High Ground in the Tropics

High mountains in tropical areas sustain a rather depauperate lichen flora consisting predominantly of species widespread in boreo-alpine areas elsewhere in the world, but also including local endemics. These species have nowhere to go, other than literally in air, in the case of global warming. The mountains in New Guinea are examples of this group. They are among the most isolated biomes, as they are not connected to temperate regions, as, for example, the Andes are. Mount Wilhelm, reaching about 4500 m, is the highest mountain in Oceania, and from a lichenological point of view is the best investigated high mountain in New Guinea. It is also the richest in lichen species, as several other mountain tops are grass-covered. This is an isolated mountain, of which only less than 100 km2 lies above the tree line and is at least partly suitable for boreo-alpine terricolous and saxicolous lichen growth. Among these are many cosmopolitan species [20,21]. The species, virtually on the equator, must be considered as 'boreo-alpine' or 'temperate' in a climatic (not geographic) sense. They cannot be considered as 'circumpolar' or 'bipolar' as is often stated [22]. For these New Guinean lichens their next closest localities are in Taiwan, over 4000 km away, and in the Himalayas, more than 5000 km away. How the species actually arrived remains unknown, although the presence of relatively many species that are associated with bird perching suggests that birds may have played an important role as vector of lichen diaspores, next to or even instead of wind and air currents.

The alpine lichen zone on Mount Wilhelm is restricted to a narrow altitu-dinal belt, above the tree limit at 3900 m to about 4300 m. This belt is known in botanical and tourism descriptions of the vegetation and the climb, as the 'dead lichen zone', because the abundant Thamnolia is mistaken for dead lichens. The area consists of a granite bedrock with large boulders, vertical cliffs and horizontal stretches with some soil compaction supporting heathlike dwarf shrub vegetation. This is a small zone where the recently described endemic Sticta alpinotropica [23] occurs on rocks, and the equally endemic Thamnolia juncea [24] is found in the (sub-)alpine grassland. The known world populations of both species amount to only a few square metre. Below the tree limit, the availability of various susbstrates for lichens is much wider, and the lichen diversity in the cloud forest belt is very high. This is the zone where numerous endemic species occur, for example, of the genera Anzia [25] and Menegazzia [26].

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