318 GEORGE E. NICHOLS 



an area which it is desired to treat as a unit. Let ^4 = the 

 habitat factor "ground permanently covered by water;" and, 

 for the sake of simplicity, let B = the habitat factor ''depth 

 of water." Then, according as B varies, P = A(B)i + A{B)2 

 + A{B)3, etc. In other words, all the habitats of the area P 

 are alike with reference to the habitat factor A, and the series of 

 habitats thus embraced may therefore be regarded as constitut- 

 ing a habitat-complex with reference to this factor. As another 

 illustration, let it be assumed that B = an area which has been 

 burned over; let F = the factor ''fire;" and let H = the factor 

 "humus destruction." Then, according as H varies, B = F(H)i 

 -\- F Hi + F(H)3, etc. The area B may thus be regarded as a 

 habitat-complex with reference to the habitat factor F. 



Intimately associated with the habitat-complex is the associa- 

 tion-complex. The relation between the two is analogous to 

 that between the habitat-type and the association-type. In 

 a pond, for example, correlated with the various individual 

 habitats which comprise the habitat-complex, is a correspond- 

 ing series of associations: the association of submersed aquatics, 

 the Nymphaea association, the Scirpus-Typha association, etc. 

 Similarly, in a salt marsh, there may be as many different as- 

 sociations as there are habitats. And just as the habitats in 

 such unit areas, taken collectively, may be referred to as a 

 habitat-complex, so the group of associations which occupies the 

 habitat-complex may be designated as an association-complex. 

 An association-complex may therefore be defined as: a group 

 or series of associations which occupies, and forms a unit with 

 respect to, a habitat-complex. The various ways in which the 

 term association-complex can be applied need hardly be sug- 

 gested. The associations of any area, taken collectively, may 

 be so designated. The concept finds its most significant ap- 

 plication, however, in relation to the edaphic formation which 

 will be discussed in the following section. 



The association-complex may be referred to in terms of the 

 habitat-complex concerned; thus: pond association-complex 

 (or simply pond complex), salt marsh association-complex, flood 

 plain association-complex, burn association-complex, etc. 



