Does soil seed bank diversity limit post-fire regeneration in small, fragmented, long-unburnt remnants of fire adapted vegetation?

Abstract

Soil collected from 38 sites on Kangaroo Island in South Australia, containing small remnants of senescent Eucalyptus cneorifolia-dominated mallee, was subject ex situ to both smoke aerosol and heat treatment to simulate burning. Further soil from a subset of 29 of the sites was left untreated as a control. A total of 113 native plant species and 50 introduced species germinated across all sites. Fifty-three of the native plant species that germinated were absent in the above-ground vegetation, including twelve rare or threatened species, and three species previously unrecorded from Kangaroo Island. Fourteen native species and six introduced species germinated in heat plus smoke treated soil but not in untreated soil from the same sites. Non-metric multidimensional scaling ordination indicated differences in native species composition between sites with a long history of sustained livestock grazing (“grazed” sites) and largely ungrazed sites (“ungrazed” sites). On average, significantly more native species germinated from treated soil sampled from “ungrazed” sites than were found in the standing vegetation, while for “grazed” sites this difference was not significant. This indicates the greater potential for post-fire regeneration of native vegetation from the soil seed bank of ungrazed sites than from that of long grazed sites. Both “ungrazed” and “grazed” sites contained weeds in their soil seed banks, including some species which were stimulated by heat plus smoke. This indicated that competition from weeds is potentially a problem when fire is used as a management tool to regenerate senescent understoreys.