人工林种植和生长对黄土高原生态系统固碳和水文调节功能的影响——基于遥感时序分析证据

Impacts of plantation and its growth on carbon sequestration and hydrological regulation functions on the Loess Plateau based on remote sensing time series analysis

随着生态恢复工程的进展,黄土高原人工林种植面积不断增加,黄土高原人工林生态系统服务功能的响应变化仍存在争议。基于黄土高原人工林的时空分布和种植年份信息,从生态系统净初级生产力(NPP)、蒸散发(ET)以及土壤含水率(SMC)三个维度评估黄土高原地区人工林生态系统固碳和水文调节服务功能的动态变化及其对天然林和整个区域生态系统功能的影响,并进一步研究2000—2020年间人工林林龄对生态系统服务功能的影响。天然林的NPP相对于整个区域的百分比基本保持不变,维持在21%左右;而人工林的NPP相对于整个区域的百分比显著增加,并在2009年超过了天然林,成为黄土高原NPP增加的主要来源。人工林占整个区域的ET百分比和SMC百分比均显著增加,分别由不到2%增长至13.9%、1.5%上升至11.8%。至2015年,黄土高原人工林的ET和SMC已经逐步趋于稳定。随着林龄增大,SMC变化速率和变化量不断下降。ET与林龄成正相关,而SMC与林龄负相关,表明具有不同年龄结构的人工林将有效减弱树木生长所引起的土壤干旱的影响。尽管黄土高原人工林林龄与NPP、ET和SMC变化速率和变化量之间存在显著相关性(P<0.01),但由于现阶段此地区人工林多为幼龄林和中龄林,未来这种显著相关关系是否持续有待进一步研究。

With the progress of ecological restoration projects,the area of planted forests on the Loess Plateau is continuously increasing,but the response of planted forest ecosystem service function is still controversial.Based on the spatio⁃temporal distribution and planting year of planted forests on the Loess Plateau,this study assessed the dynamic changes in carbon sequestration and hydrological regulation service functions of planted forest ecosystems from three dimensions:net primary productivity(NPP),evapotranspiration(ET),and soil moisture content(SMC),examined the impacts of planted forests on natural forests and the overall regional ecosystem functions,and furthermore,investigated the influence of planted forest age on ecosystem service functions from 2000 to 2020.The proportion of NPP from natural forests relative to the entire region remained relatively constant,at around 21%.In contrast,the contribution of NPP from planted forests had shown a significant increase,surpassing that of natural forests in 2009 to become the primary driver of NPP growth on the Loess Plateau.The share of planted forests in the region′s ET and SMC had also seen a notable rise,increasing from under 2%to 13.9%and from 1.5%to 11.8%,respectively.By 2015,the ET and SMC of planted forests on the Loess Plateau had gradually stabilized.As the age of the forest increased,the rates and quantities of SMC changes decreased.The positive correlation between ET and forest age and the negative correlation between SMC and forest age indicated that establishing planted forests of different age classes would effectively mitigate the impact of tree growth on the reduced soil moisture.While a significant correlation existed between the age of planted forests and the rate and magnitude of NPP,ET,and SMC changes(P<0.01),the persistence of this relationship in the future,given the current predominance of young and middle⁃aged planted forests in the region,requires further investigation.