| The objective of the work probed into and opened out the theory and the related laws of tree growth and nutrient balance and site productivity of maintenance in the area of Eucalyptus plantation and its degradation site management. By expatiating and validating, it made clear some topics such as the ecological harvest age and season of Eucalyptus, the importance of tree fertilization and the stage of nutrient uptake and the change of nutrient pools of tree parts, the age and spacing effect of the increasing spacing and the mixed measure on productivity, nutrient distribution and site maintenance, the restraining mechanism between the mixed species and its control. The management model of Eucalyptus plantation, finally, was put forward. Main results and conclusions are as follows:1. Leaf litter, the main contributor of the total annual litter fall, has a rhythm with double peak curve. Reacted with the lower temperature and lower precipitation, canopy competition accelerated the amount of branch and leaf litter fall, which was the lowest as canopy spread. Trees should be harvested after the peak times of season and tree age to return nutrient via litter partially.2. The order of significant difference of tree parts for N-concentration was leaf > branch, bark, root > bolewood, for P leaf > branch, bark > root > bolewood, and for K leaf > bark, branch > root. NPK concentrations, generally, decreased with increasing tree age, the age effects of which were significant on branch and leaf so as to reveal the major role of forepart NPK managements. Trees with same age had almost stable nutrient concentrations. The total nutrient pools per hectare increased with increasing tree age. Three significant difference stage of nutrient uptake of Eucalyptus during one rotation could be divided.3. The proportion of the dry weight of leaves that had small change after 2.5a to total biomass of tree parts decreased with increasing tree age, in reverse to bolewood weight. NPK pool treads of aboveground biomass before 2.5a could be used to account the ratio of nutrient supply, in rapid accumulation of NP before 3.5a. Eucalyptus fertilization was main approach for returning nutrient from exterior setting in order to ensure a balance nutrient system in forest soil. New concepts of the site nutrient losing (SNLo) and the site nutrient lacking (SNLa) were put forward. Amount of SNPLo was equal to that of nutrient for preventing site degradation, SNLa for maintaining site productivity. The essential of site degradation was result from SNLo increasing.4. Spacing effect had the facilitating effects on mean diameter, height and biomassof trees. The mixed stands, Eucalyptus ABL12 X Acacia crassicarpa Cunn, was restrain Eucalyptus growth and Acacia, the mechanism of which was from the no-stratification competition of canopy that lead to reduce the utilization efficiency of light resources, and from soil micro-environment of the no-cooperation and no-supply each other of fine roots between the mixed species.5. Increasing spacing added the biomass of tree parts, especially leaf and root, and relatively reduced the proportion of the allocated biomass to bolewood. However, the mixed measure increased the weights of a tree and per hectare leaves while decreased that of other tree parts, especially for branch, no effect on root biomass. Increasing spacing had more significant effect on leaf biomass than the mixed measure.6. The mixed measure increased the amount of litter than monoculture and enlarged the period of fall and increased the leaf litter but reduced the branch litter. With higher bioactivity, the mixed measure had a more positive effect on soil fertility parameters.7. The mixed measure and increasing spacing separately increased the NPK contents and pools of leaves and roots; however the former had more adding effects on that than the latter. The mixed measure reduced the PK contents and pools of tree parts except leaf,8. Increasing spacing increased average NPK concentrations of a tr...
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