Effects of the sequence wildfire-clearcutting-thinning on nutrient export via streamflow in a small E. globulus watershed

Water yield and nutrient exports via streamflow were monitorized for twelve years (1987-1999) in a small experimental E. globulus watershed subjected to intensive forest management in the NW of Spain. During the period of study the watershed was severely affected by a wildfire and this gave the opportunity to evaluate the influence of this perturbation and the subsequent clearcutting and thinning, on the nutrient exports via streamflow. The wildfire caused a significant increase in nutrient exports in streamflow during the first two following years while no signif icant effect was observed the third year after wildfire. After clearfelling, inputs via precipitation compensated for nutrient exports in streamflow, except for K the first year following harvest and NO3 – during the three years after this operation. Thinning had less effect on nutrient exports than wildfire or harvest. Increased nutrient concentrations in streamflow and imbalances did not last in time, although dissolved nutrient losses measured in this study threaten forest sustainability in these plantations in intensively managed plantations growing in low fertility soils. Consequently, wildfire being the triggering perturbation for subsequent nutrient loss, fire preventive actions are critical for the sustainability of these stands. Key words: forest fire; clearcutting; solute loss; atmospheric input. Resume