PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



145 



years. Precipitation was near average or above 

 average during the study. 



Semidesert Grassland 



A number of studies on the Jornada Experi- 

 mental Range, 40 km. north of Las Cruces, N. 

 Mex., have contributed to developing a grazing 

 system (13). The major forage species on the 

 light- to medium-textured soils are Bouteloua eri- 

 opoda (Torr.) Torr. and Sporobolus fexuosus 

 (Thurb.) Rydb. Hilaria mutica and Scleropogo-n. 

 brevifolius Phil, grow on the heavier soils. 

 Under certain weather conditions, there may be 

 an abundance of a variety of forbs and annual 

 grasses. The average annual precipitation is 22.5 

 cm. The average precipitation during the summer 

 growing season is 12.5 cm. The average annual 

 evaporation from a Weather Bureau pan is 225 

 cm. or ten times the precipitation. However, Her- 

 bel and Nelson (13) showed that precipitation 

 averages had little meaning. During 53 years of 

 record, 45 percent of the years had seasonal pre- 

 cipitation of less than 85 percent of average, and 

 34 percent of the years had seasonal precipitation 

 greater than 115 percent of average. Further- 

 more, summer rainfall occurs as localized, convec- 

 tional thunderstorms. 



Forty years ago, there were two major vege- 

 tation types on the Jornada; one dominated by 

 Bouteloua eriopoda, and the other dominated by 

 Hilaria mutica and Scleropogon brevifolius. Be- 

 cause Hilaria and Scleropogon are more palatable 

 and can withstand moderate grazing during the 

 summer growing season, the grazing system con- 

 sisted of grazing the Hilaria-Scleropogon type in 

 summer and early fall, and then grazing the 

 Bouteloua type from late fall until the next sum- 

 mer (28). However, considerable Bouteloua was 

 lost during the severe drought of 1951-56 and 

 due to a rapid increase of Prosopis julifora on 

 sandy soils (3). Now there are other vegetation 

 types made up of a multiplicity of forbs and a 

 few grasses. They can provide a considerable 

 part of the forage crop in some years. Their pro- 

 duction is not as reliable as the long-lived per- 

 ennial grasses,- but they have a high nutritive 

 value (21). Herbel and Nelson (12) found that 

 cattle grazed, to some extent, all species avail- 

 able to them, including a variety of forbs and 

 shrub-like species. They also found that there 



were definite seasonal preferences for some 

 species. 



Using weather and plant information, and con- 

 sidering livestock needs, Herbel and Nelson (13) 

 developed the Best Pasture Grazing System. The 

 system consists of establishing an objective for 

 each range unit and stocking accordingly. The 

 system is opportunistic in that the use of forbes 

 and short-lived grasses is maximized. They are 

 of little value to the permanent range resource 

 but contribute much to livestock nutrition. No set 

 stocking plan is established for a specific time 

 period because of considerable variations in 

 weather conditions that affect plant growth. The 

 system involves a rotation scheme where the live- 

 stock are moved when the vegetation on a de- 

 ferred unit can be grazed to the advantage of 

 both plants and animals as compared with the 

 unit being grazed. In the large range units oc- 

 curring in parts of the West, periodic opening 

 and closing of watering places can be used to 

 rotate grazing pressure to different areas within 

 a range unit (22). 



Conclusions 



Studies on California Annual Rangelands have 

 indicated that yearlong-continuous grazing is su- 

 perior to seasonal grazing. However, species com- 

 position can be manipulated by "grazing intensity, 

 burning, and seeding. This may indicate that a 

 highly flexible grazing system, involving some 

 form of manipulation on part of a ranch opera- 

 tion, may provide a higher quality, quantity, or 

 both of forage for part of the year. 



There was only limited success with any graz- 

 ing scheme other than continuous on rangelands 

 grazed only for a part of the year. There has 

 only been a modest increase of the grazing period 

 at Harvey Valley following 13 years of rest-ro- 

 tation grazing, and this may be due to range 

 improvements such as seeding, brush control, 

 fencing, and water development. At the Starkey 

 Experimental Forest, the production of Carex 

 geyeri, was maintained only with light stocking 

 in a deferred-rotation system. However, there 

 was a spring drought during the study and 

 Carex is very susceptible to grazing. At Mandan, 

 the vegetation in the rotation units did not show 

 the adverse effects of grazing during a period of 

 below-average precipitation as did the unit grazed 



