Abstract
In tree planting constructions and tree management works, we have used the rank appraisal method by the Resources Council in the Science and Technology Agency to evaluate tree vigor. However, this evaluation method has a weak point about the change of results due to personal factors. Consequently, an objective method has been needed. The new evaluation method for tree vigor, the relative change of sap temperature, was proposed using the degrees of changes that sap temperature was fluctuated by heat exchanges between the tree and its external environments. In this study, we investigated the net radiation on the surface of stems and the vertical changes of temperature in the stems for the vital and weak trees. When the transpiration is active in the almost same thermal environment such as air temperature, the degree of tree vigor related to the transpiration can be almost judged by the relative change of sap temperature calculated from some tree stem temperatures and etc.. And it is obvious that the relative change of sap temperature has some physiological meanings.
