Abstract

<jats:p>
The distribution of seed in the soil and its response to simulated fires were
examined in a population of Acacia saligna (Labill.)
H.L.Wendl. on the central coast of New South Wales (NSW). Soil seed density
was measured by excavating and sieving soil samples, and was estimated to be
1389 ± 297 seeds m–2 and 3600 ± 279
seeds m–2 at two sites within the population. Seed
density declined with depth, with 80% of the seedbank located in the
upper 6 cm of soil. The passage of fire was simulated by heating the soil
surface with a propane burner over an area of 0.25 m2
for durations of 2 or 4 min. A large percentage (88–94%) of the
seedbank remained dormant following heating. Temperatures measured in the soil
during heating showed that the 4-min treatment approximated the level of soil
heating expected during a fire in which all fine ground fuel was consumed;
therefore, the seedbank of A. saligna is unlikely to be
significantly depleted following a single fire. A frequency distribution of
the depths from which seedlings emerged was constructed using measurements of
the distance between the soil surface and the hypocotyl–radical
junction. A zone of lower than expected seedling emergence occurred from
0–2 cm, but the depth of this zone was not consistent with seed
mortality due to excessive heating. Reduced emergence from 0–2 cm may be
the result of seedling mortality due to temperature or water stress, which may
be influenced by changes in the soil structure or chemistry caused by heating.</jats:p>