Impact of Phytophthora cinnamomi on the taxonomic and functional diversity of forest plants in a mediterranean-type biodiversity hotspot

Aim: Diversity-rich mediterranean-type sclerophyllous forests are home to 20% of described species on Earth. In the Eucalyptus marginata (jarrah) forest of southwest of Western Australia diversity is being reduced by extensive human use and the introduction of the plant pathogen Phytophthora cinnamomi. This study investigated the influence of P. cinnamomi infestation on the structure, taxonomic and functional diversity, and species composition of the forest.Location: Jarrah forest of southwestern Australia.Methods: Species abundance, understorey cover and canopy cover were assessed along 22, 30 m long transects which crossed infested and non-infested zones in five reserves in the jarrah forest. A trait database was assembled for 137 plants using 13 traits related to nutrient and carbon acquisition, disturbance tolerance and reproduction. The responses of canopy cover, understorey cover, species richness, Shannon diversity, evenness, abundance, and functional diversity for trait groups, and all groups combined were modelled against reserve and zone as fixed effects and transect and transect section as random effects. To assess the species composition, non-metric multidimensional scaling (NMDS) ordination based on Jaccard resemblance and indicator species analyses were used.Results: Significantly higher understorey cover, species richness, Shannon diversity and evenness were recorded in non-infested compared to infested zones, but there were no changes in the canopy cover and overall abundance. In non-infested zones, the functional diversity of nutrient acquisition and reproductive traits was higher, but the functional diversity of carbon acquisition traits was lower. No difference in functional diversity was recorded in disturbance tolerance and overall traits between the two zones. NMDS ordination and analysis of similarities (ANOSIM) revealed a significant difference in the species composition between the two zones, and 11 indicator species significantly associated with infested and non-infested zones were identified.Conclusion: Phytophthora cinnamomi has significantly affected the forest structure, taxonomic and functional diversity, and species composition. Contrasting responses of functional trait groups obscured overall trait responses to P. cinnamomi.