Changes in the wild vascular flora of Tiritiri Matangi Island, 1978–2010

Tiritiri Matangi Island (‘Tiri’) in the Hauraki Gulf of the northern North Island of New Zealand was deforested, pastorally farmed, and then farming was abandoned in 1972. This history is typical of many northern New Zealand islands. The island’s modern history is less typical; since 1984 it has been the focus of a major restoration project involving thousands of volunteers. No original forest remains, but grazed secondary forest in a few valley bottoms covered about 20% of the island when farming was abandoned. Tiri’s wild vascular flora was recorded in the 1900s and again in the 1970s. From 2006–2010 we collated all past records, herbarium vouchers, and surveyed the island to produce an updated wild flora. Our results increase the known pre-1978 flora by 31% (adding 121 species, varieties and hybrids). A further six species are listed as known only from the seed rain; 32 species as planted only; and one previous wild record is rejected. These last three decades have seen major changes on the island: the eradication of the exotic seed predator Pacific rat, Rattus exulans, in 1993; the planting of about 280,000 native trees and shrubs during 1984–94 as part of a major restoration project along with a massive increase in human visitation; and the successful translocation of 11 native bird species and three native reptile species. More than two-thirds of the additions to the flora are exotic species, and over half of these are being controlled because of their weedy nature. The 32,000 humans who visit Tiri each year are suspected to be the main vectors of the new exotic plant species added to the flora. The recent planted forest, which covers 64% of the island, has transformed most of the former pasture and bracken fern cover; many of the exotic herbs of open areas are surviving in anthropogenic habitats (mown tracks and lawns); however, 75 species recorded during 1905–1977 appear to have become extinct. We recommend adoption of tighter quarantine requirements, control of more weed species, removal of hybrid ngaio and certain native species, more regular plant surveys, specific rare herb management, and promotion of the Hauraki Gulf threatened flora. We conclude by predicting that over the next 20 years there will be an increase in bird-dispersed seed, increase in seabird guano habitat, few new native tree species, and a continued increase in the proportion of shade-tolerant trees.