130 MICHIGAN SURVEY, 1908. 



that the science of plant ecology and many of its general principles and 

 methods are applicable to birds. A general knowledge of plant ecology 

 is therefore becoming one of the most valuable tools in the hands of the 

 field ornithologist. Every field naturalist has observed the general cor- 

 relation of certain birds with certain kinds .of vegetation. This rela- 

 tion is clearly expressed by Ridgway ('89, p. 8) as follows: "There 

 is probably no better index or key to the distribution, of birds in any 

 country than that afforded by the character of the vegetation; should 

 this • vary essentially within a given area, a corresponding difference 

 in the bird-life is a certainty." This phase of tie subject clearly illus- 

 trates the oft-repeated experience of naturalists that in order to thor- 

 oughly understand one subject — perhaps the favorite one — it becomes 

 necessary to study another, or even several. Thus ini order to know 

 the bird life of a region it has become necessary to study the ecolo- 

 gical relations of its vegetation. 



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, who needs primarily to know the major plant as- 

 sociations or fonnations and their successional relations. This im- 

 plies ability to recognize dominance among plant species and the gen- 

 eral 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 pre- 

 vail over a large geographic area in the last stages of mutual adjust- 

 ment of all environmental and biotic processes. Such an association 

 or formation tends to occupy such an area to the exclusion 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, grassland 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 formations 

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

 evident oomithological utility. The following may be recognized pro- 

 visionally : — 



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 Forest of Eastern Canada. 



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



6. The Barren Grounds or Cold Desert. 



7. The Alpine Deserts. 



A mere inspection of this list of avain 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 prin- 



