Comparative leaf decomposition within the holm oak complex

The decomposition of helm oak leaves was compared using material embracing the genetical range of the helm oak complex. Collection sites were located in Morocco (Quercus rotundifolia), in the French Provence (Q. ilex), and in the French Languedocian coast (Q. ilex x rotundifolia). Leaves (living and senescent) were taken directly on the tree and in the litter at five decomposition stages. The areal weight was used to follow the loss in weight of leaves in the course of their senescence then of their decomposition in order to overcome limitations of the litterbag method. Leaves of Q. rotundifolia had a higher areal weight in their living stage but they lost more weight in the course of decomposition than leaves of Q. ilex. Leaves from hybrid populations had an intermediary behaviour. All three populations of leaves exhibited an increase in weight during senescence. At the white-rot stage (stage V), leaves of every origin reached a similar areal weight. Reasons for the observed resemblance and discrepancies have been discussed in the light of existing knowledge. Our results give additional strength to the separation of Q. ilex and Q. rotundifolia as two distinct species, with possible introgression and hybridization in contact zones. (C) 2000 Editions scientifiques et medicales Elsevier SAS.