PINON-JUNIPER FORESTS

By W. Ward Yeager,
Associate Forester.

The forest of the semi-arid Southwest is composed primarily of only two trees, pinon pine (Pinus edulis) and Utah juniper (Juniperus utahensis). In some parts of the forest the Pinus edulis is replaced by Pinus cembroides or Pinus monophylla, and the Utah juniper is replaced by Juniperus monosperma (one-seeded juniper) or Juniperus pachyphloea (alligator bark juniper). This change of species does not change the general character of the forest, but it does increase the range of the forest type. The pinon-juniper forest is the typical forest cover of the semi-arid portions of Arizona, New Mexico, southwestern Colorado, southern Utah, and southern Nevada. Within this range its occurrence is determined by elevation and precipitation. The usual elevation of occurrence is between 4,000 and 8,000 feet above sea level. On the lower fringe of the range where temperatures are high and precipitation low, the forest is associated with desert vegetation. On the high limits of the range where lower temperatures and higher precipation are suitable, the associated forest cover is composed primarily of yellow pine (Pinus ponderosa). Within the extreme range limits are extensive pure stands of pinon-juniper.

The individual trees of the forest are short and much branched with a dense low crown. Seldom do the trees exceed a height of thirty feet or a diameter of two foot. The stand is most dense in the upper elevation limits. At Mesa Verde National Park, in Colorado, there are about 730 trees to the acre, pinon pine making up about two-thirds of the number, and juniper one-third. In the lower range limits where the juniper predominates, the number may drop to 200 trees per acre. Such a forest is dwarfed by comparison with other pine forests of the West, and for this reason there is some tendency to ignore its forest character. When compared to adjacent desert vegetation of the lower elevations, the pinon-juniper attains its rightful place in the scheme of nature.

To commerce and the lumber industry, pinon and juniper are of low values because at best they can furnish only fence posts and fuel wood for local comsumption. The pinon nuts, or seeds, have a certain relative value as food for the Indians and Mexicans who live within the forest, but the commercial possiblities have been developed only slightly, Within our national parks and monuments we are not concerned with commercial aspects but rather with recreation and conservation values. This forest protects a great proportion of the Southwest from excessive wind and water erosion, and improves the recreational attractiveness of all areas where it occurs.

The development of parks often has a far-reaching influence on the forests of our high-use areas -- an influence that is more pronounced in a pinon-juniper forest. The delicate balance of nature which permits this forest to grow is so fine that extreme caution must be used in making adjustments. Minor changes in drainage and exposure caused by construction of roads, parking areas, sewer lines, water lines, etc., may so reduce the vitality ef existing trees that they succumb to insect and disease attack, and are broken or uprooted by wind. The pinon can rarely readjust itself to physical changes or abuse. The juniper, on the other hand, is able to do so. Along a trench or bank slope a third of the roots of a pinon may be cut off, and the pinon will usually die. Under similar conditions some of the branches of a junipter will die and some will live. Thus the crown balances the roots and life continues. Pinon grows comparatively rapidly, and dies young (200 years). After death, it quickly disintegrates. The juniper grows slowly, lives for centuries, and after death may remain standing for fifty years. It is slow to deteriorate even when actually in contact with the soil. Where this forest type is subject to physical abuse, we must expect tree loss. Major control projects of Ips species in pinon pine have been carried out in Mesa Verde and Grand Canyon National Parks, where the insect condition now appears endemic. Insect loss is a normal condition and our aim is only to prevent the abnormal.

The tree loss from human influence, and from insects and disease, is far overshadowed by fire, even though fire occurrence in the Southwest is comparatively low. Man-caused fires are exceedingly few, but they usually occur in areas of high use where individual tree values are great. Lightning fires are not numerous compared to the Northwest where one lightning storm has been known to start 96 fires within a national forest. It was not intended that the pinon-juniper forest should burn over and no provision was made by Nature for natural reforestation.

Neither pinon nor juniper can reestablish itself by root sprouts or coppice. All seeds are readily burned in any hot fire. Pinon produces an abundant seed crop only once in five to seven years. The juniper produces only one seed to the berry, and a small percentage of each year's seed is viable. Rodents destroy most of the seeds produced in normal years. The seed of either species is too large to be scattered over a burned area by wind. Neither birds nor rodents scatter seed into a burned area, except on a narrow strip around the margin. Natural reforestation of a burn is negligible. Artificial reforestation is slow and expensive.

Because fires are controlled while small, and occurrence is infrequent, no spectacular display is before the public to make the people conscious of the fire danger. The 4500-acre fire which occurred on the west boundary of Mesa Verde National Park in 1934 furnished convincing proof that a pinon-juniper forest can burn with a vengeance. The fire occurred when the thermometer registered 102, the humidity was below 8 per cent, and a strong wind was blowing from the southwest. These conditions are not uncommon. The fire burned every living thing within its perimeter. Heat was so intense that the sandstone rocks on the surface were burned until they flaked off to a depth of an inch, and soil retained no humus in the upper four inches. The first season following the fire, wind and water erosion was excessive. Now, five years later, only annual plants and shrubs which can sprout from their roots, make up the ground cover. No pinon or juniper exists within the area to reestablish a forest cover. Artificial reforestation is being attempted, but the process is slow.

The very fact that fires do not occur frequently adds to the problems of protection because personnel organization is difficult to maintain, and experienced fire bosses are not to be had locally. The Grand Canyon National Park has enough fires each year to keep fire fighting personnel trained and experienced, but the majority of Southwestern park areas have so few fires and, in some cases, such a small personnel that, should a forest fire occur either in or near the park and not be confined to a small area, a disaster could occur which would destroy for generations the forest cover of the entire area. This potential disaster occasionally causes adequate fire protection to appear unreasonably high, but we must, if we are to protect that which is entrusted to us, prepare for the fire which we hope will never occur.

Golden eagles that are so large they have been captured by lassos thrown by cowboys are reported from the Mexican section along the Rio Grande included in the proposed Big Bend International Park of Texas and Mexico.

The golden eagle, common in Mexico, southern Texas, and New Mexico, sometimes attains a wingspread in excess of seven feet. It feeds largely on jackrabbits, ground squirrels, and carcasses of animals.

Occasionally, according to reports the National Park Service has received from Mexico, one of these large birds is roped by a cowboy who, after allowing the eagle to gorge itself on an animal carcass, suddenly comes from under cover to run down the confused bird, which can take to the air only with the greatest effort.

This practice would be illegal after establishment of the park because national parks in Mexico, as in the United. States, are sanctuaries for wildlife.