Abstract: This paper describes the significant changes of forest biological structcure,succeeding from sparse purepine forest to pine-shrub mixed forest and to multi-layer pine-broadleaved mixed forest communityduring three decades of closing mountains and rearing forests. The Natural parasiting rates of 1st-3rd generations of Dendrolimus puncts are respectively increased by 41.09-67.49%,which devastates the e-cological conditions for larvae growth and development and greatly reduces the infestation of DendrolimusDuncts. A relatively stable and balanced forest ecosystem is the key for comprehensive cortrol of insect pests.

Key words: OCPs, PCBs, residue, sediment, ecological risk.