, old growth forests should be damp and have a thick litter and humus layer. They should be full of downed trees that are coated with mosses and lichens, and have at least some large, old standing trees well covered with epiphytes and lichens. They should also have a well developed layer of undergrowth vegetation in which seedlings of the next generation or form of the forest are densely found.
References:
Cronon, William. 1983. Changes in the land : Indians, colonists, and the ecology of New England. Hill and Wang. New York.
Flagg, W. 1872. The woods and byways of New England. Boston. J. R. Osgood and Company.
Kalm, P. (1772) 1972. Travels into North America. Translated by J. R. Forster. The Imprint Society. Barre, Mass.
Parkman, F. (1865-1892) 1983. France and England in North America. 2 volumes. Reprint. New York. Literary Classics of the United States, Inc.ouse
Thompson, L. (2020). What does an old forest look like? Vermont Land Trust. https://vlt.org/2020/05/07/what-does-an-old-forest-look-like/. (01/20/2023)
Whitney, G. G. 1994. From coastal wilderness to fruited plain : a history of environmental change in temperate North America, 1500 to the present . Cambridge University Press.
Williams, Samuel. 1794 The Natural and Civil History of Vermont. Isaiah Thomas and David Carlisle Jr., Walpole, New Hampshire.