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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



are again favorable and plants are in the rosette 

 stage, favorable nutrition will aid rapid develop- 

 ment towards maturity. 



Fire may be used as a management tool during 

 seed development and at the mature plant stage. 

 The mature plant stage is not really a stage of 

 growth but of existence in which the fire re- 

 duces dry litter and concentrates the surviving 

 seed at the soil surface. The desired result is not 

 to stimulate plant growth but to reduce undesir- 

 able species growth. Herbicides may be applied to 

 reduce or eliminate seed formation of undesirable 

 species, to retain plants in a given stage of de- 

 velopment or to restrict other species from com- 

 peting in the early seedling establishment phase. 



In the following sections these management 

 practices are described as they work specifically 

 on developmental stages of annual range species. 



Comparative Phenology 



In dense populations of annual forb and grass 

 seedlings, rapid growth results in a high demand 

 for light, moisture, nutrients and other environ- 

 mental factors (9) . Plant survival under such cir- 

 cumstances will be attained only by seedlings of 

 high vigor, or by those with different rates of 

 morphogenesis which allows them to avoid the 

 stress period by earlier or later development. In 

 reporting the characteristic growth curve for the 

 annual type, Ratliff and Heady (Ifl) reported 

 that the period of most rapid growth extended 

 from March 28 to April 24. In 1960, growth of 

 Erodium botrys and Medicago hispida Gaertn. 

 was earliest, followed by Avena barbata Brot., 

 Bromus rigidus Roth, and Bromus mollis, with 

 Lolium multiforum Lam. being latest. The pro- 

 gression of plants towards maturity reached a 

 static period of maximum herbage weight at the 

 time of seed development. Medicago hispida was 

 an exception, in that the maximum period ex- 

 tended from the onset of flowering to the time of 

 leaf shatter. After the peak of maturity, plants 

 began to lose weight as seeds were cast, but rye- 

 grass lost its weight only half as fast as the 

 other species. 



Species with delayed maturity often present 

 opportunities for applying management practices. 

 Tarweed (Ilemizonia spp.), a summer-maturing, 

 noxious plant, can be controlled simply by range 

 fertilization which stimulates the growth of 



earlier maturing species and thus depletes the 

 supply of soil moisture available for tarweed 

 summer growth {65). Lotus purshianus (Benth.) 

 Clements & Clements and Taeniatherum asperum 

 (Sim.) Nevski also have late growth habit and 

 depend on the soil moisture remaining after other 

 range species have matured (39,1$). 



Bromus tectorum L. is normally a winter an- 

 nual, germinating in the fall when rain is suffi- 

 cient and growing rapidly until cold tempera- 

 tures set in, but it may act as a spring annual if 

 there is too little fall moisture available for ger- 

 mination. Hulbert (16) noted striking variation 

 in the phenology of plants grown at Lewiston, 

 Idaho, from seeds obtained from several geo- 

 graphic locations. There was a range of about 25 

 days in the time of emergence of the inflorescences, 

 and about 20 days in the time when plants turn 

 completely brown. These ranges in dates of ma- 

 turity are in striking contrast with the phenol- 

 ogical development of the perennial grasses with 

 which cheatgrass is a competitor in the northern 

 Great Basin. 



The implications of differences in phenological 

 development for grazing management systems are 

 not exactly clear. Much more knowledge is 

 needed about the physiological status of plants in 

 relation to morphogenesis before improved tech- 

 niques, such as hormone sprays and herbicides, 

 can be used to condition plant development. 



Germination 



The seemingly simple process of seed germina- 

 tion initiates a long series of morphogenetic 

 changes that ultimately lead to a mature plant 

 and reproduction of the species once again. The 

 annual habit allows a rapid turnover of the gene 

 pool and the annual exposure of all possible 

 genetic combinations to environmental stresses, 

 thus eliminating the unfit individuals from the 

 population. Perhaps this is why annual species 

 are so highly adaptable and vigorous ; it is simply 

 a matter of selection for such habitats. 



Favorable temperature and moisture are es- 

 sential for successful development of the seedling 

 during the first critical stages of growth. Numer- 

 ous management practices can be used to stimu- 

 late, retard, or eliminate plant growth during 

 germination and seedling establishment. 



A high degree of priority exists for seedlings 



