National Recovery Plan for the Christmas Island Spleenwort Asplenium listeri
B.1.4 Potential habitatB.1.4 Potential habitat
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B.1.4 Potential habitat
Despite the limited occurrences, ‘potential habitat’ appears to be:
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limestone rock crevices at the uppermost part of inland cliffs above terraces (or cuttings of similar structure)
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between about 110 and 255 metres elevation; and
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often beneath or near Ficus microcarpa.
Populations can easily remain undetected in this habitat, since much of the terraces and associated cliffs (particularly on the northern and southern sides) are infrequently visited. Survey of cliff-tops for populations is an extremely difficult undertaking due to inhospitable terrain and the nature of the vegetation (Claussen pers. comm.). These same factors make it difficult to assess the suitability of such areas as potential habitat for colonisation or (re)introduction.
A number of informants (Tranter pers. comm.; Hart pers. comm.) suggest that the greatest potential for new populations (or for colonisation or reintroduction) is at the inland cliff-tops of the eastern terraces, broadly facing the prevailing south-easterly trade winds which provide moisture to an otherwise very dry and exposed situation.
This is the zone with the largest area lying outside the national park and is the focus of most of the island’s recreational development (the eastern beaches) and some of the most significant infrastructure development (a new port and associated roading, and expansion of the airport), with possible expansion of phosphate mining on the inland side of cliff‑tops.
In view of this, all potential habitat (as described above) needs to be carefully surveyed for the presence of Asplenium listeri when proposed developments are assessed.
It has been suggested that potential habitat may also include artificially moist areas in the vicinity of water supply works, such as Jedda Cave and Jane-Up, within the altitude range for the species at 210 and 200 metres elevation respectively (Sewell pers. comm.). However, these sites have previously been surveyed with no Asplenium listeri being located (Claussen pers. comm.).