Abstract: Global change has been received more and more attention for the decades, Coz concentration in the atmosphere has been increasing at a much faster rate than that has been observed in the historical record. Scientific evidence from long-term monitoring had revealed the creeping destruction of ecosystems upon which human existence depended. Recognition of this destruction has impelled to changing international policies used to manage our planet. A lot of research on terrestrial ecosystems and global change have been done. However, they were mainly concentrated on the responses of terrestrial ecosystems to global change, the studies on the feedback of vegetation on climate have been seldom done. The study on the effect of vegetation on climate would enhance the understanding of global change, and promote the accuracy of evaluating and predicting the responses of terrestrial ecosystems to global change. The authors would discuss the feedback of plant on climate based on the two well-known balance equations. There are two well-known balance equations on the earth’s surface. For long period, such as year, heat balance equation expressed as Rn = P+LE and water balance equation expressed as r=f+E, where Rn designates net radiation; P. sensible heat; LE, latent heat: r, precipitation; f, runoff; E, evapotranspiration. Therefore, the difference Af between fa and fo (after and before the surface change respectively) could be expressed as △f = fa–fo = (L△r–△Rn + △p)/L △ f= –2. 7 × 10–5 g/(cm2· min), △θw = –0. 05 ℃. then the effect becomes negative. These results indicate that the effect of plant on temperature depends on specific area. If △θw=0, that is to say, the effect of plant on temperature for the loess plateau is zero, △f = 5△a × 10–4 g/(cm2· min) This result also indicates the reason why the relationship between the surface temperature on forest surface and on cut forest surface is uncertain. In a word, the effect of vegetation on climate deponds on specific regions. Vegetation has the function of reducing run off. The effect of vegetation on precipitation may not be considered. This paper provides a long-term and region-scale based method for evaluating the effect of vegetation on climate.

Key words: Vegetation, Climate, Feedback