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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



and blade. Broadleaved species, such as Erodium 

 and the annual legumes, also show the effects of 

 crowding in the earl} 7 seedling stage. Knight 

 and Hollowell (27) pointed out that stand 

 density has a marked effect on the number of 

 vegetative stems, and later on the number of 

 seed heads, produced by Trifolium incarnatum 

 L. Erodium plants tend to spread out and form a 

 mat when surface area is available. This morph- 

 ological characteristic may or may not be an 

 advantage in competition with the annual 

 grasses. 



With the onset of cool weather and lower light 

 intensities during the winter months, many of 

 the annual range species will maintain them- 

 selves in a rosette stage, to continue through the 

 less favorable growing conditions. Because of a 

 temporary plateau of the growth curve at this 

 point, it might be appropriate to refer to the 

 typical annual range species as a winter bien- 

 nial. However, because annuals do not continue 

 their growth through the dry summer period 

 they actually do complete their growth in the 

 single season typical of annual plants. 



Low temperatures often stimulate the axillary 

 buds on stems to produce additional new tillers. 

 Davis and Laude (6) found that the main culm 

 produced more shoots and more heads than did 

 later developing tillers. Reduced light intensity 

 at the basal tissues of closely spaced shoots, and 

 shading by screens, reduced tillering in the an- 

 nual grass, Bromus mollis. This would corres- 

 pond to the plant response seen in the field, 

 under less favorable environmental conditions of 

 winter. Competition for light among species of 

 annual clovers was also found to be a critical 

 matter in the morphology of the seedlings. Wil- 

 liams (60) found that leaf area and leaf po- 

 sition in the foliage canopy of Trifolium Mr- 

 turn, T. incamatum, and T. subterrarueum Linn, 

 was related to the size of the cotyledonary leaves. 

 This advantage was later extended to larger uni- 

 foliate leaves and in the higher elevation of 

 unifoliate and first trifoliate leaves. 



Some species seem to influence or interfere 

 with the growth of other species. Lolium multi- 

 forum (37) in a mixture of species always had 

 a detrimental effect on the growth of these spe- 

 cies, particularly during the seedling stage. The 

 implications of these findings are clear for the 



range manager who uses a seeding mixture con- 

 taining the highly competitive L. multiforum. 



McCowan and Williams (35) found that Ero- 

 dium botrys, grown with Bromus mollis, ac- 

 quired a disproportionate share of available sul- 

 fur, because of its more rapid root extension. 

 However, at high sulfur levels Bromus became 

 increasingly competitive and, as its population 

 density was increased, Erodium was virtually 

 eliminated. Many studies (2, 13, 22, 23, 63, 6k) 

 have shown that fertilizer stimulates plant 

 growth, even during periods of cool tempera- 

 tures. Fertilized plants appear to have an in- 

 crease in cold tolerance. The amount of litter 

 left remaining on the ground from the previous 

 season may be useful as an insulating layer (11). 



Species of annual legumes appear to have dif- 

 fering abilities to take up phosphorus from the 

 soil. Apparently, introduced legumes have a 

 higher potential for phosphorus uptake than 

 some of the native species (1$). Additionally, 

 there appears to be an advantage in phosphorus 

 uptake to offset the effects of low temperature. 

 Other workers (8, 1(3, 54) have shown that ap- 

 plication of fertilizers during the seedling stage 

 will accelerate growth and provide for earlier 

 range readiness than plants which have not been 

 fertilized. 



Rapid Vegetative Development 



Upon emerging from the cool winter periods, 

 plant morphogenesis begins dramatic changes. 

 The significant morphogenetic changes are leaf 

 sheath and blade elongation in grasses and stem 

 and leaf growth in forbs. Eoot and top growth 

 of plants begin a rapid rate of increase, and 

 competition for nutrients, light, water, and space 

 again becomes extremely critical. Only those 

 species which have been able to develop an ade- 

 quate leaf area and root sj-stem will be capable 

 of survival and development in this more ac- 

 tive period of growth (3). 



Under some conditions, an earlier rate of read- 

 iness can be obtained through fertilization (34). 

 Fertilization, through its effect on differential 

 species response, also has a significant impact on 

 species composition. Evans (18) reported dif- 

 ferences in nitrogen uptake among three species 

 of the annual grassland type. Combinations of 

 grazing with fertilization have a significant im- 



