Ecosystem processes within a Phytophthora taxon Agathis (PTA) affected kauri forest

Abstract

The novel Phytophthora species Phytophthora taxon Agathis (PTA) kills kauri seedlings and trees of all ages and is present in many of the remaining kauri stands throughout Auckland and Northland. I investigate carbon fluxes and understory plant communities within a kauri stand affected by PTA in the Waitakere ranges. Litter fall, tree growth, soil CO2 efflux and microclimatic parameters were measured fortnightly from March to September 2013, in the vicinity of trees grouped into two infection ‘classes’: (1) healthy to minimally infected and (2) medium to highly infected. Understory plant community composition survey and litter depth measurements were conducted under each tree within each of the two infection classes. Canopy density measurements were conducted under each tree using canopy photography. The amount of litter collected between March and September was considerably lower under highly infected trees than under minimally infected trees. Lower amounts of kauri reproductive material were found under highly infected trees. No differences were found in soil CO2 efflux between infection classes. Differences in photosynthetically active radiation (PAR) and throughfall were found between infection classes, resulting in changes in plant species abundance. No differences in forest floor litter depth were obtained. An understanding of the consequences of PTA for ecosystem processes is crucial to improve our understanding of pathogen related disturbances and to inform future management decisions.