The Effects of Trees on Peatland Evapotranspiration Across Scales

加拿大西部寒带平原（WBP）提供了重要的生态系统服务，如水和碳储存，也代表了加拿大经济引擎的重要组成部分，通过其资源型工业（矿产开采，林业，石油和天然气），其中最重要的是油砂开发区。在WBP普遍干燥的气候中，水的可用性是有限的，这使得主导该地区的泥炭地很容易受到气候变化以及影响泥炭地生态和水文功能的强烈工业压力的影响。了解允许泥炭地生态系统有效利用可用水分的内部和外部生态水文和气候过程，对于根据气候和土地利用变化管理这些系统非常重要。文献表明，除了内部生物物理控制外，碳、能量和水的交换还会受到外部局部边界层条件的强烈影响。然而，对泥炭地的研究很少，到目前为止，大部分研究都集中在沼泽生态系统上，而不是这个气候脆弱地区的沼泽。在内部，地表覆盖变化，特别是树木密度、土壤条件和蒸散损失之间存在反馈。从外部看，湿地和林地的景观马赛克表明，泥炭地不仅为森林覆盖的高地提供水，而且森林覆盖的高地庇护了泥炭地，限制了蒸发损失。了解泥炭地如何保护自己免受水分胁迫的机制，将改善我们对这些系统如何应对气候变化的预测能力，并使我们能够设计出更强大、更有弹性的再生系统。

The Western Boreal Plain (WBP) of Canada, provides important ecosystem services such as water and carbon storage and also represents a substantial component of Canada's economic engine through its resource-based industries (mineral mining, forestry, oil and gas), the most significant of which is the oil sands development region. In the generally dry climate of the WBP, water availability is limited, making the peatlands that dominate this region vulnerable to climate variability as well as stresses from intense industrial pressures that affect peatland ecological and hydrological functioning. Understanding the internal and external ecohydrological and climatological processes that permit peatland ecosystems to efficiently use available moisture is important for managing these systems in light of climate and landuse change. The literature suggests that carbon, energy and water exchange can be strongly influenced by external local boundary layer conditions in addition to internal biophysical controls. However, little work has been done on peatlands in general and much of the research thus far has focused on bog ecosystems rather than fens in this climatically tenuous region. Internally, feedbacks exist between changes in surface cover, particularly tree density, soil conditions and evapotranspiration losses. Externally, the landscape mosaic of wetlands and forestlands suggests that not only do peatlands provide water to forested uplands, but that the forested uplands shelter peatlands, limiting evaporative losses. Understanding the mechanism of how peatlands protect themselves against moisture stress will refine our predictive capacity of how these systems will respond to climate change, as well as permit us to design more robust and resilient reclaimed systems. The overall goal of this research is to examine how the landscape has developed strategies for sustainability in this dry climate where peatlands and forests interact synergistically to overcome the barrier of little available moisture, prolonged drought periods and extensive landuse disturbance. This research will examine water use efficiency (WUE) to explore these synergistic interactions (processes) and how they operate at different scales. The following specific objectives will be addressed: (1) quantifying the small-scale (within) peatland ecohydrological feedbacks among surface energy and mass fluxes along a gradients in tree cover and disturbance; and (2) assessing large-scale landscape interactions, where ground surface morphometry and tree density/height and orientation of forested uplands (with respect to aspect and wind direction) influence peatland evapotranspiration. This research will address the above knowledge gap and improve models for predicting the response of this region to climate warming and human disturbance at scales of importance to policy and management.