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 decom
position 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 ord
er to overcome limitations of the litterbag method. Leaves of Q. rotundifol
ia had a higher areal weight in their living stage but they lost more weigh
t 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 f
or the observed resemblance and discrepancies have been discussed in the li
ght of existing knowledge. Our results give additional strength to the sepa
ration of Q. ilex and Q. rotundifolia as two distinct species, with possibl
e introgression and hybridization in contact zones. (C) 2000 Editions scien
tifiques et medicales Elsevier SAS.