| Based on the analysis on the converse succession of vegetation in degraded ecosystems in dry-hot valleys of Yunnan, a fixed site study on artificial vegetation restoration and human assisted vegetation restoration were conducted for 4 years in the experimental area located in a typical dry-hot valley of Jinsha River, Yuanmou, Yunnan Province. The study suggested that environmental stress and plant resistance were the key factors that affected community stability and optimization of an ecosystem, clarified the interaction of community and environment was vital for vegetation restoration or reconstruction in degraded ecosystems in Jinsha River dry-hot valleys. The objective of the study was to provide with a science support for the vegetation restoration for degraded ecosystems in dry-hot valleys in Yunnan. The main results were given as follows:(1) Meteorological factors were studied in the experimental weather station to find out their roles in vegetation restoration in degraded ecosystems of dry-hot valley. It suggested that low and unevenly distributed rainfall, sufficient light, high temperature and evaporation, low air humidity made jointly vegetation restoration in dry-hot valleys very difficult.(2) A comparison study was conducted to study the impacts of restored vegetation on microclimate. It's results showed that ①There was variation on soil temperature inside and outside forests ,and the time for temperature variation to occur lagged downward the soil. ②The relative humidity did not differ too much in dry season inside and outside a forest. ③ Evaporation outside forest was higher than that inside forest.(3) Soil surveys was conducted to study the soil distribution, soil properties and fertility. It suggested: ①The dry -hot valleys had a great variance in soil types.② The poor soil structure, relatively high volume density, and poor water holding capacity were common for soils in dry-hot valleys ③ The soil water contents differed clearly from rainy season to dry season. Water contents were greatly different under different site conditions. ④The soil temperature in the hot-dry valley was relatively high, heat was conducted from surface soil downwards in daytime and from deeper soil upwards in nighttime;(5) The compact and dense soil in hot-dry valley resulted in poor soil water infiltration .The infiltrations of soil with different vegetations followed a sequence based infiltration velocity at initial stage: Pinus Caribaea+ Dodonaea wiscosa mixed forest > Pinus Caribaea pure forest>Albizzia kalkora forest >Eucalyptus forest > Tephrosia candida+ Dodonaea wiscosa mixed forest> barren land>expansive soil.(4) Physiological and biochemical factors like light absorption, energy conversion and use efficiency etc for plants subjected to water stress were studied. The results suggested that: ①The noon break of photosynthesis for tested Dodonaea wiscosa was mainly caused by a non-stoma limiting factor —photoinhabition that was a protection mechanism against damage to photosynthesis organs;② The tested Dodonaea wiscosa maintained a basic photosynthesis level when subjected to severe water stress, reaching a very high Pn value when PAR not less than 1300 umol.m-2.s-1 .Which indicated indigenous species had great adaptability to high light intensity and water stress .(5 ) The drought resistance for plants was tested using 8 physiological andbiochemical parameters of leaf water content, relative conductivity, MDA n SOD > POD,fluorescence, chlorophyll content and Pro. The results showed that: ?Seedlings of indigenous Radonea wiscosa, and Tephrosia Candida were relatively more drought resistant to water stress;? When subjected to water stress PSII in the leaves of indigenous Radonea wiscosa still maintained a relatively high photochemistry activity;? When subjected to water stress, photosynthetic pigments inside the leaves of Radonea wiscosa were more stable than those of Leucaena leucocephala and Tephrosia Candida, the photosynthetic pigments of Radonea wiscosa was more resistant to water stress;@ When subjected to water stress, proline content,soluble sugar contents and potassium ion were increased , turgor pressure of plants was maintained at a certain level Therefore physiological processes like cell growing, stomata opening and photosynthesis were kept going on. (5) MDA content of leaf for tested species was affected by water stress. (6) Water stress increased relative conductivity of tested species at varied degree, the increases for leaf from Radonea wiscosa and Pistacia weinmannifolia were smaller and slowly, suggesting their membrane maintained normal for a longer time and less injured when subjected to water stress. ? Subordinate function values based on leaf relative water content, relative conductivity, MDA> SOD> POD, fluorescence, chlorophy content and Pro were used to assess drought resistance of tested species. The species were listed from high drought resistance to low as: Radonea wiscosa, Pistacia weinmannifolia, Leucaena leucocephala and Tephrosia Candida.(6 )The analysis on succession kinetics of vegetation was conducted using a model based on the theory of dissipativity structure and theory of heterogeneity. The results showed that:? The community succession of the degraded ecosystem in hot-dry valleys in Yunnan was an embodiment of a dissipativity structure. There were exchanges on energy and information between vegetation communities and their environments. The succession might be towards either deterioration or restoration. ?Entropy theory was of great application value in analyzing vegetation succession in degraded ecosystems of dry-hot valley in Yunnan. Entropy values could be applied to assess the structure characteristics and succession tendency of vegetation communities.? During the course of vegetation restoration in dry-hot valleys, the entropy was decreased and the order was increased. The fact suggested the ecosystem's structure and functions became better, a plant community and its environment could be optimized.(7) The study on hydrological factors and their impacts on vegetation restoration indicated: ? In rainy season soil water content in barren land was higher than in forest land. Because of the shield effect of forest, hysteresis was found in forest land. ? Stem flow was determined by the area of direct effective water intercepting surface on the stem. (3) The clayey soil in the hot-dry valley easily resulted in ground runoff. Besides rainfalls were highly concentrated and intensified, so ground runoff coefficient on a slope was relatively higher. @ Owing to the successful vegetation restoration in the experimental area with coverage over 60%, only small quantity of runoff was collected in plots and the volume measured at the general outlet of the catchment was also small.(8) Soil erosion in relation to vegetation was conducted by setting up plots and long term monitoring. The results showed: ?The dry-hot climate, long history of humandisturbance, and sparse vegetation resulted in severe desertification in dry-hot valleys. (2) The experimental area was very sensitive to hydrodynamic effects and prone to soil erosion and landslide. (3)The main erosion in this area included gully erosion, sheet erosion, debris collapse, and landslips. Expansive soil was especially prone to debris collapse and sheet erosion. ? For barren lands without vegetation cover and with very high soil erosion intensity, soil erosion could be under control after restoring vegetation. ?Splash erosions outside forests of Pinus Caribaea and Albizia kalkora were higher than those inside forests. |
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