THE STRUCTURAL CHANGES OF CUNNINGHAMIA LANCEOLATA HOOK. COMMUNITY EXPOSED IN COMPOUND-POLLUTED ENVIRONMENT FOR A LONG TERM

Cunninghamia lanceolata Hook.forest exposed in compound-polluted environment for long period was investigated and its structural changes were analyzed by comparative study with the normal forest in the same afforestation site,technique and time in this paper.Some interesting conclusions were drown.Under the compound polluting stress for a long term,tree layers of the forest occurred unfavorable spatial decline.Both the average height and diameter at breast height(DBH) decreased 4.14 m and 3.96 cm respectively.The density and coverage also reduced 7 stems/100 m² and 25% respectively.Cunninghamia lanceolata population grew weakly. Ascribing to the tree population declining,understory habitats were so profitable for shrubs that their density and coverage increased 43 stems/100 m² and 35% respectively.Herbs kept relative stable.To make interesting,species compositions had obvious differences,especially in tree layer.Many deciduous broad-leaf trees implanted and colonized successfully, and this changed Cunninghamia lanceolata forest into uneven aged,broad and conifer leaves mixed forest from even-aged and conifer pure forest,and being changed into broad-leaf forest.It inferred that those broad leaf trees,including Sassafras tsumu,Lindera glauca,Quercus variabilis,Betula luminifera, Populus sp.,Symplocos sp.etc.,may be the most suitable species of restoring and reconstructing forest after Cunninghamia lanceolata forest degraded. Totally speaking,the long term stresses of compound pollution made Cunninghamia lanceolata forest have higher species diversity index and community evenness and lower ecological dominance,implying the long term stresses of compound pollution guided Cunninghamia lanceolata forest developing to complicate direction and on normal succession's way.