Pattern and process and the dynamics of forest structure: a simulation approach

A computer model was developed to simulate natural forest dynamics. Relationships of leaf area to sapwood area, stem respiration to sapwood volume and vigour to growth efficiency provide equations for tree growth, leaf-area dynamics and canopy structure. The model simulates mixed-age, mixed-species populations of trees on a 1000-m² patch. The test site, Fiby urskog (C Sweden), has been unmanaged since a catastrophic storm in 1795. Pinus sylvestris (light-demanding) and Picea abies (shade-bearing) are dominant today. Pinus trees are >70 yr old with high crowns. Picea are all-aged; single-tree gaps are filled by saplings or small tress of Picea. The model was run for 190 yr to simulate the natural succession. Picea abundance increased sigmoidally as its growth conditions improved, but Pinus was abundant only under conditions unfavourable to Picea. A wide range of patch sizes produced accurate simulations, but if the patch size was too small (<50 m²) the model allowed gap-phase replacement of Picea by Pinus. Such replacement was not observed. A simulation with Betula pubescens and Populus tremula included reproduced the approximate composition of the stand. Pinus, Betula and Populus (all light-demanders) were important early in the simulated succession but were eventually replaced by Picea. -from Authors