Simulation of primary production in even-aged stands of Douglas fir

Net primary production in even-aged stands of Douglas fir ( Pseudotsuga menziesii) (Mirb.) Franco) in The Netherlands is simulated from stand establishment after planting until harvest time. Net yearly increments of needle, branch, stem and root biomass are calculated from gross primary productivity, determined by weather conditions, photosynthetic performance of the foliage, site index, and biomass-dependent maintenance respiration. Stand structure is represented by an array of stem diameters at breast height, based on 20 percentiles of the cumulative diameter frequency distribution. Individual tree-to-tree distances are not taken into account. Spatial arrangement of the trees is assumed to be optimal with respect to interception of incoming radiation. The model incorporates a thinning management algorithm which provides for several types of thinning. Comparison of the behaviour of the model with measurements from permanent field plots in The Netherlands shows acceptable agreement of the simulation results with the experimental data. Using a simulation model, a wide variety of environmental factors combined with different management alternatives can be evaluated for their influence on forest primary production.