ARIZONA'S NATURAL VEGETATION AND GRAZING GROUNDS

ARIZONA'S NATURAL VEGETATION and GRAZING

BY KENNETH W. PARKER-Southwestern Forest and Range Experiment Station Arizona is a land of contrasting vegetation varying from wide expanses of desert and sweeping grasslands to extensive woodlands and from mighty forests to Arctic-Alpine slopes above timberline. Covering all like a gigantic tapestry wherever Nature wishes it to grow is the grass. Upon this annuity of Nature and in many areas supplemented with valuable browse species has developed an important livestock industry.

Arizona's grazing grounds were undoubtedly first used by domestic livestock brought in with the founding of the early Spanish missions in the 17th Century. The Franciscan mission of Quebabi was established about 1687 in Santa Cruz County. A few years later and farther north, the Franciscan mission of Tumacacori, now sponsored as a National Monument, was established. Father Kino in his diary written in 1700 mentions the gathering of cattle, sheep, and horses from the missions near Tucson and sending these livestock to California. Due largely to Indian depredations these early missions did not flourish nor for the same reason did the later (1825-1863) Mexican land grants.

ing of cattle, sheep, and horses from the missions near Tucson and sending these livestock to California. Due largely to Indian depredations these early missions did not flourish nor for the same reason did the later (1825-1863) Mexican land grants.

The real development of the livestock industry in Arizona started in the Eighties with the construction of the transcontinental railroads and the subsidence of Indian wars. From that time on, development was rapid until today there are about 900,000 head of cattle and 890,000 sheep in the state. Sheep and cattle are commonly grazed in the central and northern parts of the State, whereas in southern Arizona cattle are grazed almost exclusively. Cattle are predominantly of the Hereford breed and sheep are principally Rambouillet with some crossings such as with the Hampshire and Suffolk breeds.

The diversity in natural vegetational com-munities is the result of wide variations in elevation, rainfall, temperature, length of growing season and soil. Elevations in the State range from 137 feet in the lower valley of the Colorado to well over 12,000 feet in the San Francisco Peaks. Rainfall, which has the greatest effect on the kind of vegetation, in general becomes greater with increase in elevation. The average annual rainfall varies from less than 3 inches in the desert region to about 35 inches in the mountain country. Length of growing season, which is based on the number of days occurring between the last killing frost in the spring and the first killing frost in the fall, varies from about 90 days in the higher mountains to well over 200 days in the lower elevations. Because of these major variations in climate, which are often found within relatively small areas, one may traverse in a day's time desert, covered largely with creosotebush or other typical desert shrub, and by increasing altitude, travel through areas covered largely with juniper, piñon, and grass. With further increase in altitude, the piñon-juniper country merges into ponderosa pine, and with still further increase in altitude, this belt of vegetation merges into quaking aspen, Douglas-fir, and white fir, which finally is displaced by spruce. Above the spruce belt, which usually forms timberline, particularly on the north slopes, trees are no longer found unless it is in the form of shrubby, gnarled vegetation, the plant cover being made up mostly of grasses and sedges. In this latter belt of vegetation rainfall is plentiful; however, plant development is limited by low temperatures and a short growing season. On the other hand, in the desert country moisture is the limiting factor. the grazing of livestock is likewise limitedeither by climate or the character and kind of vegetation. In each of these vegetational

GROUNDS

the grazing of livestock is likewise limitedeither by climate or the character and kind of vegetation. In each of these vegetational

Nearly nine hundred thousand sheep, principally Rambouillet with some crossings such as Hampshire and Suffolk breeds, roam Arizona ranges.

zones certain typical plants predominate to the extent that they lend to each plant com-munity a characteristic aspect.

