NATURE OF THE COMMUNITY 



29 



culiar to the area. The same growth form is repeated in a few 

 widely separated regions of the world where, although made up 

 of quite different species, it is a product of a similar complex of cli- 

 matic conditions. In the same way the vast expanses of deciduous 

 or coniferous forests in the temperate regions of the world are 

 each found where climatic characteristics fall within definite 

 limits, similar throughout. 



General Climate and Vegetation Type.— Within the general 





FlG. 9. Transition zones between stands of two life forms. The forest at 

 right (mostly buckeye) shows the usual gradual transition from a closed 

 stand to scattered, widely spaced individuals over a wide band— such as is 

 typical of most transitions from one community to another. The abrupt 

 transition from beech forest to grassland (at left) is unusual— Photo by D. 

 M. Brown. 



vegetation type, certain variations may be expected. Species dif- 

 ferences are not uncommon although the growth form may be 

 uniform for all. Such differences are most pronounced when a 

 type of growth form extends over a wide latitudinal range. In the 

 arctic flora, which has an otherwise uniform physiognomy, the 

 number of species declines steadily northward. Within the grass- 

 land areas of the Middle West, there is obvious uniformity of 

 growth form from Canada to Texas, yet some species found in the 

 south are not found in the north and other species may be found 

 only in the north. Even those species that seem to range from one 



