Changes in water yield after a sequence of perturbations and forest management practices in an Eucalyptus globulus Labill. watershed in Northern Spain

Abstract

An experimental study to assess the effect of the sequence wildfire–clearfelling–coppice sprout selection–foliar damage caused by a defoliating beetle ( Gonipterus scutellatus Gill.) on seasonal water yield in an Eucalyptus globulus Labill. watershed was carried out in Galicia (NW Spain) from 1987 to 2005. The effect on water yield of a sequence as described in this investigation had not been evaluated till now. A summer wildfire in 1989 caused a mean increase in annual streamflow of 68%, compared with the expected value, during the first three post-fire years. After a clearfelling in 1992 a mean increase of 73% in the annual streamwater was measured for the three following years. A mean increase of 47% in streamflow was observed in the three years after coppice sprout selection in 1995. No effect in streamflow was detected the fourth year after this forestry operation. Finally, a G. scutellatus pest attack resulted in a significant average increase in annual streamwater of 22% from 1999–2000 to 2004–2005. The seasonal deviations (observed minus predicted values) in streamwater during the study period were significantly correlated with precipitation and its seasonality that explained 70% of variation in water yield deviations. Most of significant deviations were measured in autumn and winter. In no case was an increase in water availability observed during summer. No evidence of cumulative effect of those successive perturbations was found. The results presented here could help to evaluate the hydrological consequences of current intensive forest management and frequent perturbations that are affecting E. globulus stands in NW Spain. They might also be used by forest managers to understand the relationship between forest cover and water yield in the context of climate change and reduced rainfall.