PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



95 



harvest that removes a high proportion of shoot 

 apices in early stages of culm elongation seriously 

 reduces herbage production. Consequently, culmed 

 vegetative shoots are better adapted to a periodic 

 harvest, scheduled to coincide with advanced 

 stages of growth when the axillary buds are 

 better prepared to initiate new tillers. Under ap- 

 propriate harvest regimes, grasses with culmed 

 vegetative shoots tend to be more productive, 

 but perhaps somewhat less nutritious, than those 

 with culmless vegetative shoots. Additional con- 

 sideration, however, must be given to the pro- 

 portion of shoots becoming reproductive. 



Reproductive shoots. — -Reproductive shoots, 

 also, begin growth in the form of culmless vege- 

 tative shoots. Depending on the fulfillment of 

 minimal vegetative development and essential en- 

 vironmental conditions, some shoot apices differ- 

 entiate to reproductive status. The percentage of 

 shoots becoming reproductive is relevant to grass 

 management because (a) both herbage and seed 

 production tend to increase with the percentage, 



(b) forage quality and resistance to grazing tend 

 to decrease with increase in the percentage, and 



(c) the growth form of reproductive shoots is 

 better adapted to periodic harvest, after rela- 

 tively long periods of growth, than to frequent 

 harvest or continuous grazing. The reproductive- 

 shoot percentage varies greatly among species, 

 and from year to year and place to place within 

 a species {5, 24). For many species, a thin stand 

 has a higher percentage of reproductive shoots 

 than a thick stand; and nitrogen fertilization 

 generally increases that percentage {22). 



With only a little culm elongation, many, if 

 not all, leaves can be removed by cutting just 

 above the rudimentary inflorescence. Subsequent- 

 ly, the culms remain obliged to grow, even 

 though they may remain entirely leafless (7, 10, 

 23, 31). A harvest that cuts below the inflores- 

 cence and peduncle (the uppermost internode of 

 the reproductive culm) stops further growth of 

 that shoot and induces tillering at the base. This 

 is the principle involved in the development of 

 multiple-crop rotation schemes for grazing {20, 

 23). 



Aborted reproductive shoots, those in which 

 the peduncles and rudimentary inflorescences 

 have been killed, soon reach maximum develop- 

 ment. Although they are "blind" shoots, they lack 



the shoot apex and indeterminate growth of the 

 vegetative shoots. Aborted reproductive shoots 

 often lose apical dominance over basal axillary 

 buds and contribute new tillers at an earlier time 

 than exhibited b} T ordinary reproductive shoots. 



Grazing Management 



Information about plant morphogenesis is 

 needed to explain plant responses to range man- 

 agement. Such information can be used to define 

 appropriate seasons or sequences of grazing, 

 where an intensive degree of control over land 

 and livestock can be attained. This assumption of 

 intensive control omits the situation of poorly 

 distributed grazing, for which rotation of de- 

 ferred grazing and rest-rotation grazing can be 

 used to prevent the destruction (sacrifice) of 

 critical sites such as drainage systems. These 

 conventional systems of grazing are discussed in 

 other papers of this workshop. 



Grazing is not only a means of harvesting but 

 a treatment that affects subsequent herbage quan- 

 tity and quality. At a given time and place, graz- 

 ing might be conducted primarily to produce a 

 strong tillering response, harvest a maximum 

 quantity of nutrients per unit area, improve for- 

 age quality for subsequent grazing, manipulate 

 botanical composition, protect and improve ad- 

 jacent range, or create some other desirable effect. 

 All good things cannot be produced on range- 

 land at one time or in one Avay. Thus, the point 

 of emphasis in this section will be that informa- 

 tion about plant morphogenesis can help define 

 opportunities and alternatives for application in 

 grazing management. The examples given are 

 fundamental and illustrative. Their applicability 

 depends on local opportunity, the degree of con- 

 trol over land and livestock, and perhaps other 

 factors. 



Let's consider first a very specific kind of 

 treatment by grazing. Grasses such as squirrel- 

 tail {Sitanion hystrix (Nutt.) J. G. Smith) and 

 needle-and-thread {Stipa comata Trin. and 

 Rupr.) have awns that cause mechanical injury 

 to animals and confound the problem of grazing 

 distribution. The inflorescences can be grazed 

 safely while they are in the boot stage of devel- 

 opment. Thereafter, leafy regrowth by vegetative 

 shoots can be very desirable. The treatment can 

 solve a problem, improve forage quality for a 



