[Chap. V 



LOCAL PLANT COMMUNITIES 



43 



A't-Yr. 



S'^-Yr. 



WHITE C. 



mi^ ■<y^'.'-:- 



ORCHARD GRASS 



REDTOP G. 



T.a 



FES. 



WHITE CLOVER 



BLtje: GRASS 



Cf^CHARO G. 



RX 



eti-Yr. WHITE CLOVER 



-.SLyE, GRA.SS: 



CS^CHARD C. 



W 



Fig. 24. Diagram of changes that occurred in a mixed population of plants in a 

 pasture during a period of five years follo\\'ing the first year, when the seeds were 

 sown with those of a nurse crop, such as oats or rye. The comparative yield of each 

 kind of plant from year to year is given. Bluegrass is the only species that continued 

 to increase in amount every season. Data froin R. G. Wiggans. 



peratures are high m summer. Evidently bluegrass can become the sole 

 dominant only in those areas in which each of these several environ- 

 mental factors does not exceed a certain intensity. Where one of these 

 factors is exceedingly high or low, a bluegrass lawn may be obtained 

 only if one is willing and able to adjust the environmental factors to an 

 intensity that is more favorable to the growth of bluegrass. Kentucky 

 bluegrass is most likely to become dominant in lawns with moderate 

 moisture and temperature, abundant light, and loamy soils that are 

 slightly acid but rich in salts of nitrogen, phosphorus, and potassium. 

 With persistent effort one can adjust the relative amounts of most of 

 these environmental factors. 



Preference may be given, however, to another kind of grass that will 

 grow better than Kentucky bluegrass under the local conditions. There 

 are several varieties of bent and fescue grasses that grow well in soils of 

 greater acidity. Consequently in the acid soils along the Pacific Coast 

 and in the New England States bent grass lawns are more common than 

 they are in the Central States. Where the light is insufficient for the 

 growth of Kentucky bluegrass, certain varieties of bent and fescue 



