HabitatHabitat

Habitat

Approximately 75% of Christmas Island is still covered with natural vegetation and 84% of this (or 63% of the island) is protected within National Park (Figure 1). The remaining Primary rainforest is currently protected from clearance by a Federal Government moratorium, in conjunction with the requirements for approval under the EPBC Act and Environment Protection and Biodiversity Conservation Regulations 2000 (EPBC Regulations). Marginal rainforest and Second-growth rainforest or Secondary Vegetation outside the National Park may only be cleared if approval is given under the EPBC Act and Regulations.

Schedule 12 of the EPBC Regulations use Du Puy’s classification to describe the Christmas Island forests. Primary Rainforest is restricted to the central plateau and is evergreen closed forest 30-40m high with emergent trees up to 45m. Common canopy trees include Syzygium nervosum, Planchonella nitida, and Hernandia ovigera. The canopy formed by these trees is irregular, especially on the western side of the island where it is sheltered from strong southeast trade winds which blow throughout the dry season. The understorey comprises dense thickets of Pandanus elatus up to 4m tall, and more open areas which commonly include the plants Arenga listeri, Leea angulata, Ochrosia ackeringae, Pisonia umbellifera and Aidia aff. racemosa (Environment Australia 1994).

Marginal Rainforests grow on generally shallower soils on the coastal terraces and scree slopes surrounding the island. Many Marginal Rainforest trees lose their leaves in the dry season. Marginal rainforest is generally lower than Primary Rainforest, often less than 30m, and may include many vines. The canopy height and shape are variable, determined primarily by the degree of exposure to the southeast trade winds. Marginal rainforest facing south and east has a smooth, wind-pruned canopy and tends to increase in height with increasing distance from the sea cliff. The inland cliffs and scree slopes may have no vegetation or carry a closed forest, depending on the degree of the slope. Trees such as Ficus microcarpa and Dendrocnide sinuata are common there.

Old stockpiles and cleared areas that have not been mined may support low second-growth forest of colonising trees such as Macaranga tanarius and Claoxylon indicum and an introduced tree Leucaena leucocephala generally less than 10m high. Previously mined areas tend to have very little remaining soil and on them grow dense herblands of a fern Nephrolepis multiflora to 2m high along with introduced scramblers and occasional low trees.