HabitatHabitat

Habitat

Primary Rainforest (after Du Puy 1993) is restricted to the central plateau and is an evergreen closed forest 30 - 40 m high with emergent trees up to 45 m tall. 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 Aidia aff. racemosa, Arenga listeri, Leea angulata, Ochrosia ackeringae and Pisonia umbellifera (Environment Australia 1994). Primary Rainforest can be further divided into two types after Mitchell (1974): Deep-soil Tall Closed Forest and Shallow-soil Closed Forest (Type I and II forests in Orchard et al. 2002) where the limestone is close to or at the surface. Hill (1996) censused Christmas Island Hawk-Owls in homogeneous areas of both these Primary Rainforest types.

Marginal Rainforest (after Du Puy 1993) grows 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. This forest is generally lower than Primary Rainforest, often less than 30 m tall, and may include many vines. The canopy height and shape is 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 a low secondary growth closed 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. Hill & Lill (1998a) did not record owls using old minefields at all, however, they did observe owls hunting in grassy clearings.