Data from: The post-fire recovery of soil seed banks along a fire severity gradient in an Australian threatened mesic forest

Climate change has increased the likelihood of extreme events, increasing
the number of days with dangerous fire weather conditions, resulting in
fires with increased severity, frequency, and extent. This can greatly
impact vegetation communities by reducing diversity and slowing recovery.
The role of in situ soil seed banks in mediating the impacts of shifting
fire regimes is often unclear and may vary between different vegetation
types. In particular, the impact of high fire severity, an increasingly
common fire regime shift, may increase the likelihood of temperatures
lethal to seeds in the soil, while higher fire frequencies may reduce
diversity via increased immaturity risk. Here, we aim to assess how fire
severity impacts the species and functional group diversity of soil seed
banks in a threatened mesic forest community. We collected 396 soil
samples from 12 sites within a wet sclerophyll forest in the Blue
Mountains of New South Wales, Australia, that had been burnt during the
2019/2020 Australian megafires at differing fire severities (moderate,
high, and extreme), as well as from unburnt (control) sites, three years
post-fire. Soil samples were split into the leaf litter and soil, both
treated with smoke and heat to break fire-related dormancy, and regularly
watered in a greenhouse to observe germination for a year. This was
compared to floristic surveys conducted at each site. Our data showed a
hump-shaped relationship between species richness and fire severity, both
in the extant vegetation and in the soil seed bank. The lowest richness
occurred at unburnt sites increasi, increasing to a peak at moderate
severity burn sites and declining slightly at high and then extreme
severity sites. Obligate resprouters generally declined as severity
increased. A distinct difference in composition between extant vegetation
and the soil seed bank emphasises that a significant portion of the
species richness within these communities solely exists in the soil seed
bank, fluctuating as environmental conditions change. The soil seed bank
is susceptible to decline in richness when both unburnt and burnt and
extreme severities, largely impacting the composition within these
ecosystems.