Effects of a Severe Drought on Water and Nitrogen Use by Quercus ilex and Phyllyrea latifolia

A severe drought that took place in Spain and other Mediterranean countries in 1994 produced a dieback of Quercus ilex trees on south-facing conglomerates but only minor defoliations in trees on north-facing schists. The foliar ¹³C of damaged trees continued to decrease in the next two wet years probably indicating increasing water use efficiency, and their ¹⁵N continued to increase indicating progressive ecosystem N saturation and/or N losses whereas there were no significant changes in undamaged trees. Pre-drought ¹³C values were reached in the third year after the drought, but ¹⁵N values did not yet recover. Another co-occurring small tree, Phyllyrea latifolia, did not show any damage and gained dominance in the most affected stands.