Whenever the average person thinks of the Arizona desert he probably draws a mental picture of a landscape covered with either saguaro or cholla cactus. Actually, these plants, along with paloverde, are to be found on only about a fourth of the desert. Most plant scientists recognize two major divisions of desert vegetation in Arizona-the northern desert, which is confined to the northern borderlands, and the extensive southern desert which covers the southwestern third of the State. The northern desert is characterized by sagebrush and because of its relative in-accessibility is seldom seen by the traveler. The sagebrush desert is utilized primarily by sheep.

In the southern desert, precipitation varies each year from zero to about 10 inches. The low and erratic rainfall, combined with the low moisture content of the air produces a typical desert climate. Evaporation is extremely high and temperatures range from as low as 15 degrees in the winter to a sizzling 130 degrees in the summer. The southern desert shows great variation, ranging from the dark green creosotebush, yellowish-green palo-verde, giant cacti, and mesquite to the silvery bur-sages and encelias. Innumerable species of cholla and pricklypear may become locally abundant. Ironwood is frequently abundant wherever frost-free areas occur. Grasses are mostly annuals; however, two perennials commonly occur, especially wherever the site receives flood water. These are sacaton andbig galleta, the latter botanically interesting because it is a shrub. Annuals include six-weeks grama, needle grama, sixweeks three-awn, and during the late winter sixweeks fescue and Schismus barbatus, an annual grass introduced from the Mediterranean region of Europe. The water courses are generally characterized by benchlands and flood-flats covered with mesquite. Nichol recognizes in “Natural Vegetation of Arizona” (Univ. of Ariz. Tech. Bul. 68) three major subdivisions of the Southern Desert, namely, (1) paloverde cacti, (2) creosotebush-saltbush, and (3) mesquite bosques or bottomlands.

Two distinct growth periods occur for the annuals, a winter or early spring growth that begins as soon as temperatures permit and summer growth that starts whenever it rains. Two of the winter annuals, filaree (also of Mediterranean origin) and Indian wheat, in occasional years of plentiful rainfall form considerable amounts of valuable forage which is utilized as forage by both sheep and cattle. Most desert shrubs, with the exception of a few plants such as mesquite, ironwood, and salt-bushes, are either too leathery or thorny to be of value to livestock.

Many unusual and unique plants are to be found on the desert. The symmetrical, columnar saguaro and the night-blooming cereus or Reina de la Noche are well known. In the Kofa Mountains, well above the level of a once existent and prehistoric sea, are about 100 individuals of California palm. Along the Mexican border the candelabralike organ pipe cactus grows to a height of 10 to 20 feet, opening its beautiful pinkish blossoms after sunset.

The jumping cholla with its cruel spines is rapidly encroaching on many adjacent grassland areas, rendering more difficult and costly the gathering of cattle. The invigorating smell of creosotebush following a warm summer rain is unforgettable. This evergreen shrub, worthless as forage, characterizes thousands of square miles in the Southwest.

Above the desert are the extensive grass-lands, which with the woodlands and forested areas, form the most important grazing grounds. Annual rainfall is generally above 12 inches. Drought is intermittent and unpredict-able, but less frequent than in the desert. Un-like the parvenu forage plants of the desert, the vegetation usable by livestock comes al-most entirely from native perennial grasses, weeds, and browse. The bulk of the perennial grass growth is produced during the summer months. This occurrence permits the rancher through marketing the offspring and culled animals in the fall to adjust the numbers of animals in his herds in accordance with the size of the forage crop. Two major subdivisions are recognizable-desert grassland or mesquite grassland and short grass.

The desert grassland reaches its best development in southeastern Arizona. Wherever curly-mesquite is predominant, this vegetational community resembles in many respects the immemorial sod of the Great Plains. Although the principal growth season is in July and August, temperatures are such that growth is likely to occur whenever rain falls. Aside from curly-mesquite grass, blue, black, hairy, sprucetop, and Rothrock gramas occur in varying degrees of abundance and locally any one of these species may become dominant. All of these grasses provide highly nutritious and palatable forage. These qualities combined with the mild winters make the area admirably suited for the yearlong grazing of cattle.

