Research On Arborous Layer Aboveground Biomass And Gross Productivity Of The Typical Forest Types On The Southern Slope Of Qinling Mountains

The forest ecosystem contains85-90%of carbon storage of terrestrial ecosystems, and plays an important role in responding to global climate change caused by CO2emission. With the decrease of forest area and increase of greenhouse gases like CO2, it’s more and more important to estimate forest biomass and carbon storage. Qinling forest area, as one of the biggest forest carbon storage areas, plays an important role in balancing regional carbon. However, very few studies are about biomass in this area. This study used the data from field survey and allometric models established by other experts, aiming to begin with forest structure, arborous layer biomass, gross primary productivity (GPP) and interference factors, to explore the biomass variation in the south slope secondary forest in its primary stage of natural succession, which can provide references for the planning of operation and sustainable forest management. The main results of this research were summarized as follows:(1) The main secondary mixed forest types of the study region includes Pinus tabulaeformis and Quercus mixed forest, Pinus armandi and Quercus mixed forest, Larix and Quercus mixed forest and some broadleaved mixed forest. The mean forest age of this area ranges from34to41years, while, the diameter structure concentrate in the small classes, that was,5<DBH<20cm. Through comparing the stem density of the main three forest types, it shows that, Pinus tabulaeformis and Quercus mixed forest> Pinus armandi and Quercus mixed forest> Larix and Quercus mixed forest. A great number of stems with small diameter in the Pinus tabulaeformis and Quercus mixed forest reflect the disturbance from humanity, but the diversity of understory vegetation demonstrate the well-developed condition of the stand. However, more signs of planting and logging were found in the Pinus armandi and Quercus mixed forest. Also, there are plenty of small diameter stems in the Larix and Quercus mixed forest originating from planting, which cause the forest age same as the small ones.(2) The variation tendency of aboveground biomass of Pinus tabulaeformis and Quercus mixed forest, Pinus armandi and Quercus mixed forest, Larix and Quercus mixed forest all monotonically increase as the letter "J", with the relationship of, Pinus tabulaeformis and Quercus mixed forest> Pinus armandi and Quercus mixed forest> Larix and Quercus mixed forest. Nevertheless, the curve of GPP shows as "S", but not very obvious. The relationship of these three forest types shows the same trend as biomass when the forest age less than45years. After that, the GPP of Pinus tabulaeformis and Quercus mixed forest still greater than the other two, while Larix and Quercus mixed forest will exceed Pinus armandi and Quercus mixed forest.(3) With the increase of altitude, both forest biomass and productivity decrease. The average individual biomass of broadleaved species keeps falling, while that of conifers increase. Simultaneously, the biomass proportion of conifers also has a growing trend. When altitudes over than1100m or even higher, per unit area and individual productivity of conifers is higher in coniferous species than that in broadleaves. Consequently, conifers are better adapted to habitat changes caused by altitudinal increase.(4) With increase in altitude, stem density and basal area per unit area both show a decrease tendency. Forest with high density usually has a relative small mean diameter, which not useful for the increase of biomass and always with low biomass and individual productivity. Usually, older individuals hold bigger biomass. However, the older forests sometimes cause relative lower forest productivity, to some extent, hinder the healthy development of forests.(5) Except for some steep area of high altitude, the plant of the research area was destroyed to different degrees by humanity. Overall, the aboveground biomass negatively related to disturbance (r=-0.707, P<0.01), which means the biomass tend to decrease with the increase of disturbance. The disturbance at low altitude mainly includes human action, nature disaster and so on. While, that at high altitude majorly contains planting and intermediate cuttings. In general, the disturbance intensity gradually decreases with the rising altitude.The results showed that the forest biomass estimating in regional scale is different from that for larger scales. We must take into consideration inference factors and environment changes. This research obtains some conclusions and suggestions with guidance significance for regional scale sustainable forest management.