, Volume 7, Issue 5, pp 454–467 | Cite as

Light-transmission Profiles in an Old-growth Forest Canopy:Simulations of Photosynthetically Active Radiation by Using Spatially Explicit Radiative Transfer Models

  • Maria J. Mariscal
  • Scott N. Martens
  • Susan L. UstinEmail author
  • Jiquan Chen
  • Stuart B. Weiss
  • Dar A. Roberts


Light interception is a driving variable for many key ecosystem processes in forests. Canopy gaps, as natural irregularities, are common features of Pacific Northwest conifer forests and have profound importance on the within-canopy light environment. We used two spatially explicit radiative transfer models (OLTREE and SolTran) to understand better the vertical profile distribution of light penetration in an old-growth forest. Canopy access at the Wind River Canopy Crane Research Facility provided an opportunity to apply these models in a tall, old-growth, Douglas-fir–western hemlock forest. Both models required three-dimensional descriptions for every crown (location, orientation, and size) in a 4-ha area. Crowns were then simulated as foliage-filled ellipsoids through which light is attenuated following Beer’s law. We simulated vertical profiles (2-m height intervals) of transmitted photosynthetically active radiation (PAR) in 16 gaps previously measured by Parker (1997). Point-by-point comparisons (n = 480) between measured and modeled results showed little agreement because small errors in crown location yielded large local differences in PAR transmittance. However, average gap profiles (n = 16) of PAR transmittance showed excellent agreement (r2 = 0.94) between simulated and measured values. SolTran was used to simulate vertical profiles of daily PAR flux at different seasons for the whole 4-ha canopy, not just gaps. Overall, our results show that both models produced excellent simulations of spatially averaged vertical profiles of PAR transmission in the old-growth forest and are suitable for further investigations at other space and time scales.


light profiles photosynthetically active radiation (PAR) irradiance distribution radiative transfer models old-growth conifer forests forest gap structure Wind River Canopy Crane Research Facility (WRCCRF) 



This research was performed at the Wind River Canopy Crane Research Facility, a cooperative scientific venture among the University of Washington, the USFS PNW Research Station, and the USFS Gifford Pinchot National Forest. This research was supported by the Office of Science, Biological and Environmental Research Program (BER), US Department of Energy (DOE), through the Western Regional Center of the National Institute for Global Environmental Change (NIGEC) under Cooperative Agreement DE-FC03-90ER61010. Any opinions, findings, and conclusions or recommendations expressed herein are those of the authors and do not necessarily reflect the view of the DOE. We wish to thank Geoffrey G. Parker for his data and suggestions on an earlier version of this report.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Maria J. Mariscal
    • 1
  • Scott N. Martens
    • 1
  • Susan L. Ustin
    • 1
    Email author
  • Jiquan Chen
    • 2
  • Stuart B. Weiss
    • 3
  • Dar A. Roberts
    • 4
  1. 1.Center for Spatial Technologies and Remote Sensing, Department of Land, Air and Water ResourcesUniversity of CaliforniaDavisUSA
  2. 2.School of Forestry and Wood ProductsMichigan Technological UniversityHoughtonUSA
  3. 3.Center for Conservation Biology, Department of Biological SciencesStanford UniversityStanfordUSA
  4. 4.Geography DepartmentUniversity of CaliforniaSanta BarbaraUSA

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