^°1908^^] Adams, Ecological Succession of Birds. 123^ 



The study of ecological plant geography is an extensive one, but 

 many of the details, so important to the botanist, are of much less 

 concern to the ornithologist, Avho needs primarily to know the major 

 plant associations or formations and their successional relations. 

 This implies al>ility to recognize dominance among plant species 

 and the general method of transformation from the dominance of 

 one to that of another. 



By a plant formation is meant that association of species (or plant 

 society) which is correlated with those conditions which tend to 

 prevail over a large geographic area in the last stages of mutual 

 adjustment of all environmental and biotic processes. Such an 

 association or formation tends to occupy such an area to the exclu- 

 sion of all others, and is thus a climax society. 



But absolute dominance of a formation does not occur, because 

 local conditions break the monotony where streams, water basins, 

 bare rock, and similar influences may interrupt the desert, grass- 

 land or forest, and produce minor habitats and associations of both 

 plants and animals. 



It is not my purpose to discuss in detail the various plant forma- 

 tions of (extra-tropical) North America, but to outline those which 

 are of evident ornithological utility. The following may be recog- 

 nized provisionally : — 



1. The Arid Deserts of Southwestern U. S. and the Mexican Plateau. 



2. The Grasslands of the Great Plains. 



3. The Deciduous Hardwood Forest of Southeastern U. S. 



4. The Coniferous Forests of Eastern Canada. 



5. The Giant Conifer Forest of the Pacific Coast and the Rocky Moun- 



tains. 



6. The Barren Grounds or Cold Desert. T-^-^<i-^'^ 



7. The Alpine Deserts. 



A mere inspection of this list of avian and vegetational formations 

 shows that the recognition of these large environments is relatively 

 simple. It is also seen that they represent fairly definite physical 

 or environmental complexes of such fundamental importance that 

 there can be no doubt as to their general validity. As to the relative 

 value, influence, boundaries, and the dynamic relations of these 

 formations, much is already known, but not as an organized body 

 of facts and principles. It will also be noted that these regions do 



