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| Vegetation of the Galapagos | |
 Vegetation Zones in the Galapagos |
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Vegetation
Although located on the equator the Galapagos Island lie within the Pacific Dry Zone, an area that receives very little annual rainfall and the vegetation of the Islands is therefore unusually arid. Lowland areas are thus dominated by desert or semi-desert like conditions. Young and fresh lava flows are extensive and almost bare of vegetation. Lava cactus and few lichens are often represent the only vegetation in these areas. Older lava flows become covered by open dry forest dominated by Palo Santo (Bursera graveolens). Small and flat islands are dominated by this dry vegetation. However, larger islands typically reach considerable altitudes and in the highlands, were rainfall is more common, the vegetation transitions into humid tropical cloud forest, scrubland and a fern-sedge dominated vegetation.
Vegetation Zones
Traditionally seven distinct vegetation zones have been distinguished for the Galapagos Islands: (1) coastal zone, (2) dry zone, (3) transition zone, (4) brown zone, (5) Scalesia-zone, and (6) fern-sedge zone. This classification was first introduced by Wiggins & Porter (1971) in their Flora of Galapagos. Their system is not with out problem because many of these zones were based on the vegetation of the main, central island Santa Cruz, and several plants typically for this island are not present on other islands. Also, unlike Santa Cruz Islands, a few of the highest volcanoes in the archipelago reach far beyond the cloud level and their peaks are characterized by an arid vegetation not present in this traditional classification.
The traditional system thus represents a mixture of altitude vegetation zones and plant communities dominated by particular plants like the forests of the endemic Scalesia pedunculata or the Miconia-scrubland of Santa Cruz. These are both more aptly referred to as vegetation types because they do not generally represent a vegetation characteristic for all Galapagos islands.
On the south exposed sides of the islands, where clouds drift against the higher slopes. generally five altitudinal Vegetation Zones can be distinguished throughout the Galapagos. Northern slopes are generally drier, and here vegetation zones are thus often compressed. Generally the humid vegetation is less well represented or even lack entirely on these slopes.
Coastal Zone
The Coastal Zone is a narrow belt in immediate vicinity to the sea and it thus occurs on all Galapagos islands. Generally most common are bare lava flows, or lava covered with coastal scrub like Scutia ssp. and Ceyptocarpus pyriformis. Sheltered, old lava flows where dewfall is common are often covered abundantly with lichens. In lagoons and flat, sheltered areas where fine sediment accumulates mangroves represent the dominant vegetation along the coast. Sandy beaches are generally less common.
Dry Zone
On exposed, young lava flows the endemic lava cactus is often the only sign of plant life that can resist this extreme conditions, on these hot and dry, barely weathered rocks even lichens are rarely found. The most common tree throughout the dry zone of the Galapagos is Palo Santo, Bursera graveolens. It is a relatively low tree and typically forms light and open forests, often mixed with tree-like Opuntia species, or columnar cacti.
Transition Zone
In the transition zone stands of Bursera trees become much denser, and Catclaw Zanthoxyolon fagara becomes the most characteristic and often dominant tree. Very characteristic for this zone is the abundance of pale yellowish green fruticose lichens that abundantly cover branches and twigs as long beards, Ramalina usnea, Ramalina anceps, and Usnea longissima among the most common species.
Humid Zone
The humid zone is very diverse and Wiggins & Porter (1971) therefore divided this zone. Many forests are dominated by various liverwort species of the genus Frullania that form thick carpets on tree trunks, branches, and twigs. Epiphytic liverwort carpets are, however, very common throughout the humid zone and not necessarily restricted to "brown zone". In fact, the Scalesia forests of Santa Cruz are abundantly covered in Frullania species.
High Altitude Dry Zone
This zone only occurs on the highest Galapagos volcanoes, Fernandina, Cerro Azúl, and Vólcan Darwin. It is confined to the peaks that reach beyond the cloud layer, and thus reach from the humid zone into an area that again receives very little rainfall.
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