Does drought advance the onset of autumn leaf senescence in temperate deciduous forest trees?

Abstract

Abstract. Severe droughts are expected to become more frequent and persistent.\nHowever, their effect on autumn leaf senescence, a key process for deciduous\ntrees and ecosystem functioning, is currently unclear. We hypothesized that\n(I)\xa0severe drought advances the onset of autumn leaf senescence in temperate\ndeciduous trees and (II)\xa0tree species show different dynamics of autumn\nleaf senescence under drought. We tested these hypotheses using a manipulative experiment on beech saplings\nand 3\xa0years of monitoring mature beech, birch and oak trees in Belgium.\nThe autumn leaf senescence was derived from the seasonal pattern of the\nchlorophyll content index and the loss of canopy greenness using generalized\nadditive models and piecewise linear regressions. Drought and associated heat stress and increased atmospheric aridity did not\naffect the onset of autumn leaf senescence in both saplings and mature\ntrees, even if the saplings showed a high mortality and the mature trees an\nadvanced loss of canopy greenness. We did not observe major differences\namong species. To synthesize, the timing of autumn leaf senescence appears conservative across\nyears and species and even independent of drought, heat and increased\natmospheric aridity. Therefore, to study autumn senescence and avoid\nconfusion among studies, seasonal chlorophyll dynamics and loss of canopy\ngreenness should be considered separately.