A Functional, Factorial Approach to Plant Ecology

Plant ecology is concerned with interrelations of plants and their environments. This paper proposes a scheme for considering the qualitative aspects of these interrelations with some rigor and completeness. It also makes such interrelations amenable to quantitative treatment. The proposed scheme is based on the theory that specific environmental factors exist and that they determine the characteristics of vegetation. This theory, implicit in plant ecological literature, can be elaborated to explain some of the empirically determined propositions and concepts of plant ecology. The concept "interrelations" used by ecologists can be interpreted as the concept "function" used in quantitative science. The two ideas are basically one. Therefore, this paper approaches plant ecology as the study of the mathematical functions which relate vegetation to its environment. More precisely, these mathematical functions relate the specific properties or characteristics of vegetation to the groups of factors which we conveniently call "vegetation determining factors." The methods and scheme suggested here may appear to contradict the holocoenotic belief exemplified by Cain's (1944: 19) statement: ". . . the complex interrelations among the environmental factors, and between them and the organism, with its complex physiological and morphological interrelations, are such as to defy solution in exact terms of causation. Ecological problems not only may be difficult of solution because of the interaction of factors and responses, but they may really be insoluble in a mathematical sense." However, the approach proposed here stresses only that the establishment of quantitative functional interrelations in plant ecology is possible, provided one restricts the study to causation between vegetation and environmental factors (groups of factors determining vegetation) and deliberately omits the causes of variations in the environmental factors themselves. Causes of variations in the environmental factors are considered to be parts of such sciences as climatology, geology, geomorphology, pedology, anthropology, human history, organic evolution, and historical plant geography; they are left outside this treatment of plant ecology. In an etymological sense these sciences are ecological, but they are not considered plant ecology-which is the subject of this paper. Solution of quantitative interrelations of vegetation and environment can be developed along the line Jenny (1930, 1941, 1946) used for the examination of soils in relation to environment. The basic thought of this paper and many specific ideas in it stem directly from the approach to soils used by Jenny. The writer very gratefully acknowledges this primary debt, the active encouragement Dr. Jenny has given to expansion of his own ideas, and his help on this manuscript. Discussions among Drs. H. Jenny, R. L. Crocker, and N. C. W. Beadle in 1949, which considered some of this paper's points, were attended briefly by the writer who appropriated the mutual conclusion identifying the flora as the independent aspect of the plant cover; vegetation as its dependent aspect. I wish to thank all three men for criticisms and opportunity for discussion. However, they should not be blamed for the following presentation, and it is not implied that they agree with it.