DISTRIBUTION OF ARMILLARIA-LUTEOBUBALINA AND ITS IMPACT ON COMMUNITY DIVERSITY AND STRUCTURE IN EUCALYPTUS-WANDOO WOODLAND OF SOUTHERN WESTERN-AUSTRALIA

Armillaria luteobubalina Watling & Kile is causing high mortality in E ucalyptus wandoo Blakely woodland that receives low annual rainfall of 500-700 mm, and it is a significant disturbance agent affecting commu nity structure. Discrete disease centres ranged from 0.01 ha to 8 ha i n size (mean 1.2 +/- s.e. 0.3 ha) and had a discontinuous distribution within the woodland. For 38 disease centres, the total area infested was 46.25 ha. Infection caused death of overstorey poles and veterans creating disease centres of greatly reduced biomass. This reduction wa s reflected by a negative correlation between the mortality of oversto rey and basal area and diameter at breast height over bark (DBH). The average mortality of E. wandoo trees was 47% in disease centres of int ermediate impact, compared with 66% for high impact areas. Regeneratio n of the host species increased following disease expression, as evide nced by: significantly greater understocking of lignotubers and saplin gs in disease centres than in non-infested woodland, less bare ground in disease centres than in non-infested woodland, and a positive corre lation between the mortality of overstorey and live understorey. By co ntrast, plant species richness and diversity did not differ significan tly between infested and non-infested woodland. The severity of A. lut eobubalina infection was not strongly related to site factors. The rat e of disease extension varied considerably between years during the pe riod 1986-1994 and averaged 2.04 +/- s.e. 1.05 m yr(-1). Of the 26 hos t species recorded, 23% were from the Proteaceae followed by a smaller percentage from the Myrtaceae and Papilionaceae (15% each). The high impact of A. luteobubalina in E. wandoo woodland reflects the high sus ceptibility of the dominant host to infection and survival strategies of the pathogen population in the harsh woodland environment.