新疆草地长时序地上生物量时空演变及其驱动力

Spatiotemporal evolution and driving forces of long-term aboveground biomass in grasslands of Xinjiang

【目的】草地是陆地生态系统的重要组成部分,草地地上生物量可以直接反映草地资源的现状。准确评估草地地上生物量并揭示其长期变化趋势是草地生产力维持与提升、草地合理载畜量核定以及草地可持续利用的基础。【方法】本文依据中国草原分区,使用多年累积采集的11703个野外地面调查样方数据,对新疆维吾尔自治区的7个草原亚区分别构建草地地上生物量随机森林回归模型和多元逐步线性回归模型,通过精度评估确定最佳模型;然后使用Landsat影像反演得到30 m分辨率的1990—2020年新疆草地地上生物量,在揭示31年地上生物量时空演变的基础上,从气象、地形、土壤和人类活动4个方面选择了14个可能的驱动因子,使用地理探测器分析其主要驱动力。【结果】①7个草原亚区的草地地上生物量随机森林回归模型平均R2达到了0.74,平均RMSE为786.89 kg/hm^(2),均优于多元逐步线性回归模型。②1990—2020年新疆草地地上生物量整体呈现增加趋势,全疆草地31年平均地上生物量为2137.31 kg/hm^(2);其中,山地草甸类的平均地上生物量最高(4847.47 kg/hm^(2)),高寒荒漠类的平均地上生物量最低(804.51 kg/hm^(2))。新疆草地地上生物量年平均变化值为15.05 kg/hm^(2)/a。③新疆草地地上生物量空间格局呈现山区多于平原,北疆多于南疆的分布特点;伊犁河流域和阿勒泰地区草地地上生物量较高,准噶尔盆地以及塔里木盆地东南部草地地上生物量较低。④地理探测结果显示,3个时间段的降水和土壤有机碳含量对新疆草地地上生物量有着显著的影响;值得注意的是,人类足迹的影响在2010—2020年这一时间段有所增强。【结论】1990—2020年新疆草地地上生物量保持持续增长的趋势,气象因素和土壤因素共同驱动着草地地上生物量的变化。未来需更加关注人类活动因素对草地地上生物量的影响,以实现新疆草地地上生物量持续向好发展。

[Objective]Grassland is an essential component of terrestrial ecosystems,and the aboveground biomass(AGB)of grassland can directly reflect the current status of grassland resources.Accurately assessing the aboveground biomass of grassland and revealing its long-term change trends are fundamental to maintaining and enhancing grassland productivity,determining reasonable livestock carrying capacities,and ensuring sustainable grassland utilization.[Methods]Based on the grassland zoning in China,this study used 11703 records of accumulated field survey quadrat data to establish random forest regression models and multiple stepwise linear regression models for aboveground biomass in seven grassland zones of the Xinjiang Uygur Autonomous Region.The optimal model was determined through accuracy assessment.Subsequently,Landsat imageries were employed to invert the results of 30 m resolution grassland aboveground biomass in Xinjiang from 1990 to 2020.After revealing the spatiotemporal change of grassland aboveground biomass over 31 years,14 potential driving factors were selected from four aspects:meteorology,terrain,soil,and human activities.Geographical detector was then used to analyze the primary driving factors,aiming to provide a scientific evidence for the future management,protection,and sustainable utilization of grassland resources.[Results]The main findings are as follows:(1)The average R²of the random forest regression models for the seven grassland zones was 0.74,with an average RMSE of 786.89 kg/hm^(2),outperforming the multiple stepwise linear regression models.(2)From 1990 to 2020,Xinjiang’s grassland AGB showed an overall increasing trend,with an average AGB of 2137.31 kg/hm^(2),and an annual average change of 15.05 kg/hm^(2)/a.(3)The spatial distribution pattern of AGB in Xinjiang indicated higher values in mountainous areas compared to plains and higher values in northern Xinjiang compared to southern Xinjiang.The Ili River Valley and Altay region had higher AGB,whereas the Junggar Basin and the southeastern Tarim Basin had lower AGB.(4)Geodetector analysis results for three time periods showed that precipitation and soil organic carbon content significantly influenced Xinjiang’s grassland AGB.Notably,the influence of the human footprint factor has intensified during the period from 2010 to 2020.[Conclusion]Xinjiang’s grassland AGB has shown a continuous growth trend from 1990 to 2020,driven by both meteorological and soil factors.In the future,greater attention should be given to the impact of human activities on AGB to ensure the sustainable development of Xinjiang’s grassland ecosystems.