UNITED STATES DEPARTMENT OF AGRICULTURE

DEPARTMENT BULLETIN No. 1405

Washington, D. C.

September, 1926

GRAZING PERIODS AND FORAGE PRODUCTION ON THE NATIONAL FORESTS

By ARTHUR W. SAMPSON, Plant Ecologist, and HARRY E. MALMSTEN, Grazing Examiner United States Forest Service

Stockmen in the West have always had confidence in the adequacy of the native forage crop to provide pasturage for their livestock. Indeed, under normal climatic conditions this enormous natural resource has not failed the grazier, except where it has been called upon to meet unreasonable demands. The productivity of the range has declined sharply, however, wherever the requirements of plant growth have been disregarded for many years in succession. Where there has been too early or too frequent and to heavy grazing, undue trampling, or some other unsatisfactory feature of range use, the results have been uniformly bad. Many conspicuous examples show that abundant nutritious forage can not be expected in the absence. of rational grazing and livestock management.

More and better forage, as well as the maximum production of beef, wool, and mutton, is a primary object of grazing management. To maintain the forage productivity of a range unit it is necessary

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to be able to determine (1) when the range is ready for grazing, (2) the degree, or intensity, and frequency of grazing that may be allowed, (3) how to handle the stock in order to begin at the right time and to regulate intensity and frequency of grazing, and (4) the natural revegetation of the range that may be relied on in making plans for handling the stock. How this may be done is indicated in this bulletin on the basis of observations made over an extensive region, but particularly at the Great Basin Experiment Station and in other parts of the Wasatch Mountains of Utah.

MAJOR FORAGE TYPES OF THE WASATCH MOUNTAINS

The forage cover in the major portion of the Wasatch Mountain Range may be classified into three major types or zones, the boundaries of which are largely determined by climate. These types are designated according to the characteristic tree species, as oak-brush, aspen-fir, and spruce-fir.

OAK-BRUSH TYPE

The oak-brush type, the lowest of the three, occurs between elevations of about 6,500 and 8,000 feet, or in what is often termed "the foothills." Limited rainfall and comparatively high temperatures are characteristic. The brush species are often comparatively dense, the perennial herbaceous species ordinarily occurring in a scattered stand as an understory of the brush, partly as a result of too early grazing and of overgrazing in the past.

Gambel oak (Quercus gambelii) predominates throughout this type. The principal browse species associated with it are snowberry (Symphoricarpos oreophilus), sagebrush (Artemisia tridentata), service berry (Amelanchier alnifolia), birch-leaf mahogany (Cerocarpus montanus), chokecherry (Prunus demissa), squaw apple (Peraphyllum ramosissimum), and bitter brush (Purshia tridentata). The principal herbaceous vegetation is composed of one or more species of the following genera: Blue grasses (Poa), wheat grasses (Agropyron), fescues (Festuca), needle grasses (Stipa), mountain rice (Oryzopsis hymenoides), June grass (Koeleria cristata), butterweed (Senecio), bluebell (Mertensia), and yarrow (Achillea lanulosa).

ASPEN-FIR TYPE

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The aspen-fir type is highly valuable for grazing. It lies between elevations of about 7,500 and 9,500 feet, the lower boundary adjoining the oak-brush type and the upper merging into the spruce-fir type. Aspen (Populus tremuloides) occurs over extensive areas, and where overgrazing has not destroyed the forage the aspen type supports a dense stand of valuable plants. Douglas fir (Pseudotsuga taxifolia) and white fir (Abies concolor) occur as individual scattered trees in the aspen type and on rather steep north exposures join with Engelmann spruce (Picea engelmannii) and Colorado spruce (P. pungens) to form small areas of a distinct timber type

1 Tidestrom maintains that the western aspen is a distinct species, and employs the name Populus aurea therefor.

which support but a sparse stand of forage. Small openings also occur throughout the zone, but they are ordinarily in a depleted condition from past abuse and now support a stand largely of annuals and unpalatable perennials.

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Of the browse plants, snowberry clearly predominates throughout the aspen-fir type. The principal associated woody species are chokecherry, service berry, elderberry (Sambucus), wild (Rosa), spine currant (Ribes montigenum), honeysuckle (Lonicera), and manzanita (Arctostaphylos). The herbaceous vegetation consists chiefly of various species of brome grass (Bromus), wheat grass, blue grass, spiked trisetum (Trisetum spicatum), pine grass (Calamagrostis), wild geranium (Geranium), vetch (Vicia), lupine (Lupinus), bluebell, butterweed, pea vine (Lathyrus), niggerhead (Rudbeckia occidentalis), dandelion (Leontodon taraxacum), beardtongue (Pentstemon), sweet-cicely (Osmorrhiza), yarrow, sneezeweed (Helenium hoopesii), tall larkspur (Delphinium), meadow rue (Thalictrum fendleri), death camas (Zygadenus), and Indian paintbrush (Castilleja).

