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Harvard Forest Symposium Abstract 2011

• Title: Sources of Variability in Canopy Reflectance and the Convergent Properties of Plants—Integrating Remote Sensing and Ecological Theory toward Improved Model Parameterization and Validation
• Primary Author: Scott Ollinger (University of New Hampshire - Main Campus)
• Additional Authors: Michelle Day (University of New Hampshire - Main Campus); David Hollinger (USDA Forest Service); Lucie Lepine (University of New Hampshire - Main Campus); Mary Martin (University of New Hampshire - Main Campus); Andrew Richardson (Northern Arizona University); Haley Wicklein (University of New Hampshire - Main Campus)
• Abstract:

  In a recent study involving Ameriflux data, field measurements and remote sensing, we showed that the well-known relationship between leaf-level photosynthesis and foliar %N also scales to whole canopies over continental scales (Ollinger et al. 2008). We also found that both C assimilation and canopy %N were strongly and positively related to shortwave surface albedo in temperate and boreal forests. This pattern has since been demonstrated using independent sources of data that include grasslands and crops as well as forests (e.g., Hollinger et al. 2010). These results have potentially important implications for climate modeling because they suggests a greater coupling between carbon, nitrogen and energy fluxes than has previously been recognized. However, resolving underlying mechanisms of the relationship is important because different potential mechanisms carry different implications for responses under future scenarios of change.
  
  
  
  Our current work on this topic focuses on (1) examining the C-N-albedo relationship across a broad range of spatial scales and gradients of disturbance and recovery, and (2) examining sources of variability in canopy reflectance related to leaf and canopy level traits (Ollinger 2011). We also consider the role of convergence in plant functioning and the difficulty of identifying individual drivers of spectral properties among a suite of interrelated traits. A pattern that emerges suggests a synergy among the scattering effects of leaf-, stem- and canopy-level traits that becomes accentuated in the near-infrared (NIR) region ( Fig. 1). An interesting related observation is that the factors that most affect reflectance—e.g., leaf structure, leaf angle distribution—are those that are most difficult to measure or estimate (Fig. 2). The inter-relationships of multiple plant traits that each have an effect on reflectance poses a serious challenge for remote detection of specific plant properties. At the same time, it suggests an emergent property of ecosystems that results from optimization of plant form and function across multiple scales (Fig. 3).
  
  
  
  Although measuring canopy structural properties is challenging, future work will consider variables such as leaf arrangement and foliage clumping, leaf angle distribution and crown geometry in conjunction with leaf traits and canopy spectral properties.
  
  
  
  Citations
  
  Hollinger, D.Y. et al. (2010). Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration. Global Change Biology 16, 696–710.
  
  
  
  Ollinger, S.V., et al. (2008). Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks. PNAS 105(49), 19335-19340.
  
  
  
  Ollinger, S.V. (2011). Sources of variability in canopy reflectance and the convergent properties of plants. New Phytologist 189, 375-394.
  
  

• Research Category: Regional Studies


• Figures:
Fig1.pdf
Fig2.pdf
Fig3.pdf