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Why can disturbances such as fire and flooding trigger seed-bank germination?

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Cluster of bright red seeds emerging from the cone-shaped fruit of a magnolia grandiflora, surrounded by large, glossy green leaves. — Seed Fruit and seeds of the southern magnolia (*Magnolia grandiflora*). The fruit is an aggregate of follicles, and each follicle bears a single red seed.

Disturbances such as fire and flooding act as environmental cues that trigger germination in soil seed banks by signaling that conditions have become favorable for growth or by removing physical and chemical barriers to development.1

Fire

In ecosystems prone to wildfire, many species have evolved to require fire-related signals to break dormancy. These signals include:
* Heat pulses: A surge of heat can physically weaken or crack tough seed coats, allowing for water uptake.12
* Chemical cues: Smoke and charred wood contain substances such as karrikin, a butenolide derived from burning cellulose that stimulates germination.31
* Clearing competition: Fires remove dense understory vegetation, providing bare soil and reducing competition for light and resources.4

Flooding

Flooding influences germination through moisture-related mechanisms:
* Leaching: Water can leach away chemical inhibitors present in the seed or surrounding fruit pulp that otherwise suppress growth.56
* Dispersal: For certain species, such as bald cypress, flooding provides the necessary medium for seeds to float to suitable, slightly raised areas where they can establish once the water recedes.4