RELATIONSHIP BETWEEN ACID RAIN AND THE DECLINE OF A MASSON PINE FOREST IN NANSHAN, CHONGQING
重庆南山酸雨与马尾松衰亡的关系

The decline of a masson pine forest of some 2,000 ha located on the south bank of the Yangtze River near Chongqing were investigated. The results of rain water monitoring for four months indicated that the frequency of acid rain was 100% and the average pH of the rain water ranged from 4.2 to 4.4 with minimum observed values around 3.6 to 4.0, which caused a drop of forest soil pH to a range of 3.7 to 4.0. The contents of Mn and Co in the needles of dying trees decreased significantly,together with a decrease of soil contents of these elements, while A1 content in the needles accumulated to a level three times higher than that of normal. The acid rain in the area is obviously the main reason causing the decline of the forest.