





Figure 1-11. Competition is intense between individuals of 

 one species, the red pine {Pinus resinosa), in this 25-year- 

 old stand. Minnesota. (U. S. Forest Service.) 



existence results in a pattern in which the spacing of the survivors 

 is adapted in high measure to the resources of the environment, 

 e.g., bunchgrasses which are more closely spaced in mesic than 

 in xeric sites. When two species of the same genus, occurring in 

 the same region, are very similar in growth-form and phenology, 

 such as Andropogon scoparius and A. virginicus in the southeastern 

 United States, they do not usually occur together in the same 

 stand in similar spacing or abundance. One is usually numerous, 

 the other sparse, indicating that there must be differences in re- 

 quirements or ecological amplitude not evident in the gross life- 

 form or phenology, which give one the advantage in competition 

 over the other in certain habitats. These differences may explain 

 in part why associated plants usually belong to different genera, 

 for then they are more likely to be sufficiently dissimilar in re- 

 quirements and amplitudes so they can associate without com- 

 peting. One species may grow well in the shade of another 

 because of differences in light requirements, another species may 

 absorb water and nutrients at a different level or at a different 



28 



Species aztd Popimlations 



