不同气候带造林的气候调节效应及其机理研究

Warming or cooling effects of afforestation in variable latitude were depended on the balance between carbon sequestration and surface energy budget. Therefore, when only increased carbon sequestration of afforestation was considered, it may lead to an underestimation of the climatic benefits in tropical regions, but an overestimation in high-latitude boreal and temperate regions. Several researchers agree that afforestation in boreal zones could warm the earth, and cool in the tropics. However, the climate benefits of forestation in temperate and arid zones were argued without consistent understanding on its mechanisms, processes and threshold. To recognize the effects of afforestation on regional climate accurately and comprehensively, the Loess Plateau, Xilin Gol League, Poyang Lake Basin were selected as typical study area of temperate arid zone, temperate humid zone, subtropical zone. Integration of satellite - ground experimental means was applied that consists of terrestrial comparative observations, remote sensing collaborative inversion, ecological model simulation, climate modeling, and GIS analysis. The goal is to study the impact mechanisms of forestation on surface carbon budget and the radiation energy balance and to determine the contribution rate of forestation on climate warming through changes in greenhouse gas balance and land - atmosphere interface process. Thus quantitatively analyze and assess the climate regulation effect of forestation in different climate zones. The study aims to improve and deepen the scientific understanding of the causes of climate change, and to provide a scientific basis for regulating forestation activities, and developing strategies to address climate change and ecological and environmental protection.

造林在不同气候带的增温/降温效应取决于地表碳调节和能量收支，仅考虑碳蓄积会导致造林的气候调节效应在热带的低估和寒带的高估。“寒带造林增温、热带造林降温”获得一致认识，而温带和干旱区造林对气候影响的争论较大，其作用机理、过程模式和临界阈值等问题尚未充分了解。为了准确、全面地认识我国造林对区域气候的影响，本项目选择我国黄土高原、锡林郭勒盟、鄱阳湖流域分别作为温带干旱区、温带半干旱区、亚热带湿润区的典型造林区，采用地面碳水热对比观测、遥感协同反演、生态模型模拟、气候模式模拟、GIS综合分析等星-地一体化手段，研究典型区造林对地表碳收支与辐射能量平衡的影响机理，厘定造林导致温室气体收支变化与陆—气界面过程变化对气候变暖的贡献率，进而定量评估不同气候区造林的气候调节效应，完善和深化对气候变化成因的科学认识，为国家调控造林活动、制定应对气候变化和生态保护相关策略提供科学依据。

本项目以造林的气候调节效应为研究主线，选择我国黄土高原、锡林郭勒盟、鄱阳湖流域分别作为温带干旱区、温带半干旱区、亚热带湿润区的典型造林区，在收集、整理与整合现有研究资源和成果的基础上，采用地面对比观测、遥感协同反演、生态模型模拟、气候模式模拟、GIS综合分析等实验手段，开展造林对生态系统碳收支、能量收支等气候调节功能的影响，阐明造林引发温室气体收支变化和改变地表陆-气界面过程的机理，进而定量模拟和评估我国大规模造林活动的气候调节效应。. 主要研究内容包括：造林对气温影响差异的国别对比；退耕还林等土地利用变化对地表反照率的影响机理；不同纬度造林对区域气温影响的数值模拟；亚热带湿润区造林对生态系统碳收支的影响机理；过去和未来20年我国不同区域森林等主要陆地生态系统碳固定量；不同气候带造林对区域温度影响的生物物理效应；不同气候带退耕还林的气温调节效应差异；基于生物物理效应和生物化学效应的造林气候调节值估算；未来不同经济社会发展与气候变化情景下造林的碳效益模拟。. 重要结果：造林对区域温度的影响具有纬度地带性，总体趋势是随着纬度的升高，造林后降温作用减弱、增温作用加强。造林对温度影响的生物物理效应与区域气候背景极为相关，干旱半干旱地区造林引起的净辐射增加程度大于潜热通量的增加程度，因此地表对大气供热表现为增温效应；亚热带湿润区造林引起净辐射减少及潜热通量增加，在青藏高原、中温带湿润区的净辐射增加程度小于潜热通量的增加程度，因此地表对大气供热皆表现为致冷效应。仅考虑碳调节，我国各气候区造林皆表现为碳蓄积过程，具有碳汇作用即致冷效应；同时考虑碳调节和地表能量收支，我国亚热带造林的致冷效应是仅考虑碳调节致冷效应的1.25-1.45倍，而干旱半干旱区的致冷效应则为仅考虑碳调节效应的约一半。. 本研究的科学意义在于完善和深化对气候变化成因的科学认识，为国家调控造林活动、制定应对气候变化和生态保护相关策略提供科学依据。