San Félix-San Ambrosio Islands temperate forests
This group of relatively small oceanic islands, known as the Islas Desventuradas, is located approximately 850 kilometers (km) off the coast of Chile. Both islands are of volcanic origin, and both the terrestrial and marine flora and fauna are of great scientific interest, though we know little about them. San Ambrosio rises from the sea as sheer cliffs on almost all sides, is 4 km long by 850 meters (m) wide, and primarily basaltic. San Felix is slightly smaller and has two small peaks, reaching 193 meters (m), which are denuded by high winds. The vegetation is a miniature mosaic of matorral, barren rock, various size trees, and shrubs mixed with ferns and perennial herbs.
Location and General Description
The Desventuradas archipelago is formed by the islands of San Félix (26°17’SL-80°05’ WL) and San Ambrosio (26°20 LS-79°58’ WL), and is part of the ocean territory of Chile. It lies some 850 km west of continental Chile and some 780 km north of the Juan Fernández Archipelago. The surface area of the first is 2.5 km2 and the surface area of the latter is 2.4 km2; they are separated by some 20 km.
San Félix is a triangular shaped island with a rather flat surface at the NW end of which is found Amarillo hill (193 m high); on the opposite end, separated by a straight, we find the small island of González (166 m). All along the coast, there is intense erosion by the sea. The island has a volcanic origin and its flatland consists of laminar strata of olivinic basaltic lavas; it is probably the upper structure of a recently active volcano as dating of the lava yields an age of some 100,000 years.
San Ambrosio is a massif the upper portion of which includes a plain rising to some 254 m with altitude decreasing to the north until reaching 100 m. The plain is lined by small ravines. There are no beaches and the cliffs fall directly to the sea, making access difficult. Like San Félix, it is also of volcanic origin and lava flows have been measured from 2.86+0.14 millions ago, providing indications of the age of the archipelago. In addition, both islands are part of the Pascua volcanic chain.
Only the climatic characteristics of San Félix are known. The climate is Mediterranean, moist, warm and oceanic. Maximum temperature is 22.5°C, minimum temperature is 14.3°C and the average is 17.8°C. Rainfall is 94.8 millimeters (mm) occurring primarily in winter (May-August). According to de Martonne’s index, there are 3 arid months, 2 semi-arid months and 7 wet months. The topography and geographic orientation of San Ambrosio island favor the retention of fogs, thus providing a more favorable microclimate for the development of vegetation.
There are no permanent sources of fresh water on the islands and it is probable that there are only temporary waterways associated with rains.
With respect to vegetation, there are only descriptive works written during sporadic and brief visits.
The physiognomy and vegetation of San Félix island reflect arid conditions and thus the island is a schlerophyllous, low scrubland, where cover does not exceed 25% and bushes 20-30centimeters (cm) high bushes with cushions predominate.
Woody plants show three ecological strategies:
- deciduous woody in summer: Thamnoseris lacerata var. lobata (Asteraceae-Cichoroideae), the only tree on the island.
- bushy woody, evergreen, microphyllous (small leafed): Frankenia vidalii (Frankeniaceae) and Atriplex chapinii (Chenopodiaceae).
- woody, bushy, with succulent leaves: Suaeda nesophila (Chenopodiaceae) and Maireana brevifolia (Chenopodiaceae).
Based on soil characteristics and human influence, the same authors recognize four types of environments. The most frequent plants are Eragrostis peruviana (Poaceae) and the endemic plants Atriplex chapinii, Thamnoseris lacerata and Cristaria insularis (Malvaceae). The unit with the highest number of species is the area most affected by man. However, close to 50% of these are allochthonous species (i.e., Chenopodium murale, Cotula coronopifolia and Sonchus asper).
The fauna on this island is scarce and there is information only on the marine and land birds that live there. There are no records of other vertebrates.
With respect to marine birds, the nesting of boobies, Sula dactylatra and Sula leucogaster, has been recorded. The presence and reproduction of Sula nebouxii are also possible. This could explain their abundance in the ocean waters of northern Chile, which is probably the species’ southernmost nesting site.
There are also records of the nesting of fardelas, Pterodroma neglecta and Pterodroma cooki. At least three species of terns probably nest on this island, namely Sterna fuscata, Anous stolidus and Procelsterna cerulea. The size of their reproductive populations is unknown.
