

Figure 1-5. The ecological amplitude of cypress {Taxodium 

 distichum) enables it to grow in shallow water. May, North 

 Carolina. (U. S. Forest Service.) 



of wax myrtle {Myrica cerifera) and yaupon {Ilex vomitoria), which 

 is finally succeeded inland by a zone of maritime live oak (Quer- 

 cus virginiana) on the stable dunes. All the zones are exposed to 

 salt spray, the sea oats receiving the most.^' 



Phenological differences, such as the appearance of flowers in 

 species at different seasons of the year, are usually caused by 

 variations in ecological amplitude. Annual species in California 

 deserts have definite and rather narrow limits of amplitude for 

 the amount and duration of precipitation and for temperature 

 conditions while the soil is wet, some species germinating and 

 growing only in the summer, others only in the winter. ^^o 



Plants growing within the optimum range of ecological ampli- 

 tude of the species (Figure 1-5) can be expected to be best in vigor 

 and in greatest density, but even under such conditions competi- 

 tion may have detrimental effects. Usually a species possesses 

 maximum competitive power in a habitat that is in the optimum 

 range. However, as the limits of the amplitude range are ap- 

 proached, the plants become increasingly susceptible to loss of 

 vigor and death, partly because of competition with other species. 



20 



Species axacl Popimlations 



