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Basal area data, collected from five sites in 1963 and 1976, were compared to determine the effects of 13 years of above-average rainfall in the growing season (April through September) on native range vegetation of the northern Great Plains. Changes in basal area, composition, and forage production were analyzed for five major grass and grass-like species. During the 13-year aboveaverage rainfall period, western wheatgrass (Agropyron smithii), needleandthread (Stipa comata), and prairie junegrass (Koeleria cristutu) established or increased on all sites. Threadleaf sedge (Carex filifoliu) increased on the silty thin hilly range sites but decreased on the sandy range sites. Blue grama (Boutelouagracilis) decreased on all sites. Calculated forage yield of these five species more than doubled on the silty (110%) and thin hilly (109%) range sites and increased 61% on the sandy range sites. The increase in forage yield decreased the amount of land needed for grazing by 1.6, 0.7, and 2.4 ha/cow-month for the silty, sandy, and thin hilly range sites, respectively. It is well known that changes in precipitation will alter the floristic composition of short and midgrass prairies in the northern High Plains (Perry 1976). Many investigators have discussed the effects of droughts upon rangeland vegetation but, as Coupland (1959) and Perry (1976) have stated, little information has been published correlating the effects of many years of near-normal or above-normal precipitation upon this vegetation. The authors are range biologist, Montana Department of Natural Resources and Conservation. High Plains Experiment. P.O. Box 1350, Miles Citv. Mon. 59301: range scientist, U.S. Dep. Agr. Agricultural Research Service, Sidney, Mon. 59270; and program manager, Montana Department 01 Natural Kesources and Conservation, High Plains Experiment, Helena, Mon. 59601;and assistant Professor, Department of Forest Science, Oregon State University, Corvalhs 57331. I ne autnors wlsn to tnank Ann Losmski tar her unttrmgetforts in pfanimetering the basal area maps. We also thank Drs. D.N. Hyder, R.T. Coupland. R.S. White, and A.B. Super for reading and commenting on the manuscript. This study was partially funded through Contract No. 14-06-D-7577 from the Office of Atmospheric Resources Management, Bureau of Reclamation to the Montana Department of Natural Resources and Conservation as part of the High Plains Experiment. Manuscript received November 29, 1978. 246 The short and midgrass prairies are continually changing, with climatic variables determining the degree of dominance of each species. Generally, during extended dry periods, total basal area decreases and species composition shifts toward domination by the short grasses. During the drought of the 1930’s, blue grama (Bouteloua gracilis), western wheatgrass (Agropyron smithii), and needleandthread (Stipa comata) were reduced approximately 90% in eastern Montana (Ellison and Woolfolk 1937; Hurtt 1951; Reed and Peterson 1961). This drought reduced threadleaf sedge (Carex filzfolia) only 12 to 55%. In southern Alberta, Clarke et al. (1947) reported that total basal cover was reduced from 26% in 1929 to 21% in 1936 and then to 14% by 1939. In eastern Montana, needleandthread and prairie junegrass (Koeleria cristata) appear to be the least drought-tolerant species, whereas blue grama and threadleaf sedge seem to be the most drought-tolerant species (White et al. 1978). During extended periods of above-normal precipitation, total ground cover may increase, and range vegetation may shift toward a more mesic type in which the midgrasses play the more dominant role (Coupland 1958). Coupland (1959) reported that precipitation averaged about 20T0 above normal and temperature 1.7 to 2.8 C below average between 1950 and 1954 in Alberta and Saskatchewan, Canada, and that total basal area of grasses on ungrazed to moderately grazed sites in the mixed grass prairie doubled between 1944 and 1954 and the calculated forage yield increased by 137%. The two principal species in this region, porcupine needlegrass (Stipa spartea var. curiseta) and thickspike wheatgrass (Agropyron dashystachyum), increased from 15 to 3 1% in total composition and forage yield increased from 29% to 50%. In contrast, the two principal species of drier situation, needleandthread and blue grama, declined from 62% to 44% in total composition and the calculated forage yield declined from 54 to 38%. JOURNAL OF RANGE MANAGEMENT 