. Plant succession; an analysis of the development of vegetation. Plant ecology. 374 PAST succession: the cenbosere. the coniferous belts of the north and of the mountains were even then more or less dijEferentiated into two climaxes as at present. The advance of the ice was doubtless more or less pulsatory, but we get perhaps the clearest picture of the course of the clisere if we assiune that the ice gradually overwhelmed the timdra zone, and at the same time changed the conditions in the bog-scrub zone in such a way that they became unfavorable for shrubs and favorable to the herbs, mosses,
. Plant succession; an analysis of the development of vegetation. Plant ecology. 374 PAST succession: the cenbosere. the coniferous belts of the north and of the mountains were even then more or less dijEferentiated into two climaxes as at present. The advance of the ice was doubtless more or less pulsatory, but we get perhaps the clearest picture of the course of the clisere if we assiune that the ice gradually overwhelmed the timdra zone, and at the same time changed the conditions in the bog-scrub zone in such a way that they became unfavorable for shrubs and favorable to the herbs, mosses, and lichens of the tundra. At the same time, perhaps. (i;^ Tundra Iggl Scrub Evva Deciduous Foresi [inrai Conifers(Northcrn) tv?^ ConifersCSouthem) Fig. 36.—Ice-mass and cliseral zones in front of it during a glacial epoch. Slightly modified from Transeau. because of the general deformational sequence as much as the influence of the ice, the factors of the coniferous belt became less favorable to trees and more favorable to shrubs. How soon this influence was felt in the deciduous climax is largely a matter of conjecture, but sooner or later colder or drier conditions appeared there as well. In consequence, migration to theXsouth- ward alone was capable of securing the preservation of each zone. The parent individuals and the migrants in all other directions were eliminated by compe- tition with the newcomers from the north, by the direct action of the colder climate, and ultimately by the destructive action of the ice itself. As a con-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Clements, Frederic E. (Frederic Edward), 1874-1945. Washington, Carnegie Institution of Washington
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