The phrase “sky islands” was initially coined by Weldon Heald in his publication describing the mountains of southeastern Arizona; remote montane forests or woodland surrounded by an expanse of desert. Sky islands form when the uppermost reaches of ridges become isolated physically from each other and ecologically from surrounding lowland environments.
They are similar to oceanic islands in the dramatic biodiversity in species and ecosystem processes among isolated high elevation systems, and between these systems and adjacent lowlands. For example, the ‘original’ sky islands in Arizona support dense coniferous forests, rich aquatic environments, and alpine tundra isolated within a ‘sea’ of some of the most arid desert environments on earth. When these isolates occur in tropical montane areas, they result in high levels of endemism with numerous species restricted to small expanses.
The Australasian archipelago, which includes the Solomon Islands, is biologically very diverse due to a complex geological and biogeographic history. An exceptional feature in this archipelago of almost a thousand islands is its chain of larger islands characterized by high mountain interiors and high, dormant volcanoes encircled by tropical lowland rainforest or ocean. These insular mountain ecosystems act as species pumps and continue to be understudied, even though Australasia, for instance, represents some of the most spectacular tropical alpine habitats on earth.
Dramatic developmental changes occur in species on remote islands. Since the observations made by Darwin on the Galapagos, islands have long been recognized as ‘laboratories’ for the study of evolution. The limited scale, remoteness, and sharp boundaries of islands produce exceptional selective pressures, frequently resulting in spectacular effects. For example, gigantism amongst tree rats on Bougainville and Choiseul, colourful plumages on birds, etc.
SOLOMON ISLAND SKY ISLANDS
As a result of the ‘Massenerhebung’ effect, where forest zones are compressed on small islands (compared to larger islands like New Guinea), montane forests begin appearing in lower elevations. The montane forests that occur on small isolated mountains and outlying ridges of islands like those of Gatokae, Guadalcanal, Kolombangara, Malaita, or Vangunu, are compressed and the stunted elfin woodland of upper rain forests occur as low as 690m. Such is the mossy vegetation on the forested crater rim of Vangunu Island, on Mt Gallego on Guadalcanal, and north – east Makira in the Pagato area.
Based on shuttle radar topography mission data, a map of sky islands for Solomon Islands above 690 meters elevation shows a total land area of 187,750 hectares occurring on thirteen islands. This area represents isolated and unique habitats that in turn drive speciation processes amongst wildlife or any organisms for that matter that occupy these upland niche spaces.
The Guadalcanal highlands stand out as one of the last remaining unknown and untouched sky island areas in the Pacific. This isolated and inaccessible place is a true biodiversity hotspot, housing many species still unknown to science. Not only is this area of natural importance but it is also an area of high cultural value, a factor that has helped in its preservation.
Amongst the highest peaks in the insular tropical Pacific, Mt Popomaneseu (2355 meters ) on Guadalcanal, and Mt Veve (1770 meters) on Kolombangara contain over 50,000 hectares. The upper plateau is characterized as montane cloud forest (>1000 m), with bogs and grass areas.
The topmost ridges are often covered in fog or rain clouds, and water here drains into adjacent primary watersheds forming some of Solomon Islands largest river systems. The stunted forests here are habitat for many plant species such as orchids and vertebrates like the tiny Cornufer (Batrachylodes) frogs.
Scientifically, very little is known of these upland areas. What we know however is that a wide variety of restricted range organisms make their home in these remotes forests. On Guadalcanal this includes the King rat (Uromys rex), the Guadalcanal honeyeater (Guadalcanal inexpectata), and the poorly known Mustached kingfisher (Actinoides bougainvillei), arguably the rarest kingfisher on earth, with no verified observations of the bird since its description earlier in the last century. On Kolombangara, there are undescribed giant rats, unknown species of frogs, and numerous species of mosses and liverworts.
CONSERVATION OF INSULAR SKY ISLANDS
Increasingly, sky island ecosystems are being cleared, fragmented and disturbed at rates which may exceed those of the better-publicized lowland tropical rain forests. Even protected areas on tropical mountains undergo greater deforestation than their lower altitudes.
Insular sky islands are important for a number of reasons. They have a hydrologic importance and provide watershed protection functions. They also have a great biological diversity value and exhibit high levels of plant and animal endemism. Most organisms that inhabit sky island ecosystems normally do not occur anywhere else on earth, but a particular habitat. For example, the Kolombangara leaf warbler is only found in high montane forests of Kolombangara Island, and nowhere else on nearby islands, or on earth.
Hence sky islands are also exceedingly fragile systems, where disturbances and climate shifts can lead to irreversible transformation of the critical ecological state of bamboo, cloud forest, and alpine heath ecosystems which are characteristic of sky island ecosystems.
To many cultures, mountains are sacred areas that hold heritage value. Since time immemorial, indigenous cultures such as those of the Pacific Coastal Mountains of western North America, have journeyed from permanent settlements in lowland regions to upland sites to harvest and process plant resources – food, materials and medicines. As well as to hunt and fish, and undertake spiritual activities.
Likewise, in many Oceanic cultures mountains are revered. Tangible cultural heritage values can be measured by evidence of cemeteries, historic pilgrimage routes or paths, ovoos (stone piles), refuges, repositories, shrines, vistas and viewpoints, all of which are associated with any sky island in Solomon Islands. The mountains or sky islands on any major island in the Solomon Islands are an important spiritual place.
Expeditions and studies that intensively survey plant and animal communities in the cloud forests and heaths of Solomon Islands sky islands, continue to unravel new discoveries among plants, birds, reptiles, amphibians, mammals, fish and invertebrates.
Although most expeditions here are scientific in their framing, the objectives are to go beyond science. Journeys into the least known biodiversity hotspots of sky islands are also meant to serve as a symbol of the enduring relationship between indigenous people and these sacred mountains.
Raising awareness of the ecological and cultural importance of sky islands will hopefully contribute to their conservation, so our children’s children can continue to enjoy and benefit from the richness of sky islands.
Story and photography by Patrick Pikacha.