Estimation of leaf area index in open-canopy ponderosa pine forests at different successional stages and management regimes in Oregon

Leaf area and its spatial distribution are key parameters in describing canopy characteristics. They determine radiation regimes and influence mass and energy exchange with the atmosphere. The evaluation of leaf area in conifer stands is particularly challenging due to their open nature and clumping on the needle, shoot and tree scale. The overall objective of our study was to characterize leaf area index (LAI) (Lh, m2 half-surface area foliage m-2 ground) in the vicinity of our old-growth and 14-year-old ponderosa pine (Pinus ponderosa, var. Laws) eddy covariance flux sites, with future plans to scale from the flux sites to the pine region using ecosystem models and remote sensing. From the combination of optical and canopy geometry measurements, sapwood and litter-fall measurements, and one- and three-dimensional (3-D) models, we evaluated the variation in estimates of Lh in a mixed-age stand at the old-growth flux site. We also compared sapwood area estimates from a local allometric equation with LAI-2000 estimates that have been corrected for clumping and the interception of light by stems and branches (Lhc, m2 half-surface area m-2 ground) across a range of age classes and stand densities of ponderosa pine forests along a 15 km swath in Central Oregon that encompassed the flux sites. In the old-growth stand, the litter-fall and sapwood estimates tended to be higher than the optical and 3-D radiative transfer model estimates. Across the 15 km east–west gradient from the crest of the Cascade Mountains, Lhc was typically lower than the sapwood estimates (Lhsw; slope 0.38). The Lhc data, as well as aboveground production estimates for the 17 pine plots will be useful for scaling flux measurements to the region using ecosystem models that have been validated with these data