Regulation of the germination of Rhus coriaria, a post-fire pioneer, by heat, ash, pH, water potential and ethylene

Germination of the post-fire pioneer species Rhus cor inr in, in Pinus hale pensis forests on Mount Carmel, Israel, is restricted to the ash covered mi crosites under large burned pine trees, where the germination of other spec ies is strongly inhibited. The aim of this study was to examine the effect of heat, ash cover, pH, water potential (psi(pi)) and ethylene on germinati on of R. coriaria seeds, in order to identify the causes of this unique ger mination pattern, Pre-heating to 120-140 degrees C for 15 min was essential for the induction of seed germination, Germination percentage was increase d by ash cover of 1.2 and 2.4 kg m(-2) (1 and 2 cm, respectively) but inhib ited by ash cover of 6.0 kg m(-2) (5 cm), Wet pine ash from a recently burn ed forest had pH of 10 and psi(pi) of -0.26 MPa. Under such conditions the germination of R, coriaria was reduced by ca 80%, On the other hand, germin ation was stimulated by 0.03-0.10 p.p.m, ethylene which was released by wet ash, The post-fire germination of R, cor inr ia is regulated by the balanc e between the stimulating effects of fire heat and the ethylene released by the ash, and the inhibition caused by the high pH and the low psi(pi) caus ed by the ash, Its mode of dispersal by birds and these ecophysiological at tributes direct germination of R. coriaria to preferred microsites under th e burned canopies of large pine trees, These microsites are characterized b y improved nutrition and low competition.