How can heat and smoke stimulate seed germination in scrubland plants?

In scrubland ecosystems, heat and smoke act as critical environmental cues that break seed dormancy, allowing plants to regenerate following a wildfire. These mechanisms ensure that germination occurs only when conditions are favorable, such as after competing vegetation has been cleared and the soil has been enriched by ash.1

Heat Stimulation

For many species, heat is a physical trigger required to initiate germination. This process functions in two primary ways:1
* Melting Protective Barriers: Some plants, such as Banksia and lodgepole pine, hold their seeds in woody or resin-sealed fruits. The heat of a fire physically melts the resin or opens these structures, allowing the seeds to be released onto the newly fertilized, ash-covered ground.21
* Breaking Seed Coat Dormancy: Other species possess hard, impermeable seed coats that prevent water uptake. Exposure to high temperatures—such as the 90° to 95° C (194° to 203° F) required by the Californian chamiso (Adenostoma fasciculatum)—breaks this dormancy, enabling the seed to absorb moisture and begin growth.31

Smoke Stimulation

Smoke provides chemical signals that awaken seeds stored in the soil seed bank. The primary stimulus is a compound called karrikin, a butenolide derived from the burning of cellulose. This chemical acts as a germination trigger, allowing plants to remain dormant for decades until a fire provides the necessary conditions for them to thrive.213