Effects of Thirty Years of Protection from Grazing in Desert Grassland

Abstract

It has long been recognized that areas protected from livestock serve as useful adjuncts in evaluating effects of grazing and in following the steps in recovery from overgrazing. Expense of fencing and loss of production usually militate against the use of large exclosures for these purposes. Small areas of an acre or two are valuable for comparison with their immediate surroundings; they do not, however, afford a variety of conditions, such as soil, slope, and aspect, and they are often severely overgrazed by rodents. Thus when the opportunity of studying a large protected area is presented, the study is well worth the time devoted to it. The information presented in this paper was gathered in a 320-acre tract of desert grassland situated about 10 miles south of Silver City, New Mexico. Except for the presence of about forty cattle for a month or two during the spring of 1948, the area has been protected from domestic livestock since 1918. Elevation of the tract is approximately 5,600 feet. The nearest weather station is at Silver City at an elevation of 5,936 feet. Average precipitation at the station from 1878 through 1948, with some breaks before 1911, was 17.05 inches (Long, '47, '49); that from 1918 through 1948 was 16.58 inches. Of the latter average, approximately 69 per cent fell between April 1 and October 31, and 40 per cent between July 1 and September 30. Average precipitation at Deming, about 40 miles south of the study area and at an elevation of 4,331 feet, is 9.71 inches. From 15 years of interrupted temperature records from 1911 to 1946, Long ('47) gives the average date of the last killing frost in spring at Silver City as April 25, and that of the earliest in the fall as October 24. From the same source, annual mean temperature is 53.10 F; annual mean maximum, 66.40 F; annual mean minimum, 39.80 F. July has been the warmest month, with a mean of 72.10 F; January, the coldest, with one of 35.00 F. Owing to its being 300 feet lower in elevation and 10 miles farther from the mountains, the tract under study probably experiences higher temperatures and more wind and between 14 and 15 inches of precipitation.