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

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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.