PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



119 



pact upon species composition. Jones and Evans 

 (21) reported that the percentage of Bromus 

 mollis in a resident annual range was increased 

 by nitrogen fertilization for 2 or 3 years, but in- 

 creased only in the first year on ungrazed plots. 

 Walker and William (54) reported a nitrogen 

 buildup in the soil by annual legumes which 

 had been fertilized with sulfur. The nitrogen 

 buildup increased grass production. Most of 

 these species composition changes occurred as a 

 result of interspecific competition, during seed- 

 ling establishment stage and the initial stages 

 of rapid growth at the end of winter. 



Removal of plant tissue at the beginning or 

 soon after the initiation of rapid plant develop- 

 ment, by either clipping or grazing, reduces 

 plant vigor and encourages less palatable and 

 competitive species to predominate. However, if 

 grazing is not excessive in the early stages, an- 

 nual vegetation has a remarkable ability to sus- 

 tain a high intensity of grazing and yet to con- 

 tinue its growth and proceed towards maturity. 

 It is during this period of active growth that 

 the annual range begins its period of highest 

 productivity. 



Stem Elongation 



Under continued favorable environment, the 

 meristematic regions at the base of each inter- 

 node in the compact grass stem take on new ac- 

 tivity. Formation of new cells and cell elonga- 

 tion are responsible for the relatively rapid 

 growth of the culm in the grass plant. 



Competition for space is extremely intensive 

 at this stage. Some plants, by their greater vigor 

 or by a leaf display pattern, may have the edge 

 in competition with other species. Again, graz- 

 ing and fertilization are most important during 

 the stem elongation stage. Grazing may re- 

 move the immature inflorescences, which grow in 

 the protection of the rolled sheath or in the 

 boot. Some workers (30, 49) pointed out that not 

 all species react the same to herbage removal. 

 B. mollis was found to continue tillering and 

 heading much longer than Festuca megalura 

 Nutt., when clipped ir> a like manner. If graz- 

 ing were continued to the growth terminal stage 

 of F. megalura, it would depress this species, yet 

 would still permit tillering and abundant head- 

 ing in B. mollis. 



High levels of fertilization on annual range 

 species stimulate active growth but also acceler- 

 ate the use of soil moisture. In years of inade- 

 quate rainfall, fertilization may cause the utili- 

 zation of available soil moisture before the plants 

 mature a full crop of seeds (38). However, under 

 other conditions, the more efficient utilization of 

 soil moisture will leave none for summer grow- 

 ing weeds (65). Studies in the Sacramento Val- 

 ley on fertilized range indicate a 300 percent in- 

 crease in efficient use of soil moisture where plots 

 were fertilized with 100 lb./acre of nitrogen and 

 88 lb./acre of phosphorus (39). 



Clipping, as opposed to grazing for clearing 

 an area, may alter species composition. Murphy, 

 Jones, and Love (4-4) reported that clipping en- 

 courages the summer growing forbs. Clipping 

 appears to increase the level of soil moisture re- 

 maining for species which develop late in the 

 summer. 



To preserve the high content of protein, phos- 

 phorus, and carbohydrate, Kay and Torell (25) 

 suggest using a chemical preservative, such as 

 paraquat (l,l'-dimethyl-4,4'-bipyridinum dichlo- 

 ride), to stop plant development and "cure" the 

 standing forage for use by grazing animals. 

 With greater emphasis on forage quality in the 

 future, and where there is no need for the re- 

 plenishment of seeds for stand reestablishment, 

 the practice of chemical curing may offer ad- 

 vantages to land managers. 



Boot Stage To Flowering 



At this stage of morphogenesis, the inflores- 

 cence is ready to emerge from the rolled leaf 

 sheath, and to continue development towards an- 

 thesis and seed maturity. In annual grasses this 

 is a vulnerable stage, because plants are still 

 palatable and the immature seed heads may be 

 subjected to grazing. In annual forbs the prob- 

 lem is not so critical, because many of them do 

 not have a determinant type of flowering, but 

 produce flowers on lateral branches, sometimes 

 throughout the spring period. Erodium and 

 Medicago hispida are particularly well adapted 

 in this regard; flowers appear very early and 

 continue until very late. Some of the annual 

 legumes, such as T. incarnatum and T. hirtum, 

 have a determinant flowering pattern, and are 

 more vulnerable to grazing during these late 



