The Impact Factors Of Growth And Regeneration Of Picea Crassifolia Growing At Timberline In The Qilian Mountains

Timberline, as the ecotone between alpine vegetations and subalpine vegetations ofmountains, is sensitive to the environment change and human disturbance. There is nouniversal theory of the timberline, although the hypothesis, such as energy(temperature)controling, environmental stress, growth limitation, reproductive disorder and carbonimbalance, could partially explain the dynamics of the timberlines in limited regions. Thenatural and man-made regeneration of Picea crassifolia at timeberline in the Qilian montainswas investigated in the dissertation to (a) understand the main impact factors of reproductivity,(b) reveal the influence of artificial regeneration on the moving of timberline,(c) study thechange trend of timberline under climate warming.The thesis mainly study the climate change in the past fifty years of Qilian montains, theseedling regeneration, growth of tree-ring and shoot of adult trees of Picea crassifolia in theXishui forest region, seeding and transplanting of seedling of Picea crassifolia over timberline,and analyses the influence elements of the growth and regeneration of Picea crassifolia. Themajor achievements of this study are summaried as follows:1. According to the analysis on temperature information of Xishui forest region, theannual average temperature increased significantly in the past fifty-two years, and the annualaverage precipitationis also increased slightly, where82%of rainfall in total year isconcentrated from May to Septermber. The atmospheric and soil temperature in differentelevations are above0℃from May or June to October and decreses0.44℃with the increasingof elevation in per100m. The temperature in warmest month in the timberline is13.60℃thatis higher than the globle mean temperature at timberline(10℃). The soil temperature in thetimberline is6.22℃that is similar with the globle soil temperature (6.7±0.80℃).2. The content of organic matters, total nitrogen, rapid available phosphorus and rapidavailable potassium decreased with the increase of soil depth, while the pH value increased with the increase of soil depth, and the total phosphorus contents didn't show significantvariation with different soil depth. The content of organic matters and total nitrogen decreasedwith the increase of elevation, while the content of total potassium and pH value decreasedwith the increase of elevation, and the content of rapid available phosphorus and potassiumdidn't show significant variation with different elevation.3. The growth limitation of Picea crassifolia varied from water to thermal with theincrease of elevation. The annual growth of Picea crassifolia at the lower elevation was biggerthan that in the higher elevation. Water was the limite factor for Picea crassifolia at the lowestelevation while thermal condition became the limite factor for it with the increase of elevation.The ending of growth time in the autum had great influence on the growth of Picea crassifolia.4. The growth of tree populations at the elevation of2900m and3000m was in stablestatus, which looks like the reverse "J"; the tree populations at the elevation of3100m began todecrease linearly; the tree at the elevation of3200m to3300m were vigorous with no died trees,and the tree populations at the elevation of3200m was waved, which indicated that thedevelopment of the Picea crassifolia population was in large change.5. The quantity of the regenerated seedlings decreased with the rising of elevation. In theregion lower than the elevation of3200m, the seedlings was of middle or low height (<25cm,25~55cm,>105cm). And the lower the elevation was, the more short seedlings there was. Theseedlings of the height between85and105cm was rare. In the region of the elevation of3300m, the quantity of seedlings of different height was similar, and the regeneration there wasnot good, where did not exsit seedlings of separate height.6. The regenerated seedlings varied from random distrbution to cluster by the rising ofelevation. At the elvation of2900m, the aggregation of the seedlings those height was below25cm distributed randomly, and the height of85~105cm distributed evenly; At the elvation of3000m, the aggregation of the seedlings of height in85~105cm and upper than105cmdistributed randomly; At the elvation of3100m,3200mm and3300mm, the aggregation of theseedlings showed cluster distrbution. The growth of seedlings those height was below25cmsignificantly correlated positively to the coefficient of the varation of rapid available potassium, coverage of dead litter, transmittance of arbor, the coverage of shrub, soil moisture content andthe total ground cover were bigger and negtively to the total potassium and the atmospherictemperature. The growth of seedlings of height in25cm～55cm and55～85cm positivelycorrelated to soil PH, atmospheric temperature and total potassium, and negatively to theorganic matters, coverage of ground vegetation and total ground coverage. The growth ofseedlings of height in85cm～105cm and upper than105cm positively correlated toatmospheric temperature, tree layer crown density and total potassium, and negatively to thesoil PH, soil moisture content and altitudinal gradients.7. The articicial seedling experiments of Picea crassifolia in forest line altitude fromelevation of3300to3500m showed that the seedlings could germinate but can't survival inwinter, and the higher the elevation was, the lower the germination ration was. Howere,five-years old transplanted Picea crassifolia seedling could survive from3300to3700m whichindicated that seed germination and seedling survival were important aspects that limited theupdation of timberline. The higher the elevation was, the slower the growth of the artificialregenerated seedlings was, the worse the growth was, and the higher the death rate was, whichindicated that the growth of the seedlings was significantly affected by elevation. The lowertemperature at high elevation might be the key factor that limited seed germination andseedling survival.8. The NSC content of leaves of Picea crassifolia exhibited a sustained increase by theincrease of the elevation. The growth was not affected by the carbon content as the risingelevation and decreasing temperature.Under the global warming, with the increase of temperature in the rigion of high elevation,the growth of Picea crassifolia speed up, the influence of lower temperature at timberline onthe seed germination and seedling survival of Picea crassifolia could be reduced, which wasgood for the expansion of timberline to the higher elevation.