Fire intensity, serotiny and seed release in 19 woody species: evidence for risk spreading among wind-dispersed and resprouting syndromes

Abstract

Seed storage in woody fruits on plants has been much studied, whereas trait variation in seed release has been given scant attention. In non-Mediterranean climates, some species release seeds immediately after fire, whereas others retain seeds in open fruits/cones for longer. We expected that species with wind-dispersed seeds and those killed by fire would spread their recruitment risks by having stronger cues for fruit opening and slower seed release once fruits were open. We therefore tested whether fire intensity (heat) affected fruit opening and seed release in 19 species. We then contrasted fruit opening and seed release among (1) serotiny levels (weak, moderate, strong), (2) dispersal (wind v. unassisted) and (3) resprouting ability (killed v. resprout) traits. Only three species required heat for fruit opening. Most species, however, retained varying proportions of seeds in open fruits. Strongly and moderately serotinous species retained seeds in open fruits longer than did weakly serotinous species. Both species with wind-dispersed seeds and fire-killed species required stronger heat effects for fruits to open but retained seeds in open fruits longer than did species with alternative traits. By delaying seed release after fruits have opened, species with wind-dispersed seeds, and those that are killed by fire, maximise the ability of seeds to arrive at safe sites after fire.