DISTANCE-INDEPENDENT MODELS FOR PREDICTING PHOTOSYNTHETICALLY ACTIVE RADIATION TRANSMISSION THROUGH YOUNG FOREST PLANT CANOPIES

We developed two distance-independent models for predicting photosynth etically active radiation (PAR) transmission through young forest plan t canopies. The two models (model 2, using individual-plant crown area , and model 3, using species cover) were derived from a more complex i ndividual-plant, distance-dependent model (model 1) described in an ea rlier study. Models 2 and 3 require fewer data inputs and can be used when detailed data on individual plants are not available and (or) spa tially explicit predictions of PAR transmission are not of interest. W e found close agreement between PAR transmission values between model 1 and models 2 and 3 using data from a plant density study. Mean predi ction errors between models 1 and 2 were 0.34% and 1.09% for two plant species studied. Mean prediction errors between models 1 and 3 were 0 .77% and 2.58% for the two plant species studied. The extinction coeff icients estimated from model 1 were used successfully in models 2 and 3 without additional calibration.