The most conspicuous species on San Ambrosio island are Thamnoseris lacerata and Sanctambrosia manicata (Caryophyllaceae), among woody species, and among grass species, Eragrostis peruviana and Eragrostis kuschelii (Poaceae), annuals that may reach as high as 50 cm. Two communities are distinguished on the upper plain: very dense Thamnoseris-Atriplex and less dense Atriplex, Lycapsus tenuifolius (Asteraceae) and Eragrostis spp. Additional species include the following: Thamnoseris-Sanctambrosia manicata (Caryophyllaceae); Nesocaryum stylosum (Boraginaceae)-Frankenia vidalii and Solanum brachyantherum (Solanaceae)-Lycapsus tenuifolius. On the cliffs that benefit more from the accumulation of moisture, the vegetation is denser and consists of bushes such as Atriplex spp., Suaeda nesophila, Frankenia vidalii and Nesocaryum stylosum and grasses such as Sicyos baderoa var. ambrosianus (Cucurbitaceae).
Compared to San Félix, San Ambrosio island generally has greater plant cover and in sectors that benefit from fog, there are individual examples of Thamnoseris lacerata up to 5 m high. Greater plant cover is also associated with the presence of more developed soils.
The fauna of this island is likely to be similar to that on San Félix island, with records of nesting by fardelas Pterodroma neglecta and Pterodroma cooki, with colonies that are probably more numerous than on San Félix. There are also nests of species of the terns, Sterna fuscata, Anous stolidus and Procelsterna cerulea as well as a small population of the cernícalo, Falco sparverius fernandensis, the only land bird of the archipelago.
Varies species of marine birds have been recorded on the sea next to these islands which are probably the winter location of species that reproduce in Antarctica, such as the petrel gigante, Macronectes giganteus and the petrel moteado, Daption capense.
The Desventuradas Islands Archipelago is a relatively recent volcanic formation and its principal environmental characteristics at present are a significant degree of isolation (more than 700 km away from any point) and a Mediterranean climate with precipitation concentrated in lower temperature months. Although the climate is oceanic it has a significant degree of aridity due to limited rainfall (less than 100 mm, a 10-year average). Another important characteristic is the islands’ limited area, about 2.5 km2 on each island, limiting the development of their biota.
The vascular flora of the Islas Desventuradas consists of 33 species and two varieties. Twenty-five taxons are native (68%) and 11 are allochthonous (32 %). This figure has been determined on the basis of expeditions beginning in 1869, the results of which have been published by many naturalists. One of the most interesting aspects of the explorations of the islands, from the point of view of the flora, is that since 1869 the information relating to the flora has been provided by only two botanists. The remaining plant collections have been compiled by other naturalists (entomologists, ornithologists, marine biologists) and, frequently by personnel on Chilean Navy ships.
The principal aspect in the analysis of vascular flora is the high degree of endemism. In this regard, if only native species are considered, the archipelago’s endemic species reach 60.8% (14). Considering varieties and endemic forms (4), this amounts to 18 endemic taxons, 72 % of the native taxons. On San Ambrosio, 45% of the taxons are endemic to the island. On San Félix, this percentage falls to 10.5%. In terms of wealth, San Ambrosio has 24 taxons (22 species, 13.6% of them allochthonous) and San Félix has 20 taxons (19 species, 42% of them allochthonous). If we consider only native species, the similarity percentage (Söhrensen) of the flora on the two islands is 64 %; 8 taxons are found on both islands, 15 are found only on San Ambrosio (including 11 taxons endemic to this island and two allochthonous species) and 11 taxons grow only on San Félix and of these two are endemic to this island and 7 are allochthonous.
In this regard, extremely important from the standpoint of preserving biodiversity are the four endemic monotypic genera: Lycapsus (Asteraceae-Heliantheae), present on both islands, Nesocaryum (Boraginaceae, related to Heliotropium), endemic to San Ambrosio, Sanctambrosia (Caryophyllaceae-Paronychioideae) a bush endemic to San Ambrosio and Thamnoseris (Asteraceae-Cichoroideae), a pachycaul tree related to Dendroseris, a genus endemic to the Juan Fernández Archipelago, present on both islands but on San Félix as T. lacerata, lobata form.
In terms of phytogeographic affinities, species that are neither endemic nor auchthonous, an important group of species, have a geographic distribution that includes the Atacama Desert coast of Peru and Chile. These include Solanum brachyantherum, Eragrostis peruviana and Tetragonia macrocarpa. To be noted, however, is the absence of Nolana (Solanaceae), one of the most characteristic genera of the Atacama Desert flora. One species, Tetragonia tetragonioides, is widely distribution on the coast of the southern hemisphere and Spergularia confertiflora, the presence of which is considered doubtful for islands, is present on Juan Fernández. One of the most surprising phenomena is the presence of Maireana brevifolia, an Australian species, known only on San Félix. The affinities of the taxons endemic to the islands are found in northern Chile and southern Peru. Although to date there is no satisfactory phytogeographic classification for the flora of the islands, the data presented indicate that this is a very unique area, with few relationships with nearby flora, and the greatest affinity would be with the flora of the Atacama Desert.
The islands are interesting for the study of the colonization and evolution of plant species. However, there are no studies along these lines.
From the standpoint of environmental conservation, San Ambrosio is better preserved than San Félix, because this latter island has a permanent human presence. This has meant construction of infrastructure and the introduction of exotic crops. An indicator of the degradation of the flora is the allochthonous species that have established themselves in the wild, already accounting for 42%. On San Ambrosio, only the presence of fisherman is recorded, but this is neither permanent nor seasonal. Apparently, from the point of view of flora, environments are well preserved and to date there are three allochthonous species that have established themselves in the wild (13 %).
There are no studies on the degree of threat to any of the island’s species of vascular flora. It would be desirable at a minimum to begin studies on the four endemic genera.
Vertebrates inhabiting both islands are exclusively limited to birds. Ten species of marine birds and one land bird species make their nests on or visit the islands. Eight species live on the islands, including Falco sparverius fernandesianus, found only on San Ambrosio. Sula nebouxii might have its distribution boundary on these islands, which would bring the number of species to eleven.
The islands’ marine birds are characteristic of subtropical waters; evidence of this are Sula dactylatra and Sterna fuscata, birds that nest at any time of year, indicating a tropical type of reproductive behavior.
Important for the preservation of species is the presence on both islands of the fardelas, Pterodroma neglecta and Pterodroma cooki. The latter is considered an endangered species and these islands represent two of the three places in the world where the species reproduces.
The raptor, Falco sparverius fernandensis, the cernícalo, is represented in San Ambrosio by a subspecies lives on this island as well as on the Juan Fernández Archipelago.
There is no detailed information regarding which birds nest on San Ambrosio and which birds nest on San Félix.
From the standpoint of their relations with other ocean islands of Chile, the ornithological fauna of the Islas Desventuradas includes some species that are also present on the Juan Fernández Archipelago (7), Easter Island (4) and Sala and Gómez (3). Only Falco sparverius appears both on these islands and continental Chile, although on the islands it is represented by an oceanic subspecies.
The Islas Desventuradas and the surrounding seas are not currently under type of protection provided by the government of Chile. The islands also have scientific and tourism potential and unsuccessful requests have been made to include at least San Ambrosio island in Chile’s National System of Protected Wildlife Areas.
Types and Severity of Threats
On San Félix island there is the permanent presence of a detachment of the Chilean Navy. The effects on this on the biodiversity of these islands are unknown, although the construction of any infrastructure represents a significant reduction in habitat, already limited by the size of the island.
- The human presence is permanent on San Félix while on San Ambrosio it is occasional (lobstermen). The principal threat associated with human presence has been the introduction of many allochthonous species of plants and animals. In terms of flora, the most affected is San Félix island, with 42% of allochthonous plants. Two new allochthonous species were recently found, Amaranthus reflexus and Mesenbrianthemum cristallinum. The latter is an annual, succulent grass of South African origin that on Chañaral island (Teillier, personal observation) and continental Chile has become a very aggressive invader in arid, altered environments. In terms of animals, it is indicated that domestic cats and dogs on San Félixthat prey on bird life. In addition, recent observations indicate the arrival of the mouse, Mus musculus. There is no recent information on San Ambrosio island, but the presence of synanthropic goats and rodents. Some activities associated with the presence of humans bring with them significant noise levels, but there is no evaluation of their effect on local bird populations.
- Agriculture: Incipient agriculture is practiced on San Félix island, representing a source of potential invaders and reducing the habitat of native species.
Justification of Ecoregion Delineation
The Desventuradas islands were distinguished from other ecoregions by the great distance of the islands from the mainland and from other islands, and by the presence of endemic species and breeding/nesting seabird colonies.
Additional Information on this Ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
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