| The Mountainous Area in Southwest Sichuan is situated in Jingsajiang River Valley in the upper reaches of Yangtze River, which lies across Hengduansan Mountain Range, so it is located in an important zone of the water conservation forests in the headstream of the Yangtze River, with an outstanding ecological position. Since complex influences of Southeastern Monsoon and Southwestern Monsoon and the variation of the mountainous climates, the vertical hydrothermal condition on landforms varies obviously. According to the characteristics of geography landscape and of forest ecosystem, the fragile eco-regions difficult to restore forest vegetation include: dry-hot valley below elevation 1500m, and distribution region of arid evergreen hardwood forests and Yunnan pine forests with elevation 1500m-2000m. Therefore, focused on the problems of vegetation restoration and forest regeneration restoration of the two regions above, this research will be carried out. The dry-hot valley is the typical region difficult to afforest and restore, with worsen eco-environment, serious artificial interferes and deteriorate habitat, according to natural succession theory, relying only on natural restoration, it takes a long time and makes too slow progress and low effect. The former researches were over-restricted by national checking standard of afforestation, the ecological course of vegetation restoration has been overlooked, so the effective technologies have not formed, effect of afforestation was low. Therefore, to accelerate the ecological restoration of vegetation, the research on vegetation restoration technologies mainly with afforestation in dry-hot valley is the hot point focused by science circles now and then. The arid evergreen hardwood forests and Yunnan pine forests, distributed mainly in the upper edge of dry-hot valley, have been influenced by harvesting for a long period. With more and more arid eco-environment, natural regeneration effect of forests is influenced seriously, so the upper edge of dry-hot valley is moving up, forests is in degraded state and forms the low effect forest of low density. Therefore, it is an urgent need to regenerate and recovery and to study on forest natural regeneration mechanism, that is, on the feature of soil seed bank and seed rain. The technical measure of effective regeneration restoration will be put forward, and it offers technical reference and guidance for natural forest protect project. Now, researches on ecological restoration of forest vegetation in mountainous region is concerned seriously, but researches on the ecological mechanisms of forest vegetation restoration are comparatively less, therefore, the research on ecological restoration mechanism of mountainous forest in eco-fragile region in dry-hot valley and its upper edge will be carried out, using the principles such as Ecology, Restoration Ecology, Physiological Ecology, etc.1. Aiming to the key problem degraded ecological environment and difficult to recovery vegetation in dry-hot valley of Jingshajiang River, with the center of soil moisture, from the angle of plant physiological ecological and soil equilibrium, using theories of ecological bearing capacity and ecological water-utilizing, by a plenty of tests, the mechanisms of "appropriate" afforestation in dry-hot valley are further discussed. (1) By investigation of climate factors (precipitation and evaporation) of the different elevation gradient in vertical profile of dry-hot valley, the arid duration in dry-hot valley is as long as 7 months (from November to May of later year), in arid duration, farmland water loss is much more and annual lose reaches near 800 mm, water surface evaporation reaches more than 8 mm daily. (2) By studies on moisture content of mountainous gritty red soil, mountainous yellow red soil, mountainous carbonate dark red soil and mountainous red calcareous soil, the results showed, alternating arid season with rain season is obviously and arid duration lasts a long time, there are 6 months in one year when soil moistu...
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