Research On Charecteristics Of Degraded Forest Ecosystem And Its Restoration Countermeasure In Sub-alpine Of Northwest Yunnan

Forest ecosystem restoration and reconstruction in subalpine region is always a hot and difficult research point through the world. Subalpine cool-temperate and cold-temperate forest is the most typical vegetation type at the "Three Parallel Rivers" area in northwest Yunnan with characteristics of ecological sensitivity and vulnerability. This study choos Shangri-la located at core zone of northwest Yunnan as study site. Based on the physiognomy of communities, four vegetation types of wasteland (extreme degradation), shrub-grass land (heavy degradation), open forest (medium degradation) and Larix secondary forest (light degradation) were selected to present different degraded forest communities. Where as, Quercus aquifolioides primary forest (none degradation) is chosen as the control for the study. Within the five degraded communities, sample method was adopted to study the community characteristics. Main ecological factors were determined and recorded. The soil samples were collected and the physical and chemical properties were analyzed. The soil seed bank was studied by applying greenhouse germination method, the seed rain was investigated using basket collection method. Finally, based on the studying results of characteristics for each degradation indicator, restoration countermeasures for degradaed forest ecosystem in northwest Yunnan were proposed. The study findings are as follows.1) As the reduction of degradation gradient, the height of community gradually increase, the species richness showed the tendency of first increase and then decrease in none degradation. The species composition changed in community follow the direction of grass-shrub-tree. The pioneer species gradually decreased and disappeared, the characteristics of species showed the change from heliophilous, neutral to shade. As far as the life form was concerned, in the sites with higher degradation gradient, hemicryptophyte was dominant, while in lightly degraded sites, the proportion of hemicryptophyte obviously decreased and the percentage of meso-phanerophytes and micro-phanerophytes significantly increased. From extreme to non-degradation, the diversity index of grass layer showed the tendency of decrease, the diversity of shrub layer showed the tendency of first increase and then decrease, while the diversity of tree layer gradually increased.2) With the alleviation of degradation, the solar radiation within the forest community decrease and the soil moisture increased, the air temperature, land surface temperature and soil temperature decreased. The small the variation range of ecological factors was, the stable the environment would be, and would result in favorable rowth condition and vigorous development of plants.3) With the alleviation of degradation, the soil physical properties developed in the favorable direction, characterized by decrease of soil bulk density and increase of porosity, moreover, the chemical properties showed the tendency of increasing, which reflects the recovery process of degraded forest community was also the coevolution process of soil environment.4) The number of species in seed bank ranks as light degradation> non-degradation >extreme degradation>medium degradation> heavy degradation; the rank of seed density is extreme degradation> medium degradation>light degradation>none degradation> heavy degradation. Generally, as the decreasing of degradation, both species composition and density of seed rain appeared the tendency of increaseing. The Jaccard similarity coefficient between seed bank, seed rain and ground vegetation was relatively low. Although, the contribution of soil seed bank to regeneration of aboveground was small, it still had a very important potential impact on restoration of disturbed vegetation. Seed rain played an obvious role on the revegetation for both medium and light degraded forest ecosystems.5) Among degradation indices, the average variation rate of tree layer diversity index, available P, shrub layer diversity index, phanerophytes proportion, tree layer height, total N and organic matter among 5 degradation gradients exceeded 40%, which had highest indicative ability, were recommended as major indicators to present the degradation conditions and more attention should be paid in restoration activity in subalpine northwest Yunnan.6) The countermeasure for restoration of degraded forest ecosystem in subalpine northwest Yunnan was suggested as taking "close to nature forestry" theory as guidance, adopting native tree species, implementing the technologies of mixture plantation and promoted natural regeneration to recover biodiversity, enhanced forest productivity and achieved harmonic development of social economy.