Further to the Hydrologic Importance of Transpiration Control by Stomata

An exchange of views on the above subject [ Idso , 1968; Lee , 1968] revolves principally around results of several experiments carried out by me and former colleagues. Some clarifying comments appear in order, since all relevant details were not published. A general view must admit that, together with a number of internal and external conditions, leaf stomata determine the rate of transpiration. From a hydrologie or an engineering view, however, what matters is whether this role is of consequence. The issue can be settled only by a study of the transpiration from naturally exposed canopies of vegetation, of their atmospheric environment and, simultaneously, of the transpiration resistance of the leaves. Generalities derived from theoretical or simulation studies cannot supply the answer, and I agree completely with similar comments made by Idso [1968]. Experiments in which vegetation is wetted by rain or artificially cannot be used as evidence, unless the complete energy balance is simultaneously studied. Experiments involving singly exposed individual plants cannot inform us by simple analogy about the transpiration of natural stands.