Seed release without fire in Callitropsis guadalupensis, a serotinous cypress of a Mediterranean-climate oceanic island

Serotiny refers to seed storage in fruit structures for more than one year within the canopy until an environmental factor triggers seed release. If the environmental cue signals improved conditions for seedling establishment, the trait can be adaptive and become evolutionarily selected. Fire has been widely recognized as a major environmental cue for serotinous conifers, although other mechanisms of seed release have been identified. I hypothesized that in Callitropsis guadalupensis, a serotinous cypress living in an oceanic island free of wildfires, the cue for seed release must be other than fire. I compared the aperture behavior of detached cones in C. guadalupensis and Callitropsis forbesii, a closely related species living in a fire-prone environment, under experimental dry conditions and in the absence of high temperatures. The results showed that after six months, more than 90% of C. guadalupensis cones opened in contrast to 33% of C. forbesii. Occurrence of seedling recruitment only in edges and forest gaps suggest that cone opening in C. guadalupensis triggered by the simple drying of the cone may be an adaptive response to tree-fall that allowed massive seed release and subsequent seedling establishment in the gaps so formed in the forest.