Season of fire influences seed dispersal by wind in a serotinous obligate seeding tree

Abstract

In temperate ecosystems, fire management involving prescribed burning and wildfire suppression often causes a shift in fire season from hot and dry summer conditions to cooler, moister conditions in spring or autumn. The effects of this change on seed dispersal by wind after fire are unknown. However, calmer wind conditions and increased standing vegetation after fires in cooler seasons may reduce seed dispersal following fire. We studied seed dispersal in different seasons for a serotinous obligate-seeder, Callitris verrucosa, growing in a semi-arid environment in South Australia. We measured primary (wind-borne) and secondary (on-ground) seed dispersal during spring, summer and autumn, using empirical observations and modelling based on detailed measurement of wind characteristics. At comparable horizontal wind speeds, primary dispersal was greater in summer compared to spring and autumn. Secondary dispersal was similarly short in all three seasons when vegetation cover was high, but when cover was low, seeds travelled much further in summer than in the other two seasons. A shift in the seasonal timing of seed release can decrease dispersal distances of serotinous obligate seeders, which is likely to reduce gene flow and the ability to colonise new sites. This can lead to changes in population and community structures which may further affect fire patterns. These findings could be applicable to other serotinous obligate seeding plant species found in other families such as Proteaceae, Myrtaceae, Pinaceae and Cupressaceae.