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 coriaria, in Pinus halepensis forests on Mount Carmel, Israel, is restricted to the ash covered microsites under large burned pine trees, where the germination of other species is strongly inhibited. The aim of this study was to examine the effect of heat, ash cover, pH, water potential (Ψ(π)) and ethylene on germination of R. coriaria seeds, in order to identify the causes of this unique germination pattern. Pre-heating to 120-140 °C for 15 rain was essential for the induction of seed germination. Germination percentage was increased by ash cover of 1.2 and 2.4 kg m^-2 (1 and 2 cm, respectively) but inhibited by ash cover of 6.0 kg m^-2 (5 cm). Wet pine ash from a recently burned forest had pH of 10 and Ψν) of -0.26 MPa. Under such conditions the germination of R. coriaria was reduced by ca 80%. On the other hand, germination was stimulated by 0.03-0.10 p.p.m, ethylene which was released by wet ash. The post-fire germination of R. coriaria is regulated by the balance 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 Ψ(π)) caused by the ash. Its mode of dispersal by birds and these ecophysiological attributes direct germination of R. coriaria to preferred microsites under the burned canopies of large pine trees. These microsites are characterized by improved nutrition and low competition.