Distribution of understorey species in forest affected by Phytophthora cinnamomi in south-western Western Australia
K. L. McDougall A B C , R. J. Hobbs A and G. E. St J. Hardy AA Division of Science and Engineering, Murdoch University, Murdoch, WA 6150, Australia.
B Current address: Department of Environment and Conservation, PO Box 2115, Queanbeyan, NSW 2620, Australia.
C Corresponding author. Email: keith.mcdougall@environment.nsw.gov.au
Australian Journal of Botany 53(8) 813-819 https://doi.org/10.1071/BT04203
Submitted: 6 December 2004 Accepted: 11 July 2005 Published: 14 December 2005
Abstract
The introduced soil-borne pathogen Phytophthora cinnamomi Rands infects and kills a large number of species in the jarrah (Eucalyptus marginata Donn. ex Smith) forest of Western Australia, causing great floristic and structural change. Many of the floristic changes can be explained simply by the known susceptibility of species to infection. Some common species, however, are rarely found at infested sites but are thought to be resistant to infection. It has been postulated that such species may be affected by the change in habitat caused by the death of trees, and not by P. cinnamomi directly. If this were the case, such species should cluster around surviving trees at infested sites. The occurrence of a susceptible species in the vicinity of trees surviving at infested sites has also been reported. To investigate the spatial relationship between trees and understorey species, the positions of trees and selected perennial understorey species were mapped at two sites in jarrah forest long-affected by P. cinnamomi. Random sets of plants and trees were generated and used in simulations to test whether understorey species grew closer to trees than expected. Many understorey species, both resistant and susceptible to infection by P. cinnamomi, were found to grow closer than expected to trees currently growing at the sites and closer to the trees that would have been present at the time of infestation. This suggests that not only do these trees enable some resistant species to persist at infested sites but that they also offer protection to some susceptible species against damage by P. cinnamomi. The proximity of many understorey species to trees that are likely to have appeared at the study sites since the first infestation indicates that the maintenance and enhancement of tree cover at infested sites in the jarrah forest may limit the damage caused by P. cinnamomi and assist in the protection of biodiversity.
Acknowledgments
This project was undertaken under an APRA (I) scholarship, sponsored by Alcoa World Alumina (Australia). Department of Conservation and Land Management research permits (NE 001035, SW 002739, SW 003248, SW 003744) and dieback permits (2310 and 2353—Jarrahdale District) were obtained. Mary Appleby kindly assisted with the arduous collection of field data.
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