Study On Growth Processes And Ability Of Carbon Sequestration Of Qinghai Spruce Forest In Qilian Mountains

Against the background of global warming, forest has been seen as a carbon sink for decreasing the CO2 concentration in atmosphere, because of its function of carbon fixation and oxygen release. In particular, temperate forests that cover only 8% of the global land surface were estimated to be responsible for around 40% of total terrestrial C uptake. However, the temperate forest, located in the Qilian Mountains of northwest China, has suffered or are suffering from deforestation. The function of carbon fixation and oxygen release has been affected by the deforestation in this region. If there have more reasonable conservation and restoration strategies for destroyed forest, the forest will fix more carbon, and these strategies have important real-world implication for decreasing the CO2 concentration in atmosphere and retarding global warming. This study selected the Qinghai spruce fortes (Picea crassifolia) as the research object, which is the dominant species in the Qilian Mountains of northwest China. We studied the growth processes and habitat suitability model (HSM) of Qinghai spruce, obtained the areas for its prior restoration and conservation, and roundly evaluated its ability of carbon sequestration. We hope the study about its growth processes can provide some references for studying its eco-hydrological process in this region, and also hope the approach of this study could be a useful way of helping decision-makers in other regions of the world draft effective restoration/conservation plans and study the ability of carbon sequestration for deforested lands.The study can be divided roughly with two subjects:(1) we studied the growth processes (stem volume and biomass of Qinghai spruce) based on process and empirical models, in which for running the process model we also improved a mountain microclimate simulation model to provide daily meteorological data; (2) we studied the HSM of Qinghai spruce and predicted its habitat suitability and potential distribution, and based on the first subject we then calculated the potential carbon store and evaluated its ability of carbon sequestration under different habitat suitability. Based on above subjects, this study has the conclusions as follows:1. In terms of improving the mountain microclimate simulation model (MTCLIM):(1) Many factors influence air temperature and precipitation. Topographical attribution and wind direction are crucial factors in mountainous areas. The introduction of wind direction and topographical attribution to the MTCLIM model has significantly improved the performance of the MTCLIM to predict daily temperature, daily precipitation, and daily relative humidity.(2) MTCLIM is not suitable for use in a large mountainous area with few stations. In addition, it is difficult to derive surfaces of meteorological data. The modified MTCLIM can make up for these disadvantages.(3) The modified MTCLIM was applied to map meteorological data on a daily-time-step. The distributed temperature and precipitation were validated by short meteorological records of 24 weather stations. We found RMSE and MAE were lower than previous results, therefore, our results could be used as inputs for distributed hydrological and ecological models in the study area.2. In terms of growth processes of Qinghai spruce forest:(1) The stem volume of Qinghai spruce can be explained by the mechanism processes of BIOME-BGC. However, the BIOME-BGC needs numerous parameters for running, besides, the accuracy of meteorological data can affect the modeling accuracy. The study did not consider the thinning process of tree when we used the BIOME-BGC, and we just studied the growth processes of Qinghai spruce with a fixed tree density.(2) Based on this study, it can be concluded that BIOME-BGC is able to well estimate the stem volume of individual Qinghai spruce by introducing the crown projection area (CPA). Moreover, the introduction of CPA can reduce the overestimation of stem volume for relatively younger stands and underestimation for relatively older stands in BIOME-BGC. Therefore, CPA is a critical parameter that influences stem volume simulated by BIOME-BGC at individual and stand levels. Although the correction may be not suitable for the mature forest stand, this correction is important for modeling early forest growth. So, we conclude that CPA is an important factor that should be considered in BIOME-BGC.(3) In the stand of Qinghai spruce forest, the biomass is the function of stem volume and tree density, by which the biomass at stand level can be calculated by the stem volume at individual level. Biomass of Qinghai spruce presents a trend of increase first and then decrease with stand age increasing, and when stand age was about 183 years the biomass will be highest. In addition, Biomass of Qinghai spruce presents a certain zonality in the geographic space, which is affected by the different hydrothermal conditions. In a hyper-volume space, different combinations of environmental variables will result in different growth status of Qinghai spruce, and affect the carbon fixation.3. In terms of habitat suitability of Qinghai spruce forest:(1) Habitat suitability and potential distribution of Qinghai spruce forests in the study area can satisfactorily be predicted with the HSM based on average annual precipitation (P), average air temperature in July (T), and solar radiation (R). The optimal combination of T, P, and R is 11.5℃,380 mm, and 2×103 kWh/m2, respectively, to produce the optimal niche for the growth of Qinghai spruce.(2) A comparison between the actual distribution area and an area with higher suitability (habitat suitability value ranges from 0.627 to 1) suggests that restoring Qinghai spruce has great potential. The prior restoration and conservation areas are 43 km2 and 56.65 km2 in the study area, respectively. In these areas, restoring and conserving Qinghai spruce forests will allow more carbon sequestration.(3) Against the background of global warming, the conservation and restoration of destroyed forests around the globe are crucial for C sequestration. The approach of this study could be a useful way for helping decision-makers in other regions of the world draft effective restoration/conservation plans for deforested lands. The implementation of these plans will reduce CO2 concentration in the atmosphere and, in turn, retard global warming.4. In terms of carbon sequestration ability of Qinghai spruce forest:(1) the carbon per unit of Qinghai spruce in the restoration area ranges from 179 to 182 t/hm2 when stand age in biomass function is set 183 years, and the carbon has a small difference in the geographical space, which is resulted from small hydrothermal difference probably. In addition, averaged carbon per unit is 180 t/hm2, and total potential carbon in the restoration area is 7.3×106 t. These results indicate Qinghai spruce has the strong ability of carbon fixation.(2) The carbon fixation of Qinghai spruce forests are different under different habitat suitability in the geographical space, and under the higher habitat suitability they can store more carbon.(3) The water use efficiency of Qinghai spruce forests was estimated by BIOME-BGC under different habitat suitability, and we found under the higher habitat suitability Qinghai spruce forest can use relatively lesser water to fix relativity more carbon.(4) There are huge potential carbon in the Qinghai spruce, more reasonable ways for restoration and conservation can make Qinghai spruce fix more carbon. In practice, the work can be carry out based prior restoration and conservation areas.