NATURE OF THE COMMUNITY 



25 



and a final stratum of fungi, bacteria, and algae in the upper layers 

 of the soil can also be recognized. The species making up these 

 lesser strata probably offer little direct competition to the trees 

 above them. Most of these plants have appeared, and are able to 

 survive, here because of conditions provided by the tree strata. 



FlG. 6. Stratification in an oak-hickory forest community as seen in spring 

 when the subordinate tree stratum is especially marked by flowering of dog- 

 wood and redbud.— Photo by H. L. Blomquist. 



Indirectly, however, they may offer serious competition to the 

 continued dominance of the trees because, if the trees are to main- 

 tain themselves in the community, they must be able to reproduce 

 themselves. If the seedlings of tree species cannot meet the compe- 

 tition of lesser species, whether it be in the herb or shrub stratum, 

 such trees must eventually disappear from the community. Thus 

 permanent or true dominance involves the ability to compete suc- 

 cessfully in all strata of the community. The effects of competition 

 are most apparent in the lesser strata, and undoubtedly competi- 

 tion is greatest between the seedlings of species of all strata since 

 all must start small and in the same restricted environment of the 

 forest floor. 



Some ecologists maintain that each of these strata is itself a com- 

 munity (synusia), which should be considered as a distinct unit of 

 vegetation. Whether or not the strata are so recognized, they can- 

 not be neglected in any study of communities. Often an under- 



