The purpose of this study was to measure quantitatively the effectiveness of precipitation by determining the amount and timing (i.e. distribution-in-time) of plant absorption of moisture during the summers of 1965 and 1966. In addition the effectiveness of precipitation was related to some causal factors, especially those factors which help provide a procedure for calculation of this effectiveness.

The sand dunes lying ten miles northwest of Kanab in Kane County, Utah, support a sparse plant cover with four species dominating the vegetation: Psoralea stenostachys, Sophora stenophylla, Oryzopsis hymenoides, and Wyethia scabra var. attenuata. Of these Psoralea and Wyethia are endemic to the dunes or to a limited area which includes the dunes. The pineer species gain a start in the valleys between dunes and occupy the area only until sand covers them or until sand is blown away from their roots. Stabilization of the soils is not permanently in the interdune valleys and the dunes continue to wander. The low fertility of the soils, the low moisture content, the extremes of temperature, light, and other environmental factors limits the number of individual plants which can occupy the dunes. The region will continue to have actively moving dunes until major climatic changes occur permittimg a denser plant cover which would tend to stabilize the sands.