Relationships between Water Use and Environmental Parameters in a Young Post-Fire Maritime Pine Stand after Precommercial Thinning

This study investigated the effect of heavy thinning in the relationships between water use and environmental variables in an 8-year-old post-fire-regenerated maritime pine (Pinus pinaster Ait.) stand in north-western Spain over two growing seasons. Three different treatment levels were selected: control (unthinned, 40,200 saplings ha(-1)), intense thinning (leaving 3,850 saplings ha(-1)), and very intense thinning (leaving 1,925 saplings ha(-1)), and sap flow measurements on ten saplings in each treatment were carried out along two growing seasons following thinning. Soil water availability, vapour pressure deficit and net radiation were continuously monitored. Sap flow density in control saplings was more related to soil moisture content, probably as a consequence of more limited soil water conditions, whereas in thinned plots, sap flow density was more related to vapour pressure deficit and net radiation. Thinned saplings showed higher stomatal conductance than control saplings as a consequence of the improvement of the growing conditions after the treatment.