33(4), July 1960 Five permanent sites, representing the native range vegetation near Mildred, in southeastern Montana, were mapped by basal area in 1936, 1938, and 1963. These sites provided us an excellent opportunity to document changes in range composition because the growing season precipitation (April-September) in this area between 1963 and 1976 averaged 23% higher than the mean of the previous 13 years (1949-1962). We believed that changes in vegetation occurring under natural conditions might be a good predictor of the possible long term consequences of many years of successful spring-early summer cloud seeding. Evidence to date indicates that cloud seeding may result in precipitation increases of lo-70% (Cleveland et al. 1978). Therefore, the objective of this study is to document changes in basal area between 1963 and 1976 after 13 years of above-average rainfall and relate this to changes in forage yield. tistically to the previous 13 and 35 year averages (one-tailed Student’s t-test). Since we are interested in major effects of above-average precipitation, data obtained in 1963 were compared with the data from 1976, after 13 years of above-average precipitation. Site Descriptions The vegetation was charted using a 30 X 152-cm frame strung with wire forming 5 X 5-cm grids. Basal area of plant species, ant hills, cow chips, and other materials occupying area within the frame were mapped on graph paper at ‘/2 scale and then planimetered at least twice to assure accuracy. The basal area data were used in determining composition changes during the study period of all grasses, shrubs, half shrubs, and forbs. A one-tailed paired comparison t-test was used to statistically compare basal area changes on the range sites. Because western wheatgrass, blue grama, needleandthread, prairie junegrass, and threadleaf sedge are the important grasses or grass-like species for forage production in this region, the data for these species were analyzed further for changes in percent total ground cover between 1963 and 1976. Within each of the five permanent sites, five 30 X 152-cm (1 X 5 ft) permanently marked plots were originally located about 130 m (426 ft) apart. All plots have a north-south orientation and location was restricted to similar type range. Some plots were lost over the years, leaving five plots each at sites 1 through 4 and three plots at site 5 in 1976. The soils at these sites were classified by the Soil Conservation Service (Table 1). Sites 1 and 2 were classed as silty, site 3 as sandy, and sites 4 and 5 as thin hilly range sites. To minimize the effects of different soils, the basal area data on similar range sites were combined. Grazing was heavy on all sites until allotments were formed in the late 1940’s. Since then, the Bureau of Land Management records in Miles City show that the grazing pressure at each site between the two periods ( 19491962 and 19631975) was relatively constant. Sites 1 and 3 have been grazed lightly to moderately by cattle from April to October. Site 2 has been grazed only occasionally although heavily by cattle and sheep. Site 4 has received only moderate grazing by cattle and sheep during the winter and early spring since 1940. Grazing on site 5 has varied from moderate to heavy from April to October. To obtain a relative estimate of forage yield, percent basal area for these five species was converted to Stipa equivalents (Brown 1954; Clarke et al. 1947). Forage yield is first converted in terms of needleandthread cover by multiplying the figure for relative yielding capacity (relative production) of each species by its percentage basal area. A stand of needleandthread (the standard) with 100% cover yields 2,268 kg of air-dry forage per acre in southeastern Alberta (Clarke et al. 1947). This standard was used in calculating forage yield. These values were then used to calculate an estimate of grazing capacity for cattle, assuming that a 453.5 kg (I ,000 lb) grazing beef cow: (1) may graze 55% of the available forage and (2) will use 299 kg (660 lb) of forage per month on a dry-weight basis (Brown 1954). Since the relative yielding capacity figures used were those developed for the Canadian grasslands, the actual yield of various species under the conditions encountered in eastern Montana may be different. However, for a comparative study (1963 production vs. 1976 production) use of the Canadian relative yielding capacity figures is quite justified.

Effects of Increased Rainfall on Native Forage Production in Eastern Montana