Sapling responses to variations in gap densities and spatial configurations modeled using SORTIE

The objective of this study is to measure the sapling responses to variation in gap densities and spatial configurations in simulated stands using the SORTIE model. The hypothesis is that the cumulative effects and the interaction of several small increases in direct and diffuse light can have important effects on the growth of saplings. Four gap densities were introduced by removing trees until 10%, 20%, 35% and 50% of total basal area was removed. The configuration of the gaps surrounding the saplings was characterized by recording the gaps present in six radial distance intervals, and the number of gaps directly positioned above the saplings. The analysis of the sapling growth before and after the introduction of gaps shows an increase in basal area and in the number of growth release episodes that varies with gap density, with a stronger trend observed in shade intolerant species. Spatial analyses reveal that the combination of increases in light originating from several gaps has an important effect on saplings growth and can cause growth releases similar to those attributed to a direct gap. These results confirm the value of combining modeling and spatial analysis to study gap dynamics at fine spatial and temporal scales.