Nothofagus (Fagaceae) and its invertebrate fauna—an overview and preliminary synthesis

Abstract

The invertebrates directly associated with the southern hemisphere tree genus Nothofagus are described and discussed in terms of their organization into guilds and attributes of their hostplants. Using literature records, comparisons are made of the guild composition between host species and provenances; a full invertebrate-hostplant list is appended. Sap-sucking Homoptera are particularly diverse and usually host-species specific whereas defoliating insects seem less prevalent and less specific. Few seed-eating insects are reported. Some provenances and hostplants exhibit local radiations in certain taxa, such as Eriococcidae in New Zealand, Notophorina psyllids in South America and scolytid beetles on N. dombeyi. Environmental stresses such as drought, disturbance and landslips, can induce outbreaks of certain scale insects and borers, affecting the dynamics of the forest. Generally, however, the influence of invertebrates appears benign, but occasional large-scale defoliation is observed on N. solandri var. cliffortioides, N. moorei, N. antarctica and N. pumilio. Collectively this fauna has two elements: a geographically recurrent Gondwanic element, usually monophagous, and a provenance-specific element (often polyphagous) locally recruited following vicariance of the host genus. The fauna of Nothofagus can be in stark contrast to that of adjacent forest types. In Australia, the insect profile of Nothofagus has more in common with fagaceous trees on other continents than the more recent Eucalyptus forests which surround it. There is almost no evidence of fauna transfer from Nothofagus to Eucalyptus. Relative to New Zealand, the Australian Nothofagus fauna is depauperate and may reflect truncation in Pleistocene glaciations. Typically low insect populations on these trees may partly explain the limited range of insectivorous birds and spiders observed in Australia. Much more data on the phytophagous insects of this biome is needed for comparative purposes. The fauna of the montane tropical subgenus Brassospora pollen group is almost unknown but could hold the key to the origin of fagaceous insect communities more generally. The conservation value of remaining Nothofagus forests is enhanced by recognition of their co-adapted fauna, some of which are arranged in stable functional groups likely to give valuable insight into invertebrate-hostplant interactions originating in the Cretaceous. Elucidation of its role in the processes of these unique forests remains a fertile field for endeavour in the future.