Abstract:

With the interpreted IKONOS4 satellite images collected in 2005, a 1∶10 000 forest map, the data collected in Class II forest survey in 2007, and surface runoff data obtained in the permanent runoff monitoring station, six site factors of slope gradient, slope position, soil thickness, soil thickness of A layer, soil type and soil water content were selected to establish a matter element model suitable to 297 forest sub-compartments. Further, the AHP was applied to modify the spatial structure and form the spatial para allocation of the protection forest system. The results showed that:1) the area allocation of different vegetation types was irrational, the area of a mixed coniferous and broad-leafed forest was 124.39 hm², accounting for 14.97% of the forested land,the mixed forest was consisted of two coniferous species accounted for 27.37% of the total forest land, and the pure forest was consisted of one coniferous species accounted for 42.48%. 2) After optimization, the area allocation of different vegetation types in the protection forest system ranked as:the mixed coniferous and broad-leafed forest (31.12%)＞shrub land (15.5%)＞the economic tree crops (12.28%)＞the mixed forest consisting of two coniferous species(11.46%)＞the pure broad-leafed forest(11.41%)＞the pure coniferous forest (9.51%)＞grass land (8.70%). Besides, the annual surface runoff could reduce 43 171 mm or 62.15%, annual soil erosion could decrease 465.97 t or 79.66%. 3) The following suggestions for spatial para allocation of the small watershed protection forest system were proposed:① reducing pure cypress or pine forest, and increasing alder-cypress, oak-cypress or pine-cypress mixed forest. As for the current cypress and pine pure forests, alder or oak could be introduced to develop a mixed forest. ② The canopy closure of pure cypress forest and alder-cypress forests should be maintained within 0.60-0.75,and the canopy closure of oak-cypress, pine-cypress or oak-pine forests should be controled within 0.6-0.8. ③ For improvement of current pure coniferous forests, an opening and beating-up method and the density regulation could be applied. For the opening and beating-up operation, strip cutting and replanting of broad-leafed species, such as oak, alder and camphor, could be applied. ④ For enrichment of species composition, the mixture ratio should be based on the specific site condition and tree features. In the neutral or minor acid purple soil, mixed cypress forest would be favorable; in the yellow and acid purple soil, cypress-broad-leafed or pine-broad-leafed forest would be suitable. In the grey sand soil, pine-broad-leafed forest could be dominated, and the broad-leafed species could reach to 20%-30%, even 40% in favorable sites.

Key words: matter element analysis, analytic hierarchy process, Guansi river watershed, protection forest, spatial para allocation, structural optimization