黄土高原植被净初级生产力时空变化特征及驱动因子分析

Spatial and temporal variation and driving forces for the net primary productivity of vegetation on the Loess Plateau

【目的】探究黄土高原地区植被净初级生产力(NPP)多年时空演变规律以及同期人类活动及自然因子对其产生的复合影响,为当地生态修复规划和实施提供参考。【方法】利用CASA模型计算并分析2001-2019年黄土高原地区植被净初级生产力及其时空分布格局,并基于地理探测器对植被NPP进行驱动因子和机制分析。【结果】(1)2001-2019年黄土高原地区植被NPP整体呈显著上升趋势,年均增加速率为5.59 g/(m2·a),显著增加的区域主要分布在黄土高原中部沟壑区以及丘陵沟壑区。基于重心模型对NPP在空间上重心的分析结果表明:黄土高原NPP重心迁移呈现出阶段性变化特征,平均NPP重心点南部的NPP增量与增速在多数年间均高于北部。不同土地利用类型中,林地的NPP均值最高。由于土地利用转移主要在耕地与草地之间相互转化,占总变化面积的75%,因此,耕地与草地NPP均值变化的线性趋势率最高。(2)地理探测器结果显示年降水量与干燥度指数是影响黄土高原地区植被NPP的主导自然因素,随后依次为土地利用类型、年均气温、坡度等。交互探测器结果表明各因子交互作用均呈现增强趋势,且对植被NPP无显著影响的因子通过与其他因子发生交互作用的方式对NPP产生显著影响。风险探测器识别的适宜植被生长的范围在不同土地利用类型中存在差异,多数地类NPP的年降水量适宜区间在500~1000 mm之间。除未利用土地外,其他地类的NPP适宜温度区间在10~14℃之间。耕地NPP的适宜海拔高度区间在19.62~548.43 m之间,而其他地类在1000~2500 m之间。林地NPP的坡度适宜范围相对较大,不同地类最适宜的坡向不相同。【结论】黄土高原2001-2019年间植被恢复工程对生态系统NPP贡献显著,环境因子间的交互作用会增强单因子对植被NPP的影响,不同环境因子的NPP适宜累积区间在不同土地利用类型下存在差异,本研究结果为该地区实际植被恢复与管理工作提供了理论依据。

[Objective]This paper aims to explore the spatial and temporal evolution of net primary productivity(NPP)of vegetation in the Loess Plateau over many years and the combined impact of human activities and natural factors in the same period on it,so as to provide reference for the local ecological restoration planning and implementation.[Method]CASA model was used to calculate and analyze the NPP and its spatial and temporal distribution pattern of vegetation in the Loess Plateau from 2001 to 2019,and the driving factors and mechanisms of vegetation NPP were analyzed based on Geodetector.[Result](1)The vegetation NPP in the Loess Plateau showed an overall significant increasing trend from 2001 to 2019,with an average annual increase rate of 5.59 g/(m2·year).The areas with significant increase in NPP were mainly distributed in the central gully and hilly gully areas of the Loess Plateau.The analysis of the spatial center of gravity of NPP based on the center of gravity model showed that the migration of NPP center of gravity in the Loess Plateau exhibited a periodic change feature,with the average NPP increment and growth rate in the southern part of the center of gravity being higher than in the northern part for most years.The significant NPP increased was detected mainly in the central gully area and hilly gully area of the Loess Plateau.Among different land use types,forest land had the highest mean NPP.Land use transfer was mainly transformed between cultivated land and grassland,accounting for 75%of the total change area,leading to the highest rate of linear changes in NPP.(2)The results of geographic detectors showed that annual precipitation and dryness index were the dominant natural factors affecting vegetation NPP in the Loess Plateau,followed by land use type,annual average temperature and slope.The results of the interaction detector showed that the interaction of factors was mainly bi-factor enhancement or nonlinear enhancement,and the factors that had no significant impact on vegetation NPP had a significant impact on NPP when interacting with other factors.The optimal range of vegetation NPP identified by the risk detector varied among different land use types.The optimum annual precipitation range for NPP of most land use types was 500−1000 mm.Except for unused land,the suitable temperature range for NPP of other land use types was between 10 and 14℃.The suitable altitude ranged for NPP of cultivated land and other land use types were 19.62−548.43 m and 1000−2500 m,respectively.The suitable slope range for NPP of the woodland was relatively spanned,and the suitable slope aspects varied among different land types.[Conclusion]The results of this study show that vegetation restoration on the Loess Plateau from 2001 to 2019 contributes significantly to ecosystem NPP.The interactions between environmental factors enhance the influence of single factors on vegetation NPP.Moreover,the optimal accumulation ranges of NPP of different environmental factors are different for varied land use types.Our study provides a theoretical basis for the vegetation restoration and management practices in this area.