Distribution of <i>Armillaria luteobubalina</i> and its Impact on Community Diversity and Structure in <i>Eucalyptus wandoo</i> Woodland of Southern Western Australia

Abstract

Armillaria luteobubalina Watling &amp; Kile is causinghigh mortality in Eucalyptus wandoo Blakely woodland that receives low annual rainfall of 500–700 mm, and it is a significantdisturbance agent affecting community structure. Discrete disease centresranged from 0.01 ha to 8 ha in size (mean 1.2 ± s.e. 0.3 ha) and had adiscontinuous distribution within the woodland. For 38 disease centres, thetotal area infested was 46.25 ha. Infection caused death of overstorey polesand veterans creating disease centres of greatly reduced biomass. Thisreduction was reflected by a negative correlation between the mortality ofoverstorey and basal area and diameter at breast height over bark (DBH). Theaverage mortality of E. wandoo trees was 47% indisease centres of intermediate impact, compared with 66% for highimpact areas. Regeneration of the host species increased following diseaseexpression, as evidenced by: significantly greater understocking oflignotubers and saplings in disease centres than in non-infested woodland,less bare ground in disease centres than in non-infested woodland, and apositive correlation between the mortality of overstorey and live understorey.By contrast, plant species richness and diversity did not differ significantlybetween infested and non-infested woodland. The severity of A. luteobubalina infection was not strongly related tosite factors. The rate of disease extension varied considerably between yearsduring the period 1986–1994 and averaged 2.04 ± s.e. 1.05 myr-1. Of the 26 host species recorded, 23% werefrom the Proteaceae followed by a smaller percentage from the Myrtaceae andPapilionaceae (15% each). The high impact of A. luteobubalina in E. wandoo woodland reflects the high susceptibility of the dominant host to infectionand survival strategies of the pathogen population in the harsh woodlandenvironment.