As a whole the short-grass community comprises some of the best range land in the State. Grazing may be carried on year long, although in the northern parts it may be used in the spring, summer, and fall with the piñon-juniper woodland reserved for winter. The principal range forage is blue grama. Other common constituents of the short-grass plant community are black, hairy, and sideoats gramas, Texas-timothy, ringgrass (a worthless species), galleta grass, red threeawn, and alkali sacaton.

Chaparral vegetation, occasionally referred to as the elfin forest, is confined largely to central Arizona. The aspect of this plant community is due to shrubs and trees which are also its principal components. There is considerable variation in the floristic composition which varies from one or two plant species to a heterogeneous mixture of several. Among the more commonly occurring plants are: turbinella oak, manzanita, desert ceanothus, squawbush, mountain laurel, Apache-plume, mountain-mahogany, buckthorn, catclaw, silk-tassel, coffeeberry or jojoba, algerita, and juniper. The Arizona mohair industry is largely centered in the chaparral country. Over 200 thousand goats are supported mainly on the many browse plants previously mentioned. The woodland phase is found in southern Arizona and is composed mainly of emory, gray, and Arizona white oaks. Both the chaparral and oak woodland plant communities rangefrom 4,000 to 6,000 feet in elevation, with rain fall varying from 12 to 20 inches per year. In many respects it is similar climatically to the piñon-juniper community and most of the grass species found in the latter occur as an undercover in the chaparral and oak woodland areas.

Here the plant community is composed chiefly of piñon and juniper together with a few evergreen oaks. Elevation ranges from 5,000 to 7,500 feet with annual precipitation varying from 12 to 15 inches. Where the stand of woodland is open enough to permit it, the ground cover is composed principally of grasses, including blue grama, galleta grass, Texas-timothy, sideoats, hairy, and black gramas, muhly grasses, and such browse species as saltbushes, beargrass, and mountainmahogany. Grazing may be year long but years occur when death losses from severe winter conditions are heavy.

Spreading in a tremendous crescent across northeastern Arizona lies a mighty forest. Approximately all lands above 7,000 feet are included. Rainfall varies from 15 to 35 inches or more annually. The frost-free growing season decreases markedly with increase in altitude, so that in the small areas above timberline (about 11,000 feet), it is less than 90 days. Beginning at 7,000 feet elevation, ponderosa pine is the common timber species up to about 9,000 feet, where it gives way to Douglas-fir, white fir, and quaking aspen which extend on up to about 10,500 feet. This zone of plant life is most colorful in the fall when the leaves of the gambel oak turn red and the aspen becomes yellow, with the first frosts. Here, too, is also to be found the interesting cork-bark fir. In the higher elevations Engelmann spruce becomes predominant, particularly on north exposures. The forest areas because of climatic conditions are used for grazing only during the summer and early fall months. In the lower elevations blue grama is the predominant species, but in most areas above 8,000 feet Arizona fescue, mountain muhly, pine dropseed, and western bluestem are the principal forage grasses.

Even the most barren and forbidding parts of the desert, in occasional years of plentiful moisture, can become a riot of color as well as abundantly covered with lush forage which for a few short months would seem capable of supporting unlimited numbers of livestock. Unfortunately, however, years of plenty are infrequent even in the higher grasslands and forested areas. Wherever the number of livestock on the grazing grounds have been figured on the basis of the most favorable years, catastrophe to the ranching enterprise results during the drier years because of shortage of forage. The key to successful ranching and to the maintenance of productive vegetation for grazing grounds lies in grazing moderate numbers of animals. Moderate grazing recognizes the living requirements of the vegetation by leaving about half the forage on the ground at the end of the grazing season. Such proper use of the grazing grounds thus prevents the grass tapestry and other grazable vegetation from becoming thin and worn or replaced with noxious range plants and Nature responds through increased amounts of forage and healthy, productive livestock.