World famous are the graceful white-barked Quaking Aspen1 trees on the north rim of the Grand Canyon, and justly so, especially when seen clothed in their brilliant autumn colors. Yet, if in passing one pauses but a moment, he might detect an almost imperceptible minor undertone in what is otherwise a glorious symphony of the forest. Among the aspen on the north rim there is very little reproduction at present. This situation in combination with certain biotic factors does not promise a very prosperous future for the aspen in the Grand Canyon National Park.
The aspen, a sub-climax species in our forest on the north rim, is just one of several steps of plant succession in the natural reforestation of burnt over areas in this region. The presence of aspen trees in such great numbers on the north rim, where it seems to be an indicator of former forest fires, bears witness to the extent of the early fires in this region. That there were such forest fires is a fact which is supported by statements of some of the "old timers" in Southern Utah, the country a little to the north of the north rim. Nate Adams, one of these early pioneers still living in Kanab, in southeastern Utah, tells how in the pioneer days of this community, the inhabitants would frequently look to the south to see great clouds of smoke rolling over the Kaibab Plateau on the north rim of the Grand Canyon. This smoke would be almost continuous from early spring until late autumn.2 Because white men were still being killed by outlaw Indians in that day,3 very few if any trips were made up into this Kaibab Country. Hence they knew little more about these fires than just what could be observed from a distance. It is supposed, nevertheless, that many of these fires were caused by lightning, for that is still the case today. In the absence of any protective measures, these fires ran their course and probably destroyed extensive areas of timber. In addition to these forest fires from natural causes, we hear tales about the Indians chasing their prey out on the points on the rim of the canyon and then setting fire to the forest behind them to concentrate the game at the very tips.4
Almost anywhere in the north rim forest will be found the remains of old charred stumps standing today like snaggled teeth among the otherwise healthy growth of timber. These stumps stand as mute evidence to the fact that much of the plateau had been burned over at one time or another, possibly even more than once. Everywhere that the ground was swept clean by such fires, this made way for a series of changes which eventually made possible the present beautiful stands of Quaking Aspen in the Kaibab Forest. Much of this took place in the days before this area was made a national reserve or a national forest.
Today, now that modern methods of fire protection are maintained in this forest by both the National Park Service and the National Forest Service, the number of fires and the extent of the areas destroyed by them, have been reduced to a negligible quantity. Under this present influence, there is a greater chance for natural reforestation to progress along lines of normal development. This involves an interesting plant succession which obviously has been in progress for some time. With fewer interruptions by forest fires, this succession will normally proceed to a climax vegetation. The aspen is not a climax but a subclimax tree in this forest. It is obvious that at best it can be considered but a temporary tree. In the changes which are bound to occur in this plant succession, it is evident that the aspen will finally decrease as the climax evergreens crowd it out.5 Many evidences that this is now in progress on the north rim can be found. If this continues the aspen no longer will form a conspicuous part of the forest formation in this region. This would normally take a very considerable period of time dependent, for the most part, upon the rapidity of the growth of evergreens.
There is, however, a biotic factor involved, which will doubtlessly hasten the reduction of the number of aspen trees on the north rim. Deer are very fond of aspen leaves. Anywhere an aspen seedling appears, very soon there is a deer on hand to chew it up. That this has effectively limited aspen reproduction, is an inescapable fact as one looks through the forest to see practically no new, young growth. Incidentally this fondness of the deer for aspen shoots and leaves explains the striking uniformity of the height of the lower branches of these trees throughout the forest. The deer eat off not only all the leaves but also all the tender new shoots as far up the tree as they can reach.
In marked contrast to this general condition through the Kaibab Forest, one finds rather extensive reproduction of the aspen in the vicinity of the Quaking Aspen Ranger Station, of Forest Service in Kaibab Forest just north of the park boundary. Here a number of hounds are kept and, of course, no deer come near. Thus the aspen are protected and normal reproduction thrives.
In addition to this general absence of reproduction among the aspen, is also to be considered the age of these trees now growing today. Very few individuals are under twenty years of age, while the general run probably will vary somewhere between twenty-five and sixty years old. The aspen is normally a short-lived tree.6 A considerable number of these trees in the forest today are now beginning to show signs of old age. It might safely be concluded that, the present conditions maintaining, there will be a great deduction in the number of aspen trees to be found on the north rim within an estimated period of from about fifty to seventy-five years. The aspen may conceivably even approach a situation of comparative rarity in this region eventually, present conditions maintaining.
It is evident that the rate of reduction of the number of aspen trees on the north rim will be retarded should there be any decided reduction in the size of the deer herd in this region. If this does take place, then reproduction will thrive and the aspen will grow normally in its role as a subclimax tree until finally crowded out by the climax spruces,7 pines, firs,8 and Douglas Firs,9 or "False Hemlocks."10 Under any circumstances, however, as far as the writer can see, except for the abandoning of protective measures, the Quaking Aspen trees in the Kaibab Forest on the north rim of Grand Canyon, must eventually be reduced to a relatively limited number of individuals at the most.
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