By A. R. Croft, Ranger Naturalist.
SOME very interesting aspects of natural reforestation after burns in pinyon-juniper forests may be observed in the Grand Canyon National Park, near Grand Canyon village.
Upon visiting burns in great lumber producing forests one is impressed, first, with the direct losses such as the destruction of potential lumber, property damage, and loss of life, and second, the indirect losses, not measurable in monetary terms, such as damage to soil, watershed, grazing, game cover, and recreation.
It is of course true that both of these classes of loss by fire appear to some extent in forests of the pinyon-juniper type such as occur at Grand Canyon, but on these burned areas the author has been impressed most by the apparent great length of time required to re-establish a normal forest. This length of time has been approximated by a study of the plant cover on two burns of known age, and by age determinations of the normal forest of the region.
The youngest burn in the South Rim region, a crown fire, occurred in 1929. Its location, which may be called Area One, was a short distance south of Yaki Point, just off the main highway. In an article in the October number of "Grand Canyon Nature Notes" the author pointed out that the plants in this area could be placed in two groups. The first consisted of those which had grown in a suppressed condition on the forest floor, the roots of which had not been killed by fire. Group two consisted of plants which had migrated to the site since the burn. As might be expected, not a single seedling of the trees constituting the former climax forest could be found, even though adjacent trees had apparently matured seed every year since the burn.
Let us now consider another burn of known age, one about thirty years old, located between Grand Canyon village and Yaki Point, which is designated as Area Two. Thirty years after the climax forest was destroyed the principal plants on the site are as follows:
There are also a few scattered pinyons and junipers on this area which may be classified as follows: (1) Mature trees which escaped death at the time of the fire, (2) A few young trees, which as seedlings at the time of the fire, escaped its ravages, and (3) A very few young seedlings which have been established since the burn. This last group is practically negligible.
In the absence of older burns of known age in the vicinity, which which this interesting evolution of the pinyon-juniper forest could be traced, it was necessary to jump a great intervening gap, between Area Two stand and maturity, and determine the age of an average normal stand. Such a determination gave the approximate lapsed time between the beginning of a reproduction on Area Two and the mature forest. For this purpose advantage was taken of a condition on Area One. A salvage cutting for fuel was being made so it was comparatively simple to determine the age of a normal mature forest by counting the rings on the newly sawed stumps.
The results of the counts are shown in the accompanying figure. It must be remembered, however, that these curves show only the history of the individual trees, not the history of the forest. The trees represented in the curves constitute only one of many groups which have occupied this same site.
Reference to the curves shows that the junipers considered, started growth in 1620, about the time the Pilgrims landed at Plymouth. In 1929, when they were killed by fire, they had been alive about three hundred years and were still growing well. Three pinyon trees, which grew nearby, commenced growth about fifty years later and were approximately two hundred and sixty years old at death. The yellow pines commenced growth about one hundred years after the junipers and were their neighbors in the forest for approximately two hundred years.
If we may apply these calculations in a rough way to growth on burns in this region after reproduction starts, where conditions are about the same, it is possible to arrive at the approximate time neccesary for nature to reforest a burned area on harsh sites such as exist on the South Rim of the Grand Canyon.
Recapitulating, we find one area with no reproduction three years after burning, another area with reproduction practically negligible thirty years after burning. Here we may safely assume that fifty to seventy-five years may be necessary to secure a fairly well stocked area. Studying a mature forest, we find its age to be about three hundred years.
It we review the limited data at hand, it is safe to assume that about three hundred and fifty years may be required for nature to repair the damage done by fire in a few hours in a climax forest of the pinyon-juniper type, such as occurs on the South Rim of Grand Canyon. In view of this apparent fact, and in view of the fact that over eighty percent of the forest fires in the United States are man caused should we not re-dedicate ourselves to the task of spreading the gospel with renewed vigor, which is so well stated by the common motto:
"BE CAREFUL WITH FIRE"
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