¿Condiciona la estructura del monte y el crecimiento previo el decaimiento inducido por la sequía en dos especies de Quercus?

Abstract

Extreme events such as severe droughts modify forest dynamics by decreasing growth and the recovery ability. In the Mediterranean Basin, the effects of recent droughts on forests could be also amplified by rising temperatures. In addition, both stresses act on forests modified by humans, where tree size also depends on the historical use. Can the previous growth and tree size determine how trees respond to drought in two coexisting Quercus species (Q. ilex - holm oak, Q. faginea - Portuguese oak)? To answer this question we: (i) quantified the number of stems and size of each individual in a coppice affected by the 2011-2012 drought in NE Spain, (ii) reconstructed radial growth of individuals with low or high defoliation levels after the drought, and (iii) compared xylem anatomy (transversal size of vessels) between both defoliation classes in the case of holm oak. The most defoliated individuals were less tall than the less defoliated trees. In the case of holm oak, the most defoliated trees grew less in the past and formed vessels with smaller lumens. Our findings indicate that those holm oaks forming vessels of larger area and showing higher growth rates were the least vulnerable against drought. In the case of Portuguese oak, the most defoliated individuals were those showing the most negative growth responses to warm conditions in spring and summer.