SPRUCE-FIR TYPE

The spruce-fir type occupies the high plateaus at elevations ordinarily above 9,000 feet. Engelmann spruce and alpine fir (Abies lasiocarpa) form dense stands on north exposures and other favorable sites and also occur as small clusters over the whole area. The bulk of the type is open and supports a cover that is chiefly herbaceous, with here and there an admixture of browse. Because of the high quality of the forage, the abundant water, and the moderate summer temperatures, the type embraces the best summer range in the Wasatch Mountains. The cover of greatest value for grazing, especially in the open parks, consists largely of grasses and other herbaceous plants, with considerable browse in the timbered lands. In the nineties and the early part of the twentieth century overgrazing was excessive here, and extensive areas are still in a badly depleted condition. Untimbered areas which were not seriously injured in the past, and on which the forage has had a chance to recover fully, support a dense stand of very valuable grasses and other forage plants.

The herbaceous vegetation is composed chiefly of species of wheat grass, needle grass, sedge (Carex), brome grass, blue grass, pine grass, meadow barley (Hordeum), sweet sagebrush (Artemisia), blue beardtongue, yarrow, bluebell, dandelion, mountain dandelion (Agoseris), tall and low larkspur, death camas (Zygadenus), lupine, aster (Aster), butterweed, cinquefoil (Potentilla), Mexican dock (Rumex), and knotweed (Polygonum). The most important browse plants are spine currant, elderberry (Sambucus), rabbitbrush (Chrysothamnus), willow (Salix), wild raspberry (Rubus), and sagebrush (Artemisia tridentata).

CLIMATIC FACTORS IN RELATION TO GRAZING PERIODS

Careful meteorological records have been kept since 1914 in each. of the three major types on the Ephraim Canyon watershed, the oak-brush at 7,100 feet elevation, the aspen-fir at 8,700 feet, and the

spruce-fir at 10,000 feet. Such factors as air temperature, soil temperature, precipitation, air humidity, evaporation, wind velocity, and sunshine duration and intensity all directly or indirectly affect plant growth, but those most closely related to the grazing periods are air temperature and precipitation. Air-temperature records were obtained by using thermographs and maximum and minimum thermometers exposed in shelters 412 feet above the ground. Precipitation was measured in standard rain gauges.

AIR TEMPERATURE

The records show temperature characteristics typical of mountain regions and clearly indicate the effect of elevation. The highest

FIG. 1. Typical thermographic records in the first half of June, 1922, showing the relation of temperatures and the differences in the daily range

maximum temperature and the widest daily variation are found in the lowest type; with increase in altitude there is a slow decrease in the minimum temperature and a larger decrease in the maximum, which is responsible for the flattening of the daily temperature curve for the spruce-fir type, as shown in Figure 1. Mean temperatures accordingly diminish regularly with increased elevation. During the main growing season, from June to September, inclusive, the mean-temperature decrease gradient for every 1,000 feet difference in elevation is 4.05° F. from the oak-brush to the spruce-fir type, 3.91° from the oak-brush to the aspen-fir type, and 4.23° from the aspen-fir to the spruce-fir type. The meantemperature decrease gradient for the year is somewhat similar to that for the growing season, although owing to temperature inversions in winter the exact rates of decrease are somewhat different.

TABLE 1.-Average temperature (in hours) above and below 40° F., and number of hours freezing, period 1914 to 1922, inclusive

By reference to Table 1 and Figure 2, it will be seen that freezing temperatures did not occur during the period considered in any

FIG. 2.-Average monthly temperature (in hours) above 40° F. and below 32° F. (Period 1914-1922, inclusive.) Temperatures above 40° F. are favorable for plant growth, while freezing temperatures are detrimental. During the main growing season the hours of favorable growing temperatures are at a maximum and the hours of freezing temperatures are at a minimum number

of the zones during July and August, but that in June and September, the other two months of the main growing season, they occurred with considerably frequency in the upper zone and are not absent even from the oak-brush zone. Still more striking is the decrease in the number of hours above 40° 2 in the spruce-fir

Investigations conducted by various workers indicate that at or below 40° F. little or 20 growth takes place in plants of the character of those which furnish forage in the Wasatch Mountains.