Water Relations and Chlorophyll Content of Forest Herbs in Southern Wisconsin

Abstract

Many investigators have presented the results of studies concerned with differences between sun and shade plants. In most instances, the heliophytes (sun plants) are those which normally grow in full sunlight, while the sciophytes (shade plants) are those which grow in very dense shade, Oxalis acetosella being a favorite. These studies have been conconcerned with such characteristics as leaf morphology and anatomy; transpiration, respiration, and photosynthetic rates; pigment concentration, development of conducting system, osmotic value of cell sap, and water relations. These earlier studies have dealt, in the main, with species which are radically different in that they reach optimum development in either bright sunlight or in very dense shade. The present paper, on the other hand, is concerned with a comparison of the species characteristic of several portions of the upland forest continuum in the prairie-forest border region of Wisconsin. This continuum is a lineal arrangement of forest stands which embraces the gradient from the pioneer forest stages, with their high light intensities, immature soils, and variable moisture conditions to the climax forests with their extreme shade, mature soils, and constant, abundant moisture conditions. The continuum index, which ranges from 300 to 3000, locates any given stand along the continuum. The writer wishes to express his appreciation to Dr. John T. Curtis for suggesting the problem and for helpful advice and criticism throughout the study as well as in the preparation of the manuscript. LITERATURE REVIEW