Abstract: The relative fatness of brand's voles was calculated by empirical formula. The results indicatedthat relative fatness becomes less as the age grows.There were no significant sexual differenceswith respect to relative fatness,But seasonally it was high in spring and decreased in summer,then the highest in autumn and decreased in winter. Variations of relative fatness were closelycorrelated with population density and breeding.

Key words: poplar, canopy conductance, sap flow, Granier’s probe, environmental factor.