Recovery of Tall Open Eucalypt Forest in South-Western Australia following Complete Crown Scorch

Lachlan Mccaw,Ted Middleton

doi:10.4996/fireecology.1103095

Abstract

AbstractWe investigated the response of overstorey and mid-storey trees in tall open forest of Eucalyptus diversicolor F. Muell., Eucalyptus jacksonii Maiden, and Corymbia calophylla (Lindl.) K.D. Hill & L.A.S. Johnson over an eight-year period following complete crown scorch by high intensity fire in March 2001. More than 90% of E. diversicolor and E. jacksonii and 85% of C. calophylla remained alive four years after fire, having replaced their crowns by re-sprouting from epicormic buds on the stems and larger branches. Mid-storey trees were more severely affected by fire with almost one third of Allocasuarina decussata (Benth.) L.A.S. Johnson stems and all above-ground stems of Agonis flexuosa (Willd.) Sweet killed back to ground level. Abundant seedling regeneration of E. diversicolor and E. jacksonii developed in the year following the fire but seedling density and stocking declined progressively over subsequent years. Survival of E. diversicolor seedlings was higher than for E. jacksonii seedlings, consistent with findings of earlier research. For both species, initial seedling densities were significantly greater within 25 m of potential seed trees, but seedling density was otherwise unrelated to the basal area of surrounding forest. Eight years after the fire, 38% of sample quadrats (4 m2) were stocked with one or more eucalypt saplings, with saplings of E. diversicolor and E. jacksonii having a mean height of 5 m. Saplings established following the 2001 fire could add a further age class to the stand provided that this cohort persists during subsequent fires. The results of our study provide further evidence to support the view that tall open eucalypt forests in south-west Western Australia rarely experience complete stand replacement even following intense fires, and that multi-aged stands are common.

Highlights

Fire has long been recognised as having a dominant role in the regeneration of tall open eucalypt forests in southern Australia (Ashton 1981)
The effect of past fires is evident in the age class distribution of tall open forests at the landscape scale, and in the structure of stands at the local scale where two or more cohorts of trees originating from significant regeneration events may be present
Monitoring the fate of particular regeneration cohorts provides scope to better understand the varied factors that may determine the pathway from seedling to mature tree

Summary

Introduction

Fire has long been recognised as having a dominant role in the regeneration of tall open eucalypt forests in southern Australia (Ashton 1981). Tall open eucalypt forests have a mature height >30 m and canopy cover of 30 % to 70 %, often with a stratum of midstorey trees and a dense understorey of shrubs. The effect of past fires is evident in the age class distribution of tall open forests at the landscape scale, and in the structure of stands at the local scale where two or more cohorts of trees originating from significant regeneration events may be present Tall open forests occupy 190 000 ha in south-western Australia, mostly within the Warren region, which is an administrative area that includes 930 000 ha of public land managed primarily for conservation, outdoor recreation, and sustainable timber production (Figure 1).

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Results

Conclusion