Arctic tundra ecosystems and their effects in a changing climate

加拿大北极约有三分之一的环极地冻土带，这片土地对所有加拿大人，特别是其北部居民具有特殊的文化、生物物理和经济意义。然而，北极的全球变暖正在以前所未有的速度发生，并正在推动陆地和海洋系统的重大变化，因此反馈放大变暖是不可避免的。在北极冻土带上，植被群落的变化及其与大气的相互作用将在未来变暖中发挥重要作用。因此，我们需要更好地了解这些生态系统及其在气候系统中的作用。*这项研究计划的目标是研究北极植被的组成和结构如何影响能量、水和痕量气体的交换，以改进对未来北极条件的模型预测。这项拟议的研究将继续我们对加拿大西北部达令湖附近低北极地区冻土带-大气相互作用的长期研究，在那里，我们已经测量了4个不同的生态系统(石南、矮灌木、低灌木和沼泽)，以测量生态系统尺度的能量、水和碳通量。现有的测量记录从5到13年不等。这些数据将被用来回答几个关键的研究问题。首先，我们将研究这些通量的季节内和年际变化如何响应不同时间尺度(从周到季节)的气候变化，并了解不同类型的冻土带如何对气候做出相似或不同的响应。第二，我们将把重点放在苔原水资源利用效率(WUE)上。这一重要参数将二氧化碳和水蒸气通量联系在一起，对于理解生态系统-大气反馈至关重要，特别是在植被不断变化的情况下。我们将利用我们对不同苔原类型的水汽和CO2通量的全生态系统测量，通过野外实验将水分通量划分为冠层和冠下部分，并使用复杂的生态系统过程模型来研究植被变化对WUE的影响，从而研究苔原的水分利用效率。这项研究计划的第三个方面是使用我们的测量和知识来帮助改善加拿大环境部的加拿大地球系统模型陆地表面方案中苔原植被(特别是灌木)的表现。这项研究将有助于更好地预测北极未来的气候状态及其对全球变暖的反应，并增加对北极生态系统对气候变化敏感程度的科学理解。它将为政策制定者提供关于北极生态系统的重要性和我们未来可能遇到的变化的信息，这将为改善北方居民及其社区的气候变化适应战略提供一个框架。

The Canadian Arctic contains about one-third of all circumpolar tundra and this land has particular cultural, biophysical and economic significance for all Canadians, especially its northern residents. However, global warming in the Arctic is occurring at an unprecedented rate and is driving significant changes in terrestrial and oceanic systems, such that feedbacks amplifying the warming are inevitable. On the Arctic tundra the alteration of vegetation communities and consequently their interactions with the atmosphere will play a significant role in future warming. Hence, we need to improve our understanding of these ecosystems and their role in the climate system. ***The goal of this research program is to examine how composition and structure of Arctic vegetation influences the exchanges of energy, water and trace gases so as to improve model predictions of future Arctic conditions. The proposed research will continued our long-term study of tundra-atmosphere interaction in the Canadian low-Arctic near Daring Lake, NWT, where we have instrumented 4 different ecosystems (heath, dwarf-shrub, low-shrub and fen) for measurements of ecosystem-scale energy, water and carbon fluxes. The existing measurement records vary from 5-13 years. The data will be used to answer several critical research questions. First, we will examine how intra-season and inter-annual variation in these fluxes respond to variations in climate at different time scales (weeks to seasons) and to develop knowledge of how different tundra types respond either similarly or differently to climate. Second, we will focus our efforts on tundra water use efficiency (WUE). This important parameter links carbon dioxide and water vapour fluxes and is critically important to understanding ecosystem-atmosphere feedbacks, especially under a regime of shifting vegetation. We will study WUE of tundra by using our whole-ecosystem measurements of water vapour and CO2 fluxes from the different tundra types, field experiments to partition the water flux into canopy and under-canopy components, and employ a sophisticated ecosystem process model to investigate the impact of vegetation changes on WUE. The third prong of this research program is to use our measurements and knowledge to assist in improving the representation of tundra vegetation (especially shrubs) in the land surface scheme of Environment Canada's Canadian Earth System Model. This research will aid in better predictions of future climate states in the Arctic, its response to global warming and increase the scientific understanding of how sensitive Arctic ecosystems are to climate change. It will inform policy makes about the importance of Arctic ecosystems and changes that we can expect to encounter in the future, which will provide a framework for improving climate change adaption strategies for northern inhabitants and their communities.**