Abstract. Severe droughts are expected to become more frequent and persistent.
However, their effect on autumn leaf senescence, a key process for deciduous
trees and ecosystem functioning, is currently unclear. We hypothesized that
(I) severe drought advances the onset of autumn leaf senescence in temperate
deciduous trees and (II) tree species show different dynamics of autumn
leaf senescence under drought. We tested these hypotheses using a manipulative experiment on beech saplings
and 3 years of monitoring mature beech, birch and oak trees in Belgium.
The autumn leaf senescence was derived from the seasonal pattern of the
chlorophyll content index and the loss of canopy greenness using generalized
additive models and piecewise linear regressions. Drought and associated heat stress and increased atmospheric aridity did not
affect the onset of autumn leaf senescence in both saplings and mature
trees, even if the saplings showed a high mortality and the mature trees an
advanced loss of canopy greenness. We did not observe major differences
among species. To synthesize, the timing of autumn leaf senescence appears conservative across
years and species and even independent of drought, heat and increased
atmospheric aridity. Therefore, to study autumn senescence and avoid
confusion among studies, seasonal chlorophyll dynamics and loss of canopy
greenness should be considered separately.
Detecting the onset of autumn leaf senescence in deciduous forest trees of the temperate zone