Landscape development, forest fires, and wilderness management.Science. 1974 Nov 08; 186(4163):487-95.Sci
Both the landforms and the vegetation of the earth develop to states that are maintained in dynamic equilibrium. Short-term equilibrium of a hillslope or river valley results from intersection between erosional and depositional tendencies, controlled by gravitational force and the efficiency of the transporting medium. Long-term equilibrium of major landforms depends on crustal uplift and the resistance of the rock to weathering. In most parts of the world landscape evolves toward a peneplain, but the reduction rate approaches zero as the cycle progresses, and the counteracting force of crustal uplift intercedes before the end form is reached. Davis described this theoretical model in elegant terms. Leopold and Hack have provided a new and quantitative understanding of short-range geomorphic interactions that tend to discredit the Davisian model in the eyes of many. However, the substitute models of quasi-equilibrium or dynamic equilibrium merely describe short-range situations in which this or that Davisian stage is maintained despite uplift or downwasting. Given crustal stability and an unchanging climate, landforms would presumably still evolve through Davisian stages. However, the Davis model cannot be tested, for despite tremendous inventions in geochronology and impressive advances in stratigraphic knowledge, we cannot yet establish the rates or even the fact of crustal uplift in most areas. We are left with an unresolvable problem, for the sedimentary records of erosional history are largely inaccessible, undatable, and indecipherable, at least in the detail necessary to describe long-term evolution of the landscape. We know more about the evolution and maintenance of vegetation assemblages than about landform evolution, for even long-term vegetation sequences are within the scope of radiocarbon dating, and the biostratigraphic record is detailed. Even here, however, distinctions between short-term and long-term situations must be made, so that Clements' grand scheme of vegetational climax-created soon after Davis's model of landform development-can be evaluated in terms of modern knowledge. Disillusion with the climax model paralleled disillusion with Davis's model in the 1950's, but the climax model can be tested, because the record of vegetational history is accessible, datable, and decipherable. In the short term of a few decades, successional vegetation stages occur in variety of situations, as confirmed by observation or by techniques such as tree-ring analysis. The successional vegetation stages are reactions to nutrients, weather, competition, and consumption. Such succession implies long-term disequilibrium, or at least unidirectional development. The long-term controlling factor in Clements' model of vegetation development is climate. With climatic stability the succession will proceed to a climax. In the Appalachian Mountains, geomorphic, microclimatic, and edaphic conditions limit climax development, producing a polyclimax, which is generally sustained by the dominance of these factors. Death and regeneration of single forest trees is controlled mostly by windstorms. The distributional pattern may be locally transected by lightning fires, major windstorms, or washouts. However, the long-term stability of Appalachian forests is demonstrated by pollen stratigraphy. Although we can infer the long-term stability of Appalachian forests, the trends and mechanics of short-term vegetational succession are not fully understood, because lack of sizable areas of virgin forest limits investigations of natural conditions. In this respect, the eastern United States is already much like western Europe, where climatic and disturbance factors in vegetational history cannot be disentangled. In the Great Lakes region, a large area of virgin forest exists in the BWCA of northeastern Minnesota. Here short- and long-term studies show that for at least 9000 years the principal stabilizing factor has been the frequent occurrence of fire. Major fires occur so often that the vegetation pattern is a record of fire history. All elements in the forest mosaic are in various stages of postfire succession, with only a few approaching climax. Fire interrupts the successful sequence toward climax. Geomorphic and edaphic factors in vegetational distribution are largely submerged by the fire regime, except for bog and other lowland vegetation. Fire recycles nutrients and renews succession. Nevertheless, despite the fire regime, the resulting long-term equilibrium of the forest mosaic, characterized by severe and irregular fluctuations of individual elements, reflects regional climate. In the BWCA and the western mountains, large virgin forests can be preserved for study and wilderness recreation. These wilderness areas must be managed to return them to the natural equilibrium which has been disturbed by 50 to 70 years of fire suppression. The goal should be to maintain virgin forests as primeval wilderness. This can be done by management that permits fire and other natural processes to determine the forest mosaic. Mechanized tree-felling and other human disturbances should be kept to an absolute minimum. Natural landforms also should be preserved for study and for certain nondestructive recreational activities. It is somewhat late for the Colorado River and other rivers of the West, because natural balances are upset by drainagebasin disturbances. Modification of plant cover on hillslopes changes infiltration and erosion rates and thus the stream discharge and sediment load, so the stream balance is altered from primeval conditions. Scenic Rivers legislation should thus be used to restore certain river systems and their drainage basins. Mountain meadows, badlands, desert plains, and patterned permafrost terrain are extremely fragile and sensitive. Intricate stream and weathering processes leave patterns easily obliterated by mechanized vehicles. Tire tracks can last for decades or centuries. The mineral patina or lichen cover on desert or alpine rocks are records of long stability, and slight differences in their development record the relative ages of landforms, to the year in the case of lichens. Delicate color differences in a talus slope or desert fan show long-term effects just as does the arboreal vegetation mosaic in another climatic setting. Preservation of virgin wilderness for study is viewed by some as a selfish goal of scientists, to be achieved at the expense of commercial and recreational development. However, scientific study and nonmechanized recreational uses are compatible in wilderness areas. Furthermore, the public does appreciate intellectual stimulation from natural history, as witnessed by massive support for conservation, the Wilderness Act, and a dozen magazines like National Geographic. Finally, no knowledgeable American today is unaware that ecological insights are necessary to preserve the national heritage. Western dust bowls, deforested slopes, gullied fields, silted rivers, strip mine waste-lands, and the like might have been avoided had long-term problems been balanced against short-term profits. Many economic questions cannot be answered intelligently without detailed knowledge of extensive virgin ecosystems. Long-term values are enhanced by those uses of natural resources that are compatible with the preservation of natural ecosystems. Esthetically, virgin wilderness produced by nature is comparable to an original work of art produced by man. One deserves preservation as much as the other, and a copy of nature has as little value to the scientist or discerning layman as a reproduction of a painting has to an art scholar or an art collector. Nature deserves its own display, not just in tiny refuges but in major landscapes. Man is only one of literally countless species on the earth. Man developed for a million years in a world ecosystem that he is now in danger of destroying for short-term benefits. For his long-term survival and as an expression of his rationality and morality, he should nurture natural ecosystems. Some people believe that human love of nature is self-protective. For many it is the basis of natural religion. The opposition of many Americans to the Alaska pipeline is a manifestation of almost religious feeling; most never expect to see the Alaskan wilderness, but they are heartened to realize that it exists and is protected. The same can be said of those who contribute to save the redwoods in California. Here cost analysis fails to account for the enormous value people place on nature and on the idea of nature as contrasted to the private gain of a few developers. Americans admire European preservation of works of art. Europeans admire American foresight in setting aside national parks. However, the distribution of protected natural areas in America is uneven and inadequate, and vast areas continue to be developed or badly managed despite widespread new knowledge about long-term human interest in wilderness preservation. Darwin turned nature study into the study of natural history. He could observe natural features in vast undisturbed areas with no thought that human interference had been a factor in their development. Today such natural landscapes have practically vanished. Those that remain should be preserved as extensively as possible, and managed with scientific knowledge of the natural processes that brought them to being. At the present accelerating rate of exploitation, massive disturbance, and unscientific management, soon no natural areas will be left for research or wilderness recreation. Some say that scientific curiosity and the ability for recreation define man. This is reason enough for wilderness preservation. However, a more ominous conclusion that the survival of man may depend on what can be learned from the study of extensive natural ecosystems.