Frederic E. Clements

Nature and Structure of the Climax

NATURE OF THE CLIMAX .254 Unity of the climax .254 Stabilisation and change .255 Origin and relationship .257 Tests of a climax .257 CLIMAX AND PROCLIMAX .261 Essential relations. 261 Proclimaxes 262 Subelimax .262 Disclimax 265 Preclimax and postclimax. 266 Preclimax 267 Postclimax .269 STRUCTURE OF THE CLIMAX .270 Community functions. 270 Roles of the constituent species: dominants 270 Influents . .271 Climax and seral units . .271 Climax units . .272 Association ..273 Consociation ..274 Faciation ..274 Lociation .. 275 Society ..275 Sociation ..276 Lamiation ..277 Sation ..277 Clan ..278 Seral units . .278 Serule ..280

The Vegetation Regions of the Prairie Province

THE vegetative covering of the North American continent falls naturally into two great areas, forest and plain. At first thought it would seem that these were primary phytogeographical divisions, but a comparison with the vegetative covering of other continents proves the contrary. Considered as a phytogeographical feature, the North American forested area is an entity; from a floristic or formational standpoint, it may be analyzed into several distinct portions of widely separated relationship. The ground-tone of the great bulk of the North American forests is that of the forests of British North America, which are closely-related to those of middle-north Europe and Siberia, constituting with them the northern realm of Drude and the sub-arctic region of Engler. Three great belts extend southward from this northern mass, each undergoing profound changes in type, and becoming differentiated into well-characterized regions. The floristic separation of these regions from the northern forest-region is so great that the relationship is always much less close than that existing between the floral covering of British America and that of northern Eurasia, and in one or two cases it practically disappears. The forests of Mexico and Central America are tropical, or subtropical, and are both