Effects of a severe drought on water and nitrogen use by Quercus ilex and Phillyrea 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 conglomer ates but only minor defoliations in trees on north-facing schists. The foli ar Delta(13)C of damaged trees continued to decrease in the next two wet ye ars probably indicating increasing water use efficiency, and their delta(15 )N continued to increase indicating progressive ecosystem N saturation and/ or N losses whereas there were no significant changes in undamaged trees. P re-drought Delta(13)C values were reached in the third year after the droug ht, but delta(15)N values did not yet recover. Another co-occurring small t ree, Phillyrea latifolia, did not show any damage and gained dominance in t he most affected stands.