16.5.3 Adaptation of ‘natural’ ecosystems in island environments
The natural adaptation of small-island ecosystems is considered in very few National Communications. Instead attention is mostly focused on: (1) protecting those ecosystems that are projected to suffer as a consequence of climate change and sea-level rise; and (2) rehabilitating ecosystems degraded or destroyed as a result of socio-economic developments.
One group of natural island environments in low latitudes are the tropical rainforests, savannas and wetlands that occupy the inland, and often upland, catchment areas of the larger, higher and topographically more complex islands, such as Mauritius in the Indian Ocean, the Solomon Islands in the Pacific, and Dominica in the Caribbean. Very little work has been done on the potential impact of climate change on these highly biodiverse systems, or on their adaptive capacity.
On the other hand, the potential impact of global warming and sea-level rise on natural coastal systems, such as coral reefs and mangrove forests, is now reasonably well known. For these ecosystems several possible adaptation measures have been identified. In those coral reefs and mangrove forests that have not been subjected to significant degradation or destruction as a result of human activities, natural or ‘autonomous’ adaptation, which represents the system’s natural adaptive response and is triggered by changes in climatic stimuli, can take place. For instance, some corals may be able to adapt to higher sea surface and air temperatures by hosting more temperature-tolerant symbiotic algae (see Chapter 4, Box 4.4). They can also grow upwards with the rise in sea level, providing that vertical accommodation space is available (Buddemeier et al., 2004). Similarly, mangrove forests can migrate inland, as they did during the Holocene sea-level transgression, providing that there is horizontal accommodation space and they are not constrained by the presence of infrastructure and buildings; i.e., by ‘coastal squeeze’ (Alongi, 2002).
In addition to autonomous adaptation, both restoration and rehabilitation of damaged mangrove and reef ecosystems can be seen as ‘planned’ adaptation mechanisms aimed to increase natural protection against sea-level rise and storms, and to provide resources for coastal communities. In small islands, such projects have usually been community-based and are generally small-scale. In the Pacific islands, successful mangrove rehabilitation projects have been recorded from Kiribati, Northern Mariana Islands, Palau and Tonga, with failed efforts in American Samoa and Papua New Guinea (Gillman et al., 2006). Improved staff training, capacity building, and information sharing between coastal managers is needed for successful mangrove rehabilitation (Lewis, 2005). More ambitious, costly and technical projects include an ecosystem restoration programme in the Seychelles, which aims ultimately to translocate globally threatened coastal birds as well as rehabilitating native coastal woodlands on eleven islands in the country (Henri et al., 2004).