兴安落叶松林火干扰后土壤有机碳含量变化

在大兴安岭兴安落叶松林区,选择不同恢复年限各种火烧强度(重度、中度、轻度)的火烧迹地进行调查并采集土壤样品,对火后有机层和矿质层有机碳含量变化进行研究,以期为进一步开展森林火灾对区域碳平衡影响的定量评估提供科学依据。研究结果表明:火干扰对土壤有机碳含量变化的影响包括火烧即时影响和火后生境条件变化带来的间接影响。火干扰样地有机层的积累与转化主要是通过火后林冠郁闭度的变化影响的,其有机碳总储量低于对照样地。对于矿质层土壤,重度和中度火干扰后,如果样地发生植被序列演替,即阔叶林植被入侵,样地郁闭度增加迅速,凋落物积累量增大,土壤有机碳含量将随着过火年限的增加而增加;如果样地发生自我更新,样地郁闭度增加缓慢,凋落物分解量大于积累量,土壤有机碳含量将会在一定时间内随着过火年限的增加而减少;但是,无论样地发生植被序列演替还是自我更新,土壤有机碳含量短时间内均无法恢复到火前水平。轻度火干扰后,土壤有机碳含量短期内先增加,随着植被更新情况的发展最终趋于平衡。

The variability of soil organic carbon content in Larix gmelinii forests after fire disturbances

Fire is the primary disturbance agent in boreal forests, and exerts a major influence on the carbon cycle in this ecosystem. Fire disturbances not only alter the composition of species in the local forest ecosystem and the structure, functions and development of forests across landscapes, but also result in remarkable variations of soil physical and chemical properties, the relative content of nutrient elements and the storage of soil organic carbon. Using remotely sensed data from a Larix gmelinii forest before and after fire in the Great Xing''an Mountains, we calculated the Composite burn index (CBI), combined with interviews with local guides and field investigations to estimate the intensity and disturbance range of the fire. Soil surveys, sample collections and analyses of different areas of restoration after fire disturbances of different intensities (high, intermediate and low intensity) were performed. We researched the soil organic carbon variables in detail and discussed the impact of organic and mineral horizons of different fire intensities on soil organic carbon, in order to provide a scientific basis for the quantitative evaluation of the regional carbon balance after forest fires. The results showed that the effects of fire on soil organic carbon included the immediate effects of fire and the indirect effects of changes in habitat conditions after fire. The organic layer was partially or completely burned off during fire disturbances. Moreover, fire changed the morphological characteristics of mineral horizons, increased bulk density and reduced the organic carbon content. The accumulation and transformation of organic carbon was mainly influenced through the consequent changes in plant species, canopy density and recovery times after fire. The total organic carbon content of the organic layer of the fire disturbance sample plot was lower than that of the control. The organic horizons were markedly altered by fire. The organic carbon content in the organic horizons varied along with the extended recovery time, but no area recovered to the same level as the control within a short time period. Effects of fire disturbance on soil color were not evident, but fire disturbance destroyed the soil structure, decreased soil porosity and increased bulk density in a manner that was positively correlated with increasing fire disturbance intensity. The soil organic carbon content increased along with the extended recovery time if relay succession occurred in the sample area after a high or intermediate intensity fire. This resulted from the growth of invasive broad-leaved forest vegetation, a denser canopy and larger amounts of accumulated litter. However, if self-replacement took place in the sample area, then the canopy density was reduced and the soil organic carbon content decreased with increasing ages of fire over time. Nevertheless, regardless of the relay succession or self-replacement that occurred in the sample area, no area recovered to the same level as the control within a short period of time. The soil organic carbon content increased in the short term after low intensity fire disturbances with the regeneration of vegetation. It eventually returned to the baseline with ongoing changing conditions within the area.