Seed release without fire in Pinus halepensis, a Mediterranean serotinous wind-dispersed tree

1 Although serotiny is frequently considered to have evolved under the sele ctive pressure of fires, the drying conditions that induce cone opening are not necessarily associated with fire. We hypothesized that in Pinus halepe nsis, a Mediterranean serotinous wind-dispersed tree, xeriscence (seed rele ase induced primarily by drying conditions not generated by fire) bears int rinsic adaptive values, independent of those of pyriscence (fire-induced se ed release). 2 We used seed-traps to quantify seed release in two scrubland pine stands in Israel. Contemporary meteorological data were used to seek correlations with climatic factors affecting seed release. 3 Substantial seed release, estimated to be about 60% of the annual crop, w as observed in the absence of fire. Seed release was distinctly seasonal, w ith high rates in spring and autumn, and was strongly correlated with short , infrequent but temporally predictable Sharav events (dry and hot weather) . In the most extensive Sharav-induced seed release, seed density reached 1 17 seeds m(-2) and 15% of the annual crop was released within 6 days. Stepw ise multiple regression revealed that mean relative humidity (in both stand s) and maximum temperature (in one stand) were significant predictors of se ed release. 4 Vertical (upwards) wind velocity was significantly positively correlated with dry and hot weather. Seed counts in distant traps (> 20 m from the nea rest tree) were significantly greater in periods in which Sharav events occ urred than in other periods. Xeriscence may therefore have an adaptive valu e in promoting dispersal distance by wind. 5 Both xeriscence and pyriscence appear to be involved in determining serot iny in P. halepensis and provide means of exploiting establishment opportun ities generated either by fire or by other factors.