茂兰退化喀斯特森林植被自然恢复中生态系统碳吸存特征

Characteristics of carbon sequestration during natural restoration of Maolan karst forest ecosystems

为了了解退化喀斯特森林自然恢复中生态系统碳吸存趋势,采用空间代替时间的方法,研究了茂兰退化喀斯特森林自然恢复中生态系统碳吸存特征。结果表明:总体上植被生物量随恢复进程递增,其中乔木层与其变化一致,草本层、灌木层则相反;喀斯特植被的地上与地下生物量之比较低,尤其灌木层的地上与地下生物量之比最低;加权平均含碳率随恢复进展递增;随恢复进程,植被乔木层碳密度递增,草本层、灌木层碳密度递减;总体上生态系统及其植被、土壤的碳密度由恢复早期(草本阶段、草灌阶段)经中期(灌木阶段、灌乔阶段)至后期(乔木阶段、顶极阶段)呈增加趋势,而凋落物的相反。在贵州茂兰国家级自然保护区喀斯特森林的恢复进程中,植被对生态系统碳库的影响最大,尤其是木本植被,而土壤的影响较小,因此,加强植被恢复对喀斯特地区生态系统碳汇具有极重要的意义。

Aims The objective of this study was to characterize the ecosystem carbon sequestration during natural restoration process of karst forest vegetation.Methods We adopted the ＂space for time＂ approach to examine the pattern of carbon sequestration in karst forest ecosystems along the natural restoration process.Forest vegetation types representing six typical successional stages were selected and investigated,which include herb stage,herb to shrub stage,shrub stage,shrub to arbor stage,arbor stage,and climax stage.Twenty-four plots of 30 m × 30 m were established on sites of the six forest types,and samples of plants,litter and soil were collected in each plot.Important findings The total vegetation biomass increased from 7.97 to 166.83 t·hm^–2 with advancement of restoration stages,corresponding to the trend of changes in biomass for the arbor layer（from 41.77 to 164.59 t·hm^–2）,but with declining biomass for the herb layer（from 8.45 t·hm^–2 at the herb to shrub stage to 0.68 t·hm^–2 at the climax stage） and the shrub layer（from 32.87 t·hm^–2 at the shrub stage to 1.56 t·hm^–2 at the climax stage）.The ratio of above ground to belowground biomass in karst vegetation was relatively low（varying between 1.26 and 2.03）,especially for the shrub layer（varying between 1.23 and 1.45）.The weighted average carbon content increased from 36.76% to 48.74% with the process of restoration.In the process of the natural restoration,the carbon density in the arbor layer increased from 19.44 to 80.40 t·hm^–2,but decreased from 3.19 t·hm^–2 at the herb to shrub stage to 0.23 t·hm^–2 at the climax stage in the herb layer and from 15.13 t·hm^–2 at the shrub stage to 0.69 t·hm^–2 at the climax stage in the shrub layer.The overall carbon density showed an increasing trend from the early stages（herb and herb to shrub stages）,through the middle stages（shrub and shrub to arbor stages）,to the latestages（arbor and climax stages） at levels of ecosystems（from 15.72 to 99.37 t·hm^–2）,vegetation（from 2.93 to 81.31 t·hm^–2）,and soil（from 8.26 to 18.80 t·hm^–2）,accompanied by a reduction in litter（from 4.97 to 1.53 t·hm^–2）.It can be concluded that vegetation,especially the component of woody plants,has the greatest influence on ecosystem carbon stocks during the recovery progress of karst forests,with little effects of soils.Therefore,it is important to facilitate the recovery of vegetation for enhancing karst ecosystem carbon sink.