Byron B. Lamont and Juli G. Pausas
This is a plain language summary of a Functional Ecology review article which can be found here.
Seeds are fine-tuned to accept only certain environmental stimuli to break dormancy and cause them to germinate at once or allow them to germinate later. Some seeds germinate as soon as the soil is moist, warm, and aerated. Their dormancy had been forced on them by lack of such suitable conditions before then. Others are non-responsive to these favorable conditions until they have been exposed to bouts of high summer temperatures, fire-caused heat or smoke, strong leaching rains, exudates from a potential host, or digestion by animals. Thus, they are adapted to infrequent but certain events from their ancient past that herald improved conditions for germination and seedling establishment after dormancy release—they are now ready to respond to moisture, warmth and oxygen like other seeds. A third group does things in reverse: the seeds must already be under mild conditions, especially moist and aerated, before their dormancy can be broken by bouts of near-freezing temperatures (which herald a mild spring), darkness (which indicates that they are buried) or light (confined to small seeds that must be at the soil surface for establishment to succeed). These stimuli do not act in isolation but serve as alternatives or even have additive or synergistic effects.
Thus, the Californian poppy may germinate best after exposure to winter cold plus smoke. Sometimes, the environmental conditions may change before germination can commence and the seeds return to dormancy, and the procedure is repeated later (dormancy cycling). The three dormancy-release pathways, together with internal, seasonal and random interactions, are coordinated by the seed to ensure maximum germination under optimal conditions. To ignore any of these processes leads to an impoverished understanding of the wide-ranging seed ecology of species adapted to harsh and disturbance-prone environments.