The tortoise and the hare? Post-fire regeneration in mixed Eucalyptus - Callitris forest

Abstract

Seedling regeneration after a high intensity wildfire was assessed in a mixed forest dominated by Eucalyptus species and Callitris endlicheri (Parl.) F.M. Bailey. Patterns were compared against the ‘slow seedling’ or ‘tortoise-and-hare’ theory of competitive interactions between gymnosperms and angiosperms. Browsing effects were documented using fenced plots, and seedling density, mortality and height were assessed over 6 years, from 2004–10. Consistent with expectations, Eucalyptus seedlings grew faster than Callitris seedlings in most situations. Callitris seedlings grew faster and produced seed cones sooner in plots with fewer Eucalyptus seedlings compared with plots with dense Eucalyptus seedlings. The local growth rates of Callitris seedlings were not associated with long-term site suitability for Callitris, as many plots with diminutive Callitris seedlings and dense Eucalyptus seedlings were dominated by Callitris trees before the 2003 fire. Contrary to expectations, few Callitris seedlings died during the 6-year period, so competition during the regeneration phase did not regulate co-existence. Strong drought tolerance and the ability to persist in dense, unthinned stands may enable Callitris to persist beneath dense Eucalyptus regeneration. Nevertheless, Callitris seedlings growing with dense Eucalyptus seedlings have a longer primary juvenile period than seedlings in sites with fewer seedling or adult eucalypts, which places these stands at greater risk of mortality in future fires and greater risk of browsing in the meantime.