The Monitoring of dynamic change of forest area in tropical forest vegetation of Xi-shuangbanna Prefecture has been discussed in this paper. There are of two parts being included:1

Using multkemporal remote sensing imagery to interpret forest area change of Xi-shuangbanna Prefecture.In monitoring of the forest area dynamic change

used of multitemporal remote sensing imagery are: （1） aerial photographs Feb-1965; （2） Landsat MSS 02-Mar-1973; （3） aerial photographs Feb-1981; （4） Landsat TM 02-Feb-1988 and Spot XS 16-Feb-1988.According to multitemporal remote sensing imagery interpretation

the forest area in 1965

1973

1981 and 1988

of Xishuangbanna Prefecture have been calculated. Results from calculation showed that about 33.72% of the total area of Xishuangbanna Prefecture is covered by tropical and subtropical forest in 1988. But

according to the interpretation of aerial photographs of 1965

the forest area was 46.46% of the whole Prefecture. The comparison of the forest area showed that the decrease rate is about 0.55% per year.2

Using difference imagery to analyse forest area change of nature reserves.Forest area change in nature reserves has been studied by means of digital analysis of Laudsat MSS （1973） and TM （1988） images. An unsupervised classification consisting of principal components analysis fllowed by a clustering procedure was adopted. The normalized difference vegetation index （NDVI） was used as a measure to assess the change in vegetation amount.It was provisionally concluded that degradation of forest area have ceased inside the nature reserve

while outside the nature reserve boundaries

forested area have decreased significantly.The results showed that this method was effective and could be extensive used in renewable resources especially forest vegetation monitoriing.