Distributon Character Of Alpine Shrubs Biomass Along An Elevation Gradient In Qilian Mountains

Qilian Mountains, which sites in the north-east line of the Tibet Plateau, is themajor ecological barrier of the Hexi Corridor and the provinces and regions in thedownstream, and its ecosystem is complex and fragile. Qilian Mountains stretchedinto the northwest arid area, is not only the “Green Reservoir” for the economy of theHexi Corridor and provinces and regions in the downstream, but also for thesustainable development of the society. Meanwhile it takes significant part in thestabilizing the situation of the national development because: it is the safeguard forthe ecology security of the oasis in Hexi Corridor, which is about60.4%of the Gansuprovince area. As the biotic climax, the water resources conservation forests of QilianMountains in the northwest arid area has had went through the rigorous naturalselection, it acts on the precipitation, water resources conservation, soil conservationand climate improvement stably. Under the background of global climate change, theaccelerating melting glaciers will influence the global climate, threaten the security ofthe human living condition and it may change the ecotope and habit of muchpropagation. The alpine shrubs of Qilian Mountains, which sits beyond the tree line ofthe Picea crassifolia forest, is the most effective forest type, therefore, to study thebiomass of the alpine shrubs in Qilian Mountains is the main reflection of theproductivity of the ecosystem, the main measure of the structure and function of thecommunity. And because the biomass of the shrubs impacted by the elevation gradientand environmental factors, including the limitation of the field investigation in thehigh altitude, the response process made by shrub biomass on the elevation gradient isnot clear. So, this study took the alpine shrubs in the3300³700m of the PailugouCatchment of Qilian Mountains as the object, the plot, subplot harvesting method andmining trenches method had been used to observe the total biomass and organicbiomass of the shrubs in various elevation gradients and also to analyze therelationship between the distribution character of the shrubs biomass andenvironmental factors. The aim of this passage is to provide important theoreticalbasis and data for the protection of ecological environment of watershed and theresponse for alpine shrub on global climate change. The chief conclusions showed asfellows:1) The biomass of the shrubs of the community and its organic biomass all reduced with the increase of the elevation, the alpine shrubs biomass and the altitude hadshowed a significant negative correlation （P<0.01, R²=0.889）. And in the3300³500m, the variation of the shrubs biomass was not obvious. But beyond the3500m, the biomass reduced significantly, the variation reached about2⁶times. Thetotal biomass of each altitude from the big to the small were:3300m>3400m>3500m>3700m>3800m. The ratio between the underground part andthe aboveground presented an obvious variation （P<0.05）, the ratio of root biomassand stem biomass increased firstly and then reduced as the elevation increasing. Theroot-stem ratio and the altitude showed an obvious polynomial relationship（R²=0.710）.The root-stem ratio reached the biggest in3500m, was1.93, and in the3300m the root-stem ratio reached the smallest, was0.82.2) The total biomass of the herbs of the community presented a fluctuation changeas the increasing of the elevation, and in the3400m the total biomass of the herbsreached the biggest (1213.07kg·hm^-2), and in the3700m it reached the smallest(358.90kg·hm^-2). The spatial variation of the herbs biomass was not obvious. Theaboveground biomass of the herbs presented a singlet with the increasing of theelevation, and in the3400m the aboveground part reached the biggest(263.91kg·hm^-2).And the underground biomass of the herbs increased firstly and then reduced with theincreasing of the elevation, the tuning point was3400m. In each elevation, theroot-stem ratio of the herbs changed significantly, and in3300m and3700m the ratiowere bigger.3) The biomass of the litters in the shrub community showed an singlet style as thechanging of the elevation, and in the3400m it reached the biggest, and in3300m thebiomass of the litters was the smallest. The thickness of the litters and the elevationalso showed an obvious correlation. In the test area, the litters’ biomass of the3600mpresented the most significant variation.4) The total biomass of the shrubs community appeared a singlet style with theincreasing of the elevation. The herbs changed only little, and the ratios of the littersand the shrubs displayed an fluctuation change, and the change was similar, they were56.24%，57.20%separately. The litters biomass was bigger than the shrubs expect in3300m. And the aboveground biomass and underground biomass of the herbs bothwere small, the herbs biomass was about2%of the shrubs community5) The synthetic change of the environmental factors in the elevation gradient took an obvious effect in the shrubs biomass and its organic biomass, the soil water content,soil bulk density presented much more significant than the soil temperature. Thecorrelation coefficients between the soil water content and the shrubs communitybiomass, shrubs biomass, herbs biomass and the litters biomass were:0.105、0.649、0.339、0.867separately. With the increasing of the soil bulk density, the shrubsbiomass of the community reduced （R²=0.940）, the herbs displayed an inverse “U”shape （R²=0.993）, the litters biomass presented an fluctuation style（R²=0.862）, andthe biomass of the community also showed an inverse “U” shape（R²=0.583）.The soiltemperature changing range was6.35⁸.88℃in the test area. The total biomass of theshrubs community reached biggest when the soil temperature was about7.3℃, andunder other soil temperature, it showed unobvious change. With the changing of thesoil temperature, the shrubs biomass displayed an inverse “U” shape, the herbsbiomass and the litters biomass all presented the fluctuation change.