Distribution

Endemic to three islands that make up Norfolk Island (Australia) which includes Norfolk Island itself, and the two nearby islands of Phillip Island and Nepean Island. On Norfolk Island itself, natural forests are largely restricted to the Mt Pitt (316m) area within the Norfolk Island National Park. On Phillip Island, a 4km² small island 6km south of Norfolk Island, the natural vegetation was largely destroyed by rabbits and other introduced animals by the 1970s and almost all Araucarias were lost. There are also historical records of its presence on the tiny limestone island of Nepean (10.5ha) off the south coast of Norfolk Island. In the early 1790s, about 200 mature trees grew there but by 1840 these had been reduced to one live and one dead tree; these appear to have persisted in some state until the late 1930s (Norfolk Island Parks and Forestry Service 2003). Currently there are no Araucarias on this small island.

The total extent of occurrance (EOO) is less than 100km². The main natural stands on Mt Pitt cover an area of less than 400 hectares giving a minimum area of occupancy (AOO) (using standard IUCN 4km² grid cells) of 4km². Fragments of natural stands also occur in other parts of the island so that the total AOO would be more than 10km². However, it cannot be more than 38km² as this is the combined total area of both Norfolk Island and Phillip Island.

Prior to the arrival of European settlers in 1788, Araucaria-dominated forests occurred in almost all parts of Norfolk, Nepean and Phillip Islands. Over the last two centuries the vast majority of the native vegetation has been cleared or degraded so that less than 10% remains. However, this does not equate to a similar reduction in the size of the Araucaria population as during this period, sporadic natural regeneration has occurred in areas not subject to grazing. Additionally, many trees and groves have been planted and some of these have become self maintaining (e.g. Hundred Acres Reserve).

Habitat and Ecology

The original vegetation on Norfolk Island was an evergreen subtropical forest with angiosperm trees and tree ferns 10–20m high, over which A. heterophylla emerged at least 30m and occasionally taller. The really large trees have all been felled, but evidence of trees with a diameter at breast height (d.b.h.) of around 3m still existed in the 1920s and large trees have now again reached in excess of 1m d.b.h. and 35–45m in height. Common angiosperm trees are (were) Olea apetala , Elaeodendron curtipendulum, Celtis paniculata, Streblus pendulinus, Lagunaria patersonia, Acronychia simplicifolia, Zanthoxylum blackburnia, Rhopalostylis baueri, Meryta angustifolia, Baloghia inophylla, Dysoxylum patersoni as well as the tree ferns Cyathea australis and C. brownii. This type of forest is now fragmented and very restricted in its distribution on Norfolk Island. Araucaria heterophylla also persists as solitary trees on coastal headlands or in groves with a low undergrowth of mostly grasses or of open scrub, with many introduced species.

Conservation Status

Global status and rationale

Vulnerable D2

Araucaria heterophylla has a naturally limited extent of occurrence (EOO) and area of occupancy (AOO). While there has been a significant past reduction in population size, the extent of this reduction is very difficult to quantify. Despite ongoing problems with invasive species and relatively recent problems with dieback, there is insufficient evidence of current decline. However, its restricted distribution and dependence on continued conservation programmes to limit the impacts of invasive species indicate that an assessment of Vulnerable is warranted.

Global threats

Logging has been a threat in the past. Land clearance and grazing have also been significant threats in the past but are now less problematic. The impact of introduced invasive species has been significant: rabbits, goats and pigs were responsible for the loss of almost all vegetation on Phillip Island while exotic trees such as Psidium cattleianum and Olea europaea ssp. cuspidata have colonised many areas on Norfolk Island itself to form dense impenetrable thickets. In the 1970s many Araucaria trees suffered from a dieback that was associated with habitat degradation and adverse environmental conditions. Improvements in land management practices, the introduction of a biological control and the removal of invasive species have led to a lessening of this problem although invasive species are still a major and ongoing threat.

Conservation Actions

The majority of the remaining natural stands are within the Norfolk Island National Park. A range of public and private restoration activities is being undertaken that is aimed at increasing the extent of the natural vegetation through replanting and invasive species control and removal. The natural vegetation of Phillip Island is slowly recovering following the elimination of goats and pigs in the 1920s and the more recent removal of rabbits.