Use of Australian Hardwoods in Heavy Structures in Southern New Zealand

Abstract

Before human settlement, New Zealand was mostly covered in forest that included large softwood and semi-hardwood trees. Early settlers, both Maori and Pakeha (European), used these readily accessible local resources for housing, defences, canoes and ships, cooking, and heating. However, despite this apparent wealth of indigenous timber, Australian hardwoods were imported for heavy engineering structures for gold mining, transport, harbours, agricultural processing and other industries. Why was this? Was it because of costs, including shipping from Australia, compared to New Zealand sources? Was it two-way trade with kauri exported to Australia? Or was it better structural timber, more durable, stronger and more resistant to rot and insect or worm attack? This paper mainly covers the period between the gold rushes of 1860s and the great depression of 1929 - a time when many heavy structures were built in southern New Zealand with Australian hardwoods. These include Central Otago gold stamper batteries; gold dredges; the Clifden and other suspension bridges (stiffening truss); Oamaru harbour wharf structures; and the Port Craig viaducts. Uses and needs of such structures have changed over the last 100 years or so, determined by finite life cycles, deterioration, redundancy and neglect as they no longer meet changing standards or are uneconomic to maintain. Some structures have been lost, others are under threat, but some are recognised for their heritage value or adapted for other uses. Less new timber is imported now for these purposes, but there is still a need to maintain many existing structures or restore others for ongoing use or for heritage purposes. However, alternative timbers and other materials are also used. There are ongoing challenges for heritage managers and engineers, as discussed later in the paper.