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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



stages. Onl} - through the formation of lateral 

 flower stems is this vulnerability rendered less 

 critical. The high density of plants growing on 

 annual range virtually assures adequate seed 

 production in most years, if intense grazing does 

 not destroy the developing inflorescences. How- 

 ever, the number of plants which survive to the 

 flowering stage is drastically reduced from the 

 number of plants which germinated at the be- 

 ginning of the season. 



In earlier growth stages, fertilization was val- 

 uable in encouraging plant growth, but at flow- 

 ering there is little benefit from fertilization. In 

 fact, it may be detrimental if it has hastened 

 maturity by depleting the soil moisture supply. 



Palatability often changes as flowering ap- 

 proaches. T. asperum becomes much less palat- 

 able at the boot stage (33). Many forbs, par- 

 ticularly the annual legumes, take on a degree 

 of unpalatability at this stage. Silica and fiber 

 contents increase, and many plants become much 

 rougher and stiffer in character. 



Seed Maturity 



As seeds begin to develop, carbohydrates are 

 translocated to the seed heads of grasses and 

 forbs. Concurrently, maturation of other plant 

 parts proceeds rapidly. Photosynthesis is ex- 

 ceeded by respiration in older plant parts, and 

 lower leaves begin to die. In the annual range, 

 soil moisture stress is a common and prevalent 

 environmental condition and becomes an over- 

 riding effect in hastening plant maturity and 

 seed ripening. Management of annual range- 

 lands at this stage may concentrate on several 

 practices designed to manipulate the plant cover 

 or to make continued use of the forage resource. 



Range fertilization increases plant palatabil- 

 ity, which provides excellent opportunities for 

 continued grazing of the dry herbage. Less pal- 

 atable species, when fertilized, have been ob- 

 served to be consumed readily by livestock (43). 

 The forage produced by fertilization is high in 

 protein and other nutrients for the grazing ani- 

 mal (52). 



Seed maturity of undesirable species can be 

 prevented with herbicides during the period of 

 seed maturation (9). Aminotriazol has effective- 

 ly prevented the development of seeds of T. as- 

 perum, a late-maturing species. Late-maturing, 



weedy species have been controlled by fire, which 

 destroys their immature seeds after the desirable 

 forage species have matured (14)- During a 

 critical period of 1 or 2 weeks, the early-matur- 

 ing, annual forage species are dry enough to fur- 

 nish fuel to support a fire which will destroy the 

 maturing crop of medusahead seeds (41)- Burn- 

 ing after the maturity of medusahead seeds is 

 considerably less effective, because the hard seeds 

 have been cast from the heads and lost into the 

 litter, where they are protected by the volume 

 of plant material and are unaffected by the pass- 

 ing of a fire over the area. In addition, mature 

 seeds are less susceptible to the effects of high 

 temperature (29). 



Seed Dissemination 



Dissemination of seeds from annual range spe- 

 cies occurs at various times following maturity, 

 depending on weather conditions and the struc- 

 ture of particular species. Seeds may be cast in- 

 dividually, as in Bromus tectoi*um. Bromus mol- 

 lis, Taeniatherum aspei*um, Arena barbata, and 

 Tri folium subterraneum ; or by dehiscence of en- 

 tire seed heads of Aegilops triuncialis L. 



Seeds of annual species often have undesir- 

 able characteristics, such as spines, stout barbed 

 awns, or coiled seed stalks, which catch in the 

 fleece of sheep and reduce its value. These struc- 

 tures for attachment may provide an effective 

 means of dissemination and even a means of 

 transport and invasion to new range areas. 



Management practices that may affect seed 

 dissemination include removal of grazing ani- 

 mals (Erodium areas) before seed dissemination, 

 restriction of livestock to weed-free areas, and 

 burning. Some are ineffective : burning may ac- 

 tually scarify seeds, reduce litter cover and im- 

 prove conditions for seedling establishment. Re- 

 moval of livestock may not be realistic unless al- 

 ternate feed sources are available. 



Summary 



Management of annual rangelands has grad- 

 ually developed on a foundation of established 

 biological principles. For example, we utilize in- 

 formation on nutritional requirements and phen- 

 ology of plants as a basis for management deci- 

 sions. 



