leading to very low seedling survival rates. The passage of fire, however, reduces competition by clearing out undergrowth, and results in an ash bed that temporarily increases soil nutrition; thus the survival rates of post-fire seedlings is greatly increased. Furthermore, releasing a large number of seeds at once, rather than gradually, increases the possibility that some of those seeds will escape predation. Similar pressures apply in Northern Hemisphere conifer forests, but in this case there is the further issue of allelopathic leaf litter, which suppresses seed germination. Fire clears out this litter, eliminating this obstacle to germination. Evolution Serotinous adaptations occur in at least 530 species in 40 genera, in multiple (paraphyletic) lineages. Serotiny likely evolved separately in these species, but may in some cases have been lost by the related non-serotinous species. In the genus Pinus, serotiny likely evolved because of the atmospheric conditions during the Cretaceous period. The atmosphere during the Cretaceous had higher oxygen and carbon dioxide levels than our atmosphere. Fire occurred more frequently than it does currently, and plant growth was high enough to create an abundance of flammable material. Many Pinus species adapted to this fire-prone environment with serotinous pine cones. A set of conditions must be met in order for long-term seed storage to be evolutionarily viable for a plant: The plant must be phylogenetically able (pre-adapted) to develop the necessary reproductive structures The seeds must remain viable until cued to release Seed release must be cued by a trigger that indicates environmental conditions that are favorable to germination, The cue must occur on an average timescale that is within the reproductive lifespan of the plant The plant must have the capacity and opportunity to produce enough seeds prior to release to ensure population replacement Serotiny must be heritable References Plant morphology Plant physiology