Research On Biomass And Trace Elements Biological Cycle Of Urban Forests In Karst Areas

With the accelerated process of urbanization, the urban forests that could beautify and improve the urban ecological environment have become increasingly prominent. The concept of the city going into the forest-the forest embracing the city is more and more in-depth and the research work of urban forest carry out extensively.Guizhou located in the hinterland of China’s karst region of southwestern has uniqueness and fragility geological environment. Karst rocky desertification in Guizhou constrains the economy development and human life. Nutrient cycling based on forest vegetation, litter and soil and forest biomass is less, so the research of urban forest biomass and nutrient biological circulation of karst areas has important practical significance and guiding role.As the research object of typical Guiyang urban forest, the main content of this paper is the biomass and nutrient distribution and biological circulation characteristics of two urban forest(Betula luminifera and Italian poplar mixed forest,Sawtooth Oak forest), and the results showed that:(1) Tree layer biomass of Betula luminifera and Italian poplar mixed forest is4.03t·hm-2, the biomass of aboveground part has a proportion of84.86%and the underground part is15.14%。Tree layer biomass of Sawtooth Oak forest is129.04t·hm-2, the biomass of aboveground part has a proportion of76.77%and the underground part is23.23%。The proportion of the trunk with the tree bark in the two forests is59.36%、55.34%.(2) Biomass of Betula luminifera and Italian poplar mixed forest, Sawtooth Oak forest in different understory layers:shrub layer is6.052t·hm-2,1.993t·hm-2; herb layer is4.110t·hm-2、2.270t·hm-2; litterfall layer is2.510t·hm-2,5.138t·hm-2.(3) Biomass of Betula luminifera and Italian poplar mixed forest,Sawtooth Oak forest is16.70t·hm-2,136.44t·hm-2. In Betula luminifera and Italian poplar mixed forest(10years old), the tree layer biomass has a proportion of24.13%in total biomass and the proportion is93.21%in Sawtooth Oak forest(33years old).(4) Accumulation amount of trace elements in Betula luminifera and Italian poplar mixed forest soil is100.82t·hm-2, and amount of the Sawtooth Oak forest is101.25t·hm-2.(5) Accumulation amount of trace elements in tree layer is:Sawtooth Oak (589.6kg·hm-2)> Betula luminifera (12.88kg·hm-2)> Sawtooth Oak (5.32kg·hm-2). Annual net accumulation amount in tree layer is Sawtooth Oak (17.87kg·hm-2·a-1)> Betula luminifera (1.29kg·hm-2a-1)> Sawtooth Oak(0.53kg·hm-2·a-1).(6) The trace elements content of shrub layer is:Betula luminifera and Italian poplar mixed forest(477.01mg·kg-1)<Sawtooth Oak forest(628.33mg·kg-1), the herb layer is: Betula luminifera and Italian poplar mixed forest (371.39mg·kg-1)<Sawtooth Oak forest (458.04mg·kg-1). Accumulation amount of trace elements in shrub layer is Betula luminifera and Italian poplar mixed forest (28.82kg·hm-2)<Sawtooth Oak forest (8.46kg·hm-2), the herb layer is Betula luminifera and Italian poplar mixed forest (15.33kg·hm-2)> Sawtooth Oak forest (9.06kg·hm-2).(7) Retention of trace elements is:Sawtooth Oak forest (17.87kg·hm-2·a-1)> Betula luminifera and Italian poplar mixed forest (1.82kg·hm-2·a-1), return amount of trace elements is: Betula luminifera and Italian poplar mixed forest (0.622kg·hm-2·a-1)> Sawtooth Oak forest (1.943kg·hm-2·a-1). Absorption amount of trace elements in Betula luminifera and Italian poplar mixed forest is2.44kg·hm-2·a-1, and the amount is19.81kg·hm-2·a-1in Sawtooth Oak forest. Utilization coefficient of trace elements is:Betula luminifera and Italian poplar mixed forest(0.134)> Sawtooth Oak forest(0.034), the cycling coefficient is:Betula luminifera and Italian poplar mixed forest(0.254)> Sawtooth Oak forest(0.098).