PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



193 



an earlier report, concerning mixed prairie near 

 Hays, Kans., Tomanek and Albertson (52) found 

 that ungrazed areas were dominated by tall 

 grasses while moderate grazing resulted in re- 

 placement of the tall grasses by midgrasses and 

 short grasses. Heavy grazing nearly eliminated 

 the tall grasses and reduced the midgrasses, while 

 the short grasses increased proportionately. Total 

 basal cover increased with increasing grazing 

 pressure on all sites except the rocky breaks. This 

 increase in basal cover commonly accompanies in- 

 crease in blue grama under heavy grazing in the 

 mixed prairie as described as Sarvis (47). He 

 found that grazing effects resembled those of 

 drought. A number of species that were adversely 

 affected by drought were also injured by heavy 

 grazing. Needle-and-thread (Stipa comata Trin. 

 & Rupr.) and prairie junegrass (Koeleria cristata 

 [L.] Pers.) were listed as examples. A change in 

 species composition of this nature will certainly 

 affect other elements of the microenvironment. 



Halogeton (Halogeton glomeratus [M. Bieb.] 

 C. A. Mey.) invasion of heavily grazed western 

 ranges was discussed by Frischknecht (20, 21). It 

 infested small areas in which the soils were high 

 in both total soluble salts and exchangeable sod- 

 ium in heavily grazed ranges. Then it invaded all 

 heavily grazed units and heavily grazed spots in 

 lightly grazed and moderately grazed units, par- 

 ticularly when they were spring grazed. 



A species of considerably different stature, but 

 also a problem in some areas, is small clubmoss 

 (Selaginella dema Rybd.). Van Dyne and Vogel 

 (53) found that high level of fertility, shading, 

 and mulch accumulation reduced ground cover 

 by small clubmoss in central Montana foothill 

 grasslands. Decrease in cover was greater in areas 

 grazed intensively than in areas protected for 4 

 years. Clubmoss stands on moderately grazed sites 

 or in adjacent protected areas did not change 

 during this period. In this case, the mechanical 

 effects of grazing and trampling by sheep were 

 more detrimental to small clubmoss than to other 

 species present. 



One of the undesirable effects of poor grazing 

 management is conversion to a sagebrush domi- 

 nated type. Data are lacking for change in micro- 

 environmental factors during the conversion, 

 however, in recent years efforts to convert back 

 to more productive range are documented with 



microenvironmental data. In general, removal 

 of sagebrush improves soil moisture conditions, 

 but each situation is unique. Runoff from a shrub- 

 type vegetation will be increased if a layer of ice 

 or frozen soil occurs on the surface during snow- 

 melt. However, a layer of snow caught in the 

 vegetation will prevent freezing at the surface 

 which will improve infiltration and reduce run- 

 off. Alley (2) reported this to be the case in a 

 study on the Red Desert of Wyoming. Areas 

 sprayed to control sagebrush were soon covered 

 with perennial grasses. The grass cover improved 

 infiltration by holding a uniform snow cover 

 which kept the soil surface from freezing. Thus, 

 less water ran off the sprayed areas than from 

 the sagebrush areas. Fisser (19) followed soil 

 moisture and temperature changes in sagebrush 

 and sagebrush controlled areas, with and without 

 grazing in Wyoming. Soil moisture accumulation 

 during the spring was greater on a mesic foothill 

 grassland than it was on an arid desert-shrub 

 type, and the greatest accumulation was in the 

 2- to 5-foot depth in the shrub controlled area 

 of the mesic site. Grazing did not influence mois- 

 ture accumulation on the arid site, but did reduce 

 spring recharge rate in the mesic site. Severe cli- 

 matic conditions restricted revegetation, thus soil 

 moisture released by brush control was not util- 

 ized. Soil temperature was warmest on an annual 

 basis under the shrub-dominated areas, although 

 the difference was only about 1° C. 



Rowe and Reiman (4-6) evaluated the effects 

 of conversion from brush to grass or from brush 

 to grass-forb vegetation on evaporation, ET and 

 surface runoff in the San Gabriel Mountains of 

 California. They found that soil depth, mulch 

 cover, vegetative growth and season had a large 

 influence on the response to conversion from one 

 vegetation type to another. Although grazing was 

 not part of their study, it is reasonable to believe 

 that changes in water regime due to change in 

 vegetation type brought about by grazing man- 

 agement would be influenced by the same factors. 



Conclusion 



Comprehensive information concerning the ef- 

 fects of grazing on microenvironment of range- 

 lands in the United States is scarce. This review 

 brings together information on the effects of 



