PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



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cipitation, the annual plants germinate in the 

 fall, grow slowly until early spring, grow rapid- 

 ly for about 6 weeks, and are usually mature and 

 dry by June 1 (10). The size of the forage crop 

 is related to weather conditions and may differ 

 over 100 percent between years. The species com- 

 position also varies widely from year to year. The 

 various species mature at different times during 

 the spring. In planning a grazing strategy, sev- 

 eral points are important; the short and variable 

 time when species mature, variable maturation 

 dates of desirable and undesirable plants, a wide 

 difference in forage quality as related to available 

 moisture and stage of maturity, and fluctuations 

 in stage of maturity due to site (10) . 



Light utilization by livestock results in an in- 

 crease of the tall annual grasses and a decrease 

 of the desirable forbs. Heavy grazing use in the 

 fall reduces plant growth in the winter (2). 

 Heady (9) showed that mulch in excess of about 

 784 kg./ha. favored the tallest grasses. With no 

 mulch, the vegetation was composed of undesir- 

 able forbs and grasses, and the herbage yields 

 were reduced to about half of the mulch plots. 

 From these studies, Heady (10) concluded that 

 degree of utilization is important in determining 

 the characteristics of the next crop. 



Hervey (14-) changed the species composition 

 with burning treatments and Heady (10) with 

 seeding and mulch manipulation. There seems 

 little doubt that composition of the annual type 

 can be changed, but the results are temporary 

 and last only as long as the treatment is main- 

 tained. 



Studies at the San Joaquin Experimental 

 Range in central California (average annual 

 precipitation of 46 cm.) showed a consistent ad- 

 vantage of yearlong-continuous grazing over sea- 

 sonal grazing in breeding cow performance and 

 calf weaning weights. The best balance of season- 

 ally preferred plant species occurred on ranges 

 grazed continuously yearlong (5). Similar re- 

 sults were obtained with sheep at Hopland. One 

 range unit was divided into three divisions. One 

 division was grazed in the early part of the grow- 

 ing season, one in the middle, and the third near 

 the end of the growing season. The stocking pe- 

 riod was rotated oh an annual basis so that each 

 division was grazed at each time only once in 

 3 years. The sheep were allowed to graze all three 



divisions during the dry season. The average 

 weaning weight of lambs has been consistently 

 higher in the range unit with yearlong-continu- 

 ous grazing. The grazing treatments did not affect 

 species composition, density, or herbage produc- 

 tion. 



The Pacific Bunchgrass Region 



A study conducted at the Burgess Spring Ex- 

 perimental Range in northeastern California dur- 

 ing 1936-51 (16) led to the design of a rest-rota- 

 tion grazing system. Numerous lava flows and a 

 few high peaks top an extensive plateau with an 

 elevation that ranges from 1,068 to 2,440 m. In- 

 terspersed among the mountains are many plains 

 and valleys. Some of the valleys are closed or 

 poorly drained. Annual precipitation during 

 1935-54 averaged 46 cm. at Blacks Mountain 

 Experimental Forest, 19 km. from Burgess 

 Spring. On the average, 74 percent of the total 

 occurred October 1-April 1, primarily as snow; 

 21 percent occurred April 1-July 1 ; and 5 percent 

 during July 1-October 1. The snowpack aver- 

 aged 46 cm. Average daily temperatures ranged 

 from —5° C. in January to 14° C. in July. 



Grassland, sagebrush, juniper, and pine types 

 occupied 63 percent of the total area at Burgess 

 Spring and furnished most of the forage used 

 by livestock. The remaining area, of little use to 

 livestock, was dominated by trees and shrubs. On 

 97 percent of the grazeable range, the primary 

 species were bunchgrasses and other perennial 

 plants that reproduce from seed. The grassland 

 type was made up of wet meadow, closed basin, 

 drained basin, and terrace sites. The major plants 

 were Festuca idahoensis Elmer., Poa nevadensis 

 Vasey ex. Scribn.. P. secunda Presl., Deschamp- 

 sia caespitosa (L.) Beauv., Sitanion hystrix, sev- 

 eral Carex L. sp., and various forbs, shrubs, and 

 trees. 



The average seasonal development of herba- 

 ceous vegetation in the pine type was illustrated 

 with Festuca idahoensis. Growth began about 

 April 1 after the snowpack melted, and ended 

 with seed ripening in early August. Half the 

 seasonal yield of herbage was produced by the 

 end of May and 90 percent by the end of June. 

 Some plant species developed earlier and some 

 later than Festuca; development also varied as 

 much as 33 days from year to year. Herbage 



