Assessing impacts of climate change, extreme weather events and management regimes on biogeochemical and hydrological cycles in Canadian forest ecosystems

加拿大的森林生态系统约占该国表面积的40%或397 MHA，正受到气候变化和极端天气事件(如干旱、洪水和热浪)的严重影响。气候变暖在其中加速了水文循环，从而改变了生长、水平衡、干扰机制(昆虫、火)、土壤植物养分循环和相关的反馈(IPCC 2013,2018)。森林生态系统的组成、结构和功能的变化会影响区域气候，从而增加水资源和人类社区的脆弱性。迫切需要对森林生态系统的功能及其对气候变化和极端事件的反应有一个清楚的了解，以保持(或加强)它们封存大气二氧化碳和保护生态系统服务的能力。该提案将调查森林水文和养分循环的变化对三种不同年龄的针叶林和一种落叶林固碳潜力的影响，并探讨这些森林将如何应对未来的气候变化和极端天气事件。它将评估不同的森林管理措施(如可变保留采伐)将如何影响森林生长轨迹、能量交换、水文过程，以应对未来的气候压力和极端事件(如干旱、高温)。这项研究将利用地面数据集(如涡旋协方差、土壤二氧化碳排放、大气流量、生物测量学)和机载数据集(如无人机和卫星遥感)来探索不同年龄和物种的森林以及管理制度(间伐强度和空间模式)如何影响林分水分利用和生产力，以及对极端事件和环境变异性的反应。该提案还将侧重于进一步开发一个以过程为基础的综合生物地球化学和水文模型，以加强加拿大各地林分和流域尺度上的能量、水、碳和养分循环的预测能力。它将在现有建模工作的基础上，将碳和氮耦合的加拿大陆面计划加拿大陆地生态系统模型(CLASS-CTEM-N+)纳入MESH水文系统，以开发一个称为MESH-CTEM的综合水文和生物地球化学模型。量化管理森林对气候变化的反应将有助于环境规划者制定气候采用的森林管理做法。Mesh-CTEM建模工作将能够探索加拿大各地不同流域和气候带的加拿大森林在气候变化下的干扰(管理和/或火灾)后的生长轨迹。进一步开发CLASS和CTEM模型将有助于提高加拿大区域和全球气候模型的预测能力，如加拿大地球系统模型(CAN-ESM)，并为联邦政府的政策制定提供一个评估工具，以生成未来气候情景。

Canada's forest ecosystems, which represent about 40% or 397 Mha of the country' surface area, are being severely affected by climate change and extreme weather events such as droughts, flooding, and heatwaves. Climate warming is therein accelerating the hydrological cycle, thereby altering the growth, water balance, disturbance regimes (insect, fire), soil plant nutrient cycling and associated feedbacks (IPCC 2013, 2018). Changes in the composition, structure and functioning of forest ecosystems can affect regional climate and hence enhance the vulnerability of water resources and human communities. Developing a clear understanding of functioning of forest ecosystems and their response to climatic change and extreme events is urgently needed to maintain (or enhance) their capacity to sequester atmospheric CO2, and preserve ecosystem services. This proposal will investigate the impact of changes in forest hydrology and nutrient cycling on the carbon sequestration potential of three different age conifer and a deciduous forest and explore how these forests will respond to future climate change and extreme weather events. It will assess how different forest management treatments (e.g. variable retention harvesting (VRH)) will impact the forest growth trajectory, energy exchanges, hydrological processes in response to future climatic stresses and extreme events (e.g. drought, heat). This research will utilize ground based (e.g. eddy covariance, soil CO2 efflux, sapflow, biometric) and airborne (e.g. drone and satellite remote sensing) datasets to explore, how different age- and -species forests as well as management regimes (thinning intensities and spatial patterns) influence stand water use and productivity and response to extreme events and environmental variability. Proposal will also focus on to further develop a process- based integrated biogeochemical and hydrological model to enhance predictive capabilities of energy, water, carbon and nutrient cycles at stand and watershed scales across Canada. It will build on existing modelling work where C and N coupled Canadian Land Surface Scheme Canadian Terrestrial Ecosystem Model (CLASS-CTEM-N+) has been incorporated in the MESH Hydrological system to develop an integrated hydrological and biogeochemical model, called MESH-CTEM. Quantification of the responses of managed forests to climate change will help environmental planners to develop climate adopted forest management practices. MESH-CTEM modelling work will allow exploration of post-disturbance (management and/or fire) growth trajectories of Canadian forests under climate change in different watersheds and climate zones across Canada. Further development of CLASS and CTEM models will help to advance predictive capabilities of the Canadian regional and global climate models such as Canadian Earth System Model (Can-ESM) and provide an assessment tool to generate scenarios of future climate for policy development by the Federal Government.