Losing a foundation species: forest dynamics under kauri dieback

Keywords: forest dynamics, disease, Agathis australis, foundation species
Session Type: Virtual Paper
Day: Wednesday
Session Start / End Time: 4/7/2021 01:30 PM (Pacific Time (US & Canada)) - 4/7/2021 02:45 PM (Pacific Time (US & Canada))
Room: Virtual 9

Abstract

Foundation species dominate many forests through their exceptional biomass and ecosystem influences. How do such forests change when foundation species are lost? In New Zealand, kauri (Agathis australis) acts as an important foundation species but is currently in decline from a novel pathogen (Phytophthora agathidicida). Specific questions we sought to answer were how A. australis ecosystems are changing as a result of infection and how quickly does the disease spread within stands. We compared plant composition and structure in samples of infected and uninfected A. australis forest to indirectly indicate potential impacts. We also followed changes occurring in several large (50m x 40m) plots over five years within infected A. australis stands to investigate the epidemiology of this disease. Infected and uninfected stands showed distinct compositional dissimilarities that were not related to environmental differences. Change in stands monitored over five years indicated relatively slow disease progression with marginal changes to tree health but little additional tree mortality. A. australis populations retained individuals in all size classes including seedlings and saplings, and symptomatic and asymptomatic individuals were often close neighbours. Consistent reductions (e.g. Leucopogon fasciculatus) or increases (e.g., Dacrydium cupressinum) in abundance of other species indicate the identity of further candidates for investigation as alternative hosts, and new potential dominants in the post-disease forests respectively. It is not yet clear whether A. australis will persist long-term in these forests with diminished influence or be eliminated.