Colonisation of podocarp coarse woody debris by decomposer basidiomycete fungi in an indigenous forest in the central North Island of New Zealand

Populations of basidiomycete fungi were determined in fallen trees of two species (rimu, Dacrydium cupressinum and matai, Prumnopitys taxifolia) in a dense podocarp forest in the central North Island, in order to assist in explaining observed patterns and rates of decay. Fungi were isolated from discs cut at measured intervals along the stems of 8 trees of each species that had been studied 16 years previously. Yields of basidiomycete cultures were greater 20 years after windfall than after 4 years at radial depths exceeding 6 cm within the rimu stems, but were not significantly different beyond 12 cm in most matai trees, in which the heartwood was more resistant to colonisation. Certain basidiomycete species were associated with specific decay patterns. Prominent in both hosts were Armillaria novae-zelandiae, Ganoderma cf. applanatum, and less frequently, in the outer wood, Sistotrema brinkmannii and Hyphodermopsis polonensis. Armillaria limonea and Rigidoporus concrescens were also important towards the periphery of rimu stems. G. cf. applanatum had penetrated right to the centre of many rimu and some matai stem segments after 20 years, and large woody perennial fruitbodies present on 9 study trees were a reliable predictor of internal colonisation by this species. Presence and absence disparities between the 4- and 20-year samplings suggested that some less common basidiomycetes showed successional trends. In a more intensive examination of one tree of each species, G. cf. applanatum occupied the rimu stem in the form of multiple sets of longitudinally elongated single-genet dikaryotic colonies separated by brown pseudosclerotial plates. Genets were unique to each stem segment, indicating that colonisation occurred by means of basidiospores after the earlier sampling. On the other hand, one genet each of A. novae-zelandiae (in matai) and A. limonea (in rimu) extended to more than one segment, implying some vegetative spread, either before the first sampling or subsequently by means of rhizomorphs in soil or litter. Future research will investigate how these basidiomycete populations compare with those in the same and other tree species in relation to rates of decomposition on different sites.