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CENTRES OF PLANT DIVERSITY AND ENDEMISM
VII. Pacific Coast
The Pacific coastal region of tropical South America, sometimes called the trans-Andean region, is a geographically coherent unit even though it is extremely heterogeneous phytogeographically due to its extreme variation in precipitation. It forms a mostly narrow strip along the western side of South America stretching from La Serena just north of 30°S latitude in northern Chile north across the Equator to include the drainage of the Atrato River in Colombia as well as the adjacent Urabá region and the climatically similar wettest part of the Magdalena Valley. Thus the "Pacific Coast" region includes the narrow strip of Caribbean coast that marks the northern limit of Chocó Department, and reaches a northern limit at Cabo Tiburón on the Panama border near 8°45'N.
To the west this region is delimited by the Pacific Ocean and the Panama border. To the east the region is less precisely delimited by the Andean escarpment. The separation of the coastal region from the Andean region is often placed near the 1000 m elevational contour (Gentry 1993a; Dodson and Gentry 1991; Forero and Gentry 1989).
In the geologically and geographically complex region of northern Colombia where the Andean Western and Central cordilleras reach their terminations, vegetation similar to that of the Chocó extends around the northern tips of the two cordilleras into the Magdalena Valley. The wet-forest Nechi area is clearly a part of the Chocó phytogeographically and is logically included in the Pacific coastal region of South America even though the area's rivers drain north into the Caribbean. The moist and wet forests of the central Magdalena Valley are phytogeographically more distinctive and might well be considered to constitute a separate region coordinate with Amazonia or the Mata Atlântica. However, for the purposes of this summary review, the part of the Magdalena Valley between 5°30'-7°30'N is considered under the rubric of the Pacific Coast region.
Ecologically this region runs the gamut from among the wettest to the driest extremes of the neotropics, and the world. In general the northern Chocó region is perhumid, whereas the Sechura and Atacama deserts of Peru and northern Chile are perarid. Coastal Ecuador is transitional, ranging from perhumid rain forest in the north to desert in the south-west on the Santa Elena Peninsula. One of the Earth's wettest places is at Tutunendó in the Colombian Chocó, which receives 11,770 mm of annual precipitation. No rainfall has ever been recorded in parts of northern Chile's Atacama Desert.
In Colombia there is a north-south gradient of lessening precipitation, with the Caribbean coastal region more strongly seasonal. In Ecuador, vegetational zonation depends largely on proximity to the offshore Humboldt Current; precipitation zones are generally parallel to the coast, with the westernmost extension of the country (between Cape San Mateo and the Santa Elena Peninsula) the driest and the Andean foothills the wettest. Due to the strength of the Humboldt Current, coastal Ecuador and the Galápagos Islands are the only places in the world where desert and near-desert conditions reach to the Equator. In Peru and northern Chile the precipitation gradient also decreases from north to south, with the tropical dry forest of the northernmost part of coastal Peru grading into progressively drier desert to the south.
The Chocó pluvial forest is one of the few places in the world with the over 8000 mm of annual rainfall that categorize true tropical rain forest under the widely used Holdridge system of vegetation classification. The perhumid, or pluvial, forest occupies most of the lowland coastal region of Colombia south of 7°N latitude, extending along the base of the Andes across the Ecuador border to a southern terminus near 0°30'N. The Chocó pluvial forest is physiognomically as well as floristically distinctive, being characterized by many features that are normally restricted to mid-elevation cloud forests, including extremely thick coverings of moss and other non-vascular epiphytes on branches and tree trunks and prevalence of hemi-epiphytic climbers rather than free-climbing lianas. There are unusually high densities of trees of small (2.5-10 cm dbh) and medium (10-30 cm dbh) sizes (Gentry 1993b), unusually low densities of large trees, and overall low biomass (FaberLangendoen and Gentry 1991). Holdridge-system wet and moist forests, which are physiognomically (as well as floristically) distinct from pluvial forest, cover most of lowland north-western Colombia north of 7°N, and the north-western part of Ecuador, extending southward as a narrowing strip along the Andean foothills almost to the Peruvian border. Even in the Chocó itself there is a mosaic of wet and pluvial forests, with the low coastal cordilleras generally relatively drier and covered by wet forest. The wet-forest and moist-forest regions have the free-climbing lianas, large emergent trees and high biomass that characterize Amazonian and most other such neotropical forests.
Like Amazonia, the lowland Chocó includes a mosaic of different vegetation types. Several of the most distinctive are swampy, including the best developed and most species-rich mangroves of the neotropics, with at least 15 species of mangroves or mangrove-associated plants, most of which do not occur on the Atlantic coast (Gentry 1982b). In the lower Atrato River drainage of the northern Chocó, there are nearly pure stands of Raphia palm in frequently inundated areas, and in less swampy areas "cativales" with single-species dominance by the legume Prioria copaifera. There are also extensive herbaceous swamps. Scattered along the Pacific coast northward from Esmeraldas, Ecuador are singlespecies dominated freshwater and brackishwater swamp forests respectively dominated by Campnosperma panamensis and Mora megistosperma, in addition to the more continuous mangrove formations.
Not surprisingly considering the heavy rainfall, the soils of most of the Chocó region (see CPD Site SA39) are highly leached and nutrient-poor. Much of the region has typical red-clay lateritic soils but some areas, especially near the base of the Andes and in the floodplains of major rivers, have relatively young less-leached soils. Relatively rich soils are especially prevalent in the southern part of the Ecuadorian Chocó. A peculiar soil type of unusual botanical interest is the white clay that occurs in much of the Bajo Calima region of Colombia's Valle Department and also west of Lita in northern Ecuador. This clay is especially associated with such distinctive Chocó vegetational features as gigantic sclerophyllous leaves and unusually large fruits (Gentry 1986b, 1993b).
The relatively small, anomalously low-latitude, dry-forest area of south-western Ecuador (cf. Kessler 1992) and north-westernmost Peru is very different from the adjacent moist and wet forests in its almost complete loss of leaves during the dry season. The vegetation of this Tumbes region is distinctive among neotropical dry forests in the prevalence of large emergent Bombacaceae trees, which tend to have grotesque growth forms and give the forest a very distinctive aspect. Another peculiarity is the extreme density of herbaceous vines that cover trees and ground alike during the wet season.
The Pacific Coast desert region forms a continuous strip over 3500 km long from near the Ecuador/Peru border at 5°S latitude to La Serena, Chile near 30°S. In the coastal desert regions vegetation is extremely sparse, even entirely lacking over large areas which instead may be covered with drifting sands. Botanically the most interesting part of the coastal desert is the "lomas", a curious archipelagolike formation of mostly ephemeral and geophytic herbs which grow in the condensation zone where winter fogs are intercepted by steep hills adjacent to the coast (see CPD Sites SA42 and SA43). While the lomas have a lush seasonal growth of herbs for several months, for most of the year the plant life disappears entirely, leaving apparently bare desert.
Due to its isolation by the Andes from the rest of lowland South America, the trans-Andean Pacific coastal region is characterized by a high level of endemism, leading to a concomitant need for conservational focus. The flora of the humid Chocó has been very roughly estimated as likely to include 8000 vascular plant species, c. 20% of them strictly endemic (Gentry 1982b). Although there are no endemic families in the wet part of Pacific South America, several genera are endemic and some of them have undergone significant speciation, including Trianaeopiper (17 spp.) (Piperaceae) and Cremosperma (16 spp.) (Gesneriaceae). The flora of coastal Ecuador below 900 m elevation with the Tumbes area of Peru is estimated to consist of c. 6300 vascular plant species, with c. 20% or 1260 species strictly endemic to the region (Dodson and Gentry 1991). The dry-forest portion of coastal Ecuador contributes c. 1000 species to this total, most of them not shared with moist or wet forest, with a similar endemism rate of 19%. Several small genera are endemic to Ecuadorian dry forest, whereas the adjacent moist forest has no endemics.
The predominant families in Chocó are generally those well represented in other parts of the lowland neotropics. For example among the almost 4000 vascular plant species listed for Colombia's Chocó Department by Forero and Gentry (1989), the largest family is Orchidaceae, followed by Rubiaceae, Leguminosae, Melastomataceae, