Paper No. 11 



MORPHOGENESIS AND MANAGEMENT OF ANNUAL RANGE PLANTS IN 



THE UNITED STATES 



By Cyrus M. McKell 1 



The annual range plant community is a dy- 

 namic aggregation of plant species which fluctu- 

 ates yearly and seasonally in response to changing 

 weather conditions. Application of various man- 

 agement practices such as grazing management, 

 fertilization, burning, seeding, and chemical 

 sprays can enhance productivity, improve species 

 composition, and change quality tremendously in 

 annual rangelands. The annual range is surpris- 

 ingly more responsive than any other rangeland 

 type. 



The stage of plant development is equally as 

 important as the management practices employed. 

 By careful attention to stages of morphogenesis, 

 including germination, vegetative growth, stem 

 elongation, flowering, and seed production, the 

 application of management practices can en- 

 hance the value of annual rangelands in the 

 United States. 



Location Of Annual Rangelands 



Annual range plant -communities predominate 

 in two major types of climates in the United 

 States. In California, the Mediterranean-type cli- 

 mate consists of moist cool winters and dry hot 

 summers {28). The most favorable periods for 

 plant growth, therefore, occur in the fall, after 

 the onset of precipitation but before low tempera- 

 tures limit plant growth and near the end of the 

 moist season in spring, as temperatures rise after 

 the cool winter period. Plant species that can 

 complete their growth cycle, produce seed, and 

 then escape the long summer drought, appear to 

 be well adapted to the Mediterranean-type cli- 

 mate. Considerably fewer perennial plant species 

 can withstand extreme drought for up to 5 or 6 

 months. With range deterioration, the peren- 



1 Director, Environment and Man Program, Utah State 

 University, Logan Utah 84321. 



nial species give way to the invasion of intro- 

 duced grasses and forbs from the Mediterranean 

 region. 



Annual plant species also are important in the 

 middle-latitude desert, classified as BSK by Kop- 

 pen {28). The northern Great Basin and Colum- 

 bia Basin plains have cold winters with precipi- 

 tation often occurring as snow. Spring growing 

 conditions become favorable as temperatures in- 

 crease and precipitation remains adequate for a 

 short period. Precipitation continues at a low 

 level through much of the summer but is often 

 undependable, and long periods of drought pre- 

 vail. Deterioration of the original vegetative cover 

 of this region allowed the invasion of annual 

 species which were able to germinate, grow, and 

 mature in a short period of time or to endure the 

 periods of summer drought. 



The southern extension of middle-latitude des- 

 erts in the United States, covering large expanses 

 of the Southwest, also have an important com- 

 ponent of the vegetation comprised of annual 

 species. However, in these desert areas the an- 

 nual vegetation occurs as a minor understory to 

 the dominant shrubby vegetation and, therefore, 

 is not considered of high importance from a man- 

 agement or forage production standpoint. How- 

 ever, in an occasionally favorable year, the pro- 

 fuse growth of desert annual species is an inter- 

 esting phenomenon and cannot be dismissed 

 lightly {55). Such desert annual communities 

 serve an important function in the ecosystem by 

 recycling nutrients, by furnishing food and habi- 

 tat to small animals, and by forming a protective 

 plant and litter cover over the soil surface under 

 shrubs. 



The annual range plant community in Califor- 

 nia is a very dynamic aggregation of plant spe- 

 cies that fluctuates, not only yearly but seasonal- 

 ly, in response to the factors and interrelation- 

 Ill 



