Forest Centers of Eastern America

Abstract

It may be stated, by way of summary, that eastern North America is occupied by four great forest centers: (1) the Northeastern Conifer forest, centering in the St. Lawrence basin, (2) the Deciduous forest, centering in the lower Ohio basin and Piedmont plateau, (3) the Southeastern Conifer forest, centering in the south Atlantic and Gulf coastal plain, and (4) the Insular Tropical forest of the southern part of the Florida peninsula, centering in the West Indies. The term center as here used, implies the idea of distribution about a region where the plants attain their best development. Such vegetation divisions are not fixed, but move and increase or decrease in extent depending upon continental evolution and climatic change. Each formation is made up of many societies, bearing a definite successional relationship to one another, which being dependent upon soil factors may be best correlated with physiographic changes. In regions intermediate between centers, the local order of succession is made up of societies from each of the adjoining formations. It has been found that if the ratios produced by dividing the amount of rainfall by the depth of evaporation for the same station, be plotted on a map they exhibit climatic centers which correspond in general with the centers of plant distribution. Further, the distribution of grassland, prairie, open forest, and dense forest regions is clearly indicated. This is explained by the fact that such ratios involve four climatic factors which are of the greatest importance to plant life, viz temperature, relative humidity, wind velocity, and rainfall.