Many chaparral species have fire-dependent regeneration, meaning that dormant seeds in the soil require a stimulus from fire for germination. A few species have hard seeds that are cracked by the heat of fire and this stimulates germination. Ceanothus seeds are a good example of this germination mode. However, for the majority of species, seeds do not respond to heat but rather to chemicals generated by the burning of plant matter. This can result from exposure to smoke or charred wood. In many of these species seeds will not germinate when placed at room temperature and watered, unless they are first exposed to smoke or charred wood. In natural environments the seeds remain dormant for decades until fire. There is evidence that a variety of chemicals in smoke and charred wood may be responsible for stimulating germination of postfire species, and both inorganic and organic compounds may be involved.
Seeds of many species have a requirement for cold temperatures (<5 °C), which is interpreted as a seasonal cue, but in these chaparral species this requirement is not like the cold stratification requirement of many species from colder climates, where the seeds require a certain duration of cold in order to prevent winter germination. In California species just a short burst of cold often will trigger germination; thus, cold is not a cue that winter is over (as with more northern latitude species) but rather that winter has arrived, which is consistent with the winter germination behavior of these Mediterranean-climate species.
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