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, NMDS ordination based on Bray Curtis
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 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.