Remote sensing of PAR interception and net primary production in trembling aspen and black spruce stands

A series of LANDSAT spectral vegetation index images, calibrated to a common reference image, were used to model the phenological dynamics of 30 quaking aspen (Populus tremuloides) and 29 black spruce (Picea mariana) stands in the boreal forest of northeast Minnesota. Phenology models of the stands were used in a simplified species-specific canopy modeling framework to estimate the amount of photosynthetically active radiation (PAR) intercepted by the canopy annually. The relationship between annual PAR interception (∑IPAR) and measured annual above-ground net primary production (AANPP), that is, the dry matter yield of ∑IPAR, was examined. Age was a primary determinant of the relationship between ∑IPAR and AANPP in aspen, with ∑IPAR in young stands exhibiting a strong predictive capability relative to mature stands. This observation is consistent with increased maintenance respiration demands as the ratio of total to foliar biomass increases with stand age. ∑IPAR was a good predictor of AANPP in spruce stands. Calculated values of the dry matter yield of ∑IPAR were within the range of literature reports for other forest ecosystems, but further research to understand the sources of between-stand variations is required, and on-going.