1 There are wide fluctuations in the floristic composition of pastures
consisting mainly of annual species in Mediterranean climatic environ
ments. This is attributed to variations in total precipitation and rai
nfall distribution patterns. 2 In order to examine the effect of autum
n drought on the floristic composition of Mediterranean annual pasture
s, soil samples with seed banks were taken from the upper and lower sl
opes of each of three pastures that differed in successional age. Half
of each sample was subjected to a simulated autumn drought treatment
while the other half received a continuous water supply (in both cases
under controlled conditions). All germinations and deaths were record
ed throughout the 2-month experimental period. 3 Only five species had
significantly different numbers of germinations between the two water
ing treatments, and in four of these germination was lower in the drou
ght-simulated treatment. Re-watering of samples from this treatment di
d not result in a second wave of germination. 4 Drought-induced mortal
ity was greater in the samples with high seedling densities. A signifi
cant negative correlation was evident between seedling density and the
water content of the pots at the end of the experimental drought. 5 T
he least drought-sensitive species were those with stem or leaf hairs
and those belonging to Crassulaceae, which show a particular adaptive
metabolism.