Explaining links between structure, albedo and nitrogen availability in forests using LiDAR and modelling

森林冠层是由不同角度、不同密度、不同形态特征和不同光合作用能力的树叶组成的复杂排列。了解适当水平的模型复杂性并应用数学方法准确计算气体交换仍然是生物圈-大气相互作用的一个重要课题。例如，当前的全球光合作用模型仍然高度不确定，范围在100到170 PGC之间，这是生态系统、碳循环和耦合气候模型的主要输入。如果我们要对森林对气候变化的反应和气候的潜在反馈做出可信的预测，我们需要做得更好。考虑到森林在未来碳市场计划中作为信用额度的认可作用，了解推动树木吸收二氧化碳的规模敏感机制也具有经济意义。这项研究计划的目的是使用激光雷达技术来研究树冠中的树叶如何跨越强烈的环境梯度共同作用，以确定二氧化碳和与大气的能量交换。激光雷达仪器使用在扫描运动中发射的数百万个激光脉冲来确定物体在其视场中的3D位置。这项技术可以详细描述森林树冠的几何形状，包括树叶的位置和密度。这样的描述使我们能够在虚拟植被实验室中模拟太阳光(推动光合作用的能源)和其他非生物变量与植物树冠的相互作用。这种方法有可能改变我们考虑树冠结构的方式，从简单的描述符，如树高和树冠大小，转向基于群落安排的与光合作用生产有关的描述符。这一新知识将大大有助于我们预测全球环境变化对森林的影响，以及森林应对措施在气候反馈循环中的作用。这将导致对加拿大21世纪的能源挑战做出更明智的决定。

Forest canopies are complex arrays of leaves with different angles, density, morphological features and photosynthetic capacity. Understanding the appropriate level of model complexity and applying the mathematics to compute gas exchanges accurately remains an important topic of biosphere-atmosphere interactions. For example, current models of global photosynthesis remain highly uncertain, ranging between 100 and 170 PgC, and this is the primary input into ecosystem, carbon cycling and coupled climate models. We need to do better if we are to make credible predictions about the response of forests to changing climate and potential feedbacks with the climate. Understanding the scale sensitive mechanisms driving CO2 assimilation by trees also has economic ramifications considering the ratified role of forests as credits in future carbon market schemes. The aim of this research program is to use LiDAR technology to investigate how leaves in a canopy function together across strong environmental gradients to determine CO2 and energy exchanges with the atmosphere. LiDAR instruments use millions of laser pulses emitted in a scanning motion to determine the 3D position of objects in their field of view. This technology allows detailed descriptions of the geometry of forest canopies, including the location and density of foliage. Such descriptions allow us to simulate the interaction of sun light (the energy source driving photosynthesis) and other abiotic variables with plant canopies in a virtual vegetation lab'. The approach has the potential for transforming the way we consider canopy structure by moving away from simple descriptors, like tree height and crown size, towards community arrangement based descriptors relating to photosynthetic production. This new knowledge will contribute significantly to our capacity to predict the effect of global environmental changes on forests, and on the role of forest responses in feedback loops with climate. This will lead to better informed decisions regarding Canada's energy challenges of the 21st century.