234 



Light 



flowers are intolerant of shade. The ponderosa pine, for example, 

 requires a light intensity equal to at least 25 per cent of full sunlight. 



Intolerant species cannot develop in the shade of a dense stand 

 of their own or other species. Ecological consequences of this fact 

 for the plant community will be discussed further in later chapters. 

 Even among somewhat tolerant species the first plants to become es- 

 tablished in an open area will grow to better advantage than indi- 

 viduals subsequently developing around them because of the com- 

 petition for light and other needs. Differential growth often results 

 in "pyramiding" in the development of such a group of plants (Fig. 

 6.26). As we have seen in an earlier section, the light on the floor 



Fig. 6.26. Pyramiding due to competition exhibited by a group of spruce trees 

 growing in a Michigan bog. 



of the temperate deciduous forest becomes seriously reduced when 

 the trees leaf out. Many of the smaller plants are adapted to a period 

 of rapid growth in the early spring while light on the forest floor is 

 sufficiently intense. In the marginal rainforest of Panama a dense 

 undergrowth is possible because during the dry season the leaves fall 

 from the trees and allow light to penetrate. In the equatorial rain- 

 forest of Columbia, on the other hand, trees shed their leaves in- 



