use the environmental resources at different times or in different 

 spaces. Association results at times because some species require 

 the shade cast by taller plants or the protection from grazing 

 afforded by cacti or thorny shrubs. Nutritional advantages may 

 occur, as in grasses and legumes growing together; for example, 

 both bromegrass and alfalfa, or Ladino clover, benefit when 

 planted for hay or pasture, as is commonly done in the Corn Belt 

 (see Figures 1-14 and 1-15). Bromegrass produces more stems, 

 more growth after cutting, and more seeds because of the nitrogen 

 supplied by the legume, while the protein content of the alfalfa 

 is greater than when it is grown alone, probably because of de- 

 creased loss of leaves. Birdsfoot trefoil when grown with grasses 

 shows less lodging and increased yields of seed, but tall orchard- 

 grass and timothy tend to delay its maturity. When grown with 

 Kentucky bluegrass, trefoil's ripening was the same as when 

 grown alone. After the first harvest year, mixtures produced 

 slightly higher yields than the trefoil in single culture.*' In a 

 seeded Festuca-Agrostis grassland reverting to original sward, 

 Lolium perenne and Trifolium repens were positively associated, but 

 lack of association existed between Agrostis tenuis and these two 



Figure 1-16. Successful association of longleaf pine {Pinus 

 palustris) and carpetgrass {Axanopus compressus) is shown 

 in two well-defined layers in the summer aspect. August, 

 Tifton, Georgia. (U. S. Forest Service.) 



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