The ecological impacts of introduced fungal species, apart from plant pathogens, have been largely ignored.
The consequences of non-pathogenic exotic fungi invading indigenous ecosystems may be far-reaching. Such fungi could displace native species from the communities in which they occur, disrupt natural fungal successions in these communities, and disrupt the food chains of indigenous insects.
Although few exotic fungi are known to have invaded indigenous forests in New Zealand, the ectomycorrhizal Amanita muscaria and the wood-rotting Favolaschia calocera provide two examples. Both were introduced to New Zealand in historically recent times, and both are invading indigenous forests at some sites.
These two fungi provide ideal models to investigate the biological attributes of successful invaders, and their impact on indigenous ecosystems. Features such as:
- rate of colonisation,
- competitive ability,
- environmental tolerance,
- host specificity,
- and genetic structure of the population,
can be compared experimentally with those of native ectomycorrhizal and wood-rotting species. Direct surveys can be used to assess the impact of the invasive species on the biodiversity of native species in colonised habitats.
Before 1997 this fungus had been reported from native forest only at 3 – 4 sites in the Nelson Lakes National Park. Records gathered this year suggest it is widespread in indigenous forests in the northern half of the South Island. In most localities where it occurs, Amanita muscaria is present at numerous separate sites. This distribution might be explained by some feature of the environment or the fungus or the host in these localities, or may be a result of local spread subsequent to a single invasion. All records have been under Nothofagus spp., with no reports of it in association with the only other indigenous ectomycorrhizal trees in New Zealand, Leptospermum scoparium or Kunzea ericoides.
During the survey, Favolaschia calocera was reported from 160 individual sites around the country. Favolaschia calocera has been known in New Zealand for only 30 years, and had been thought to be still expanding its range southward. However, the known southern limit of this fungus was extended only a few kilometres. There are many species of fungi known from the tropics that show a similar geographic range in New Zealand. Whether further spread of this species is being limited by climate will be tested using a climate-matching programme.