Interior North America Research Articles

Glacial and Post‐Glacial Plant Migrations Indicated by Relic Colonies of Southern Ohio

The vegetation of all glaciated regions, and of unglaciated lands close to the glacial boundary, has become established after a series of migrations incident to climatic changes and natural invasion and competition in the vast denuded territory. The vegetation of today, in its unlike components, reflects these migratory waves. Relic colonies-groups of plants unlike those of the surrounding and dominant vegetation, but belonging to some more distant formation-remain as evidence of past conditions. Recent field work in southern Ohio has disclosed a conglomeration of unlike plant communities, communities representing distinct types of vegetation and even different climatic formations. As these are not sucessionally related, or only slightly so, it becomes necessary to consider them in the light of past migrations of the glacial epoch and early post-glacial times. While pre-glacial history of floras must be built almost entirely upon geographic distribution and relationships of species, and upon fossil remains, glacial and post-glacial history depends largely upon relationships of communities. Thus relic colonies-isolated bits of vegetation-become very important in tracing migrations. Such relic colonies are scattered all over North America. They are abundant in regions near the southern boundary of continental glaciation and on some of the drift deposits-anywhere, in fact, where vegetation was affected either directly or indirectly by glaciation. The region under consideration-southern Ohio-includes unglaciated territory as well as glaciated land of three ages, Illinoian, Early Wisconsin and Late Wisconsin (Fig. i). In the unglaciated land, it is doubtful if the forests were ever completely displaced. They are, then, a direct development of the earliest forest of interior North America.

Two petrified palms from interior North America

Two petrified palms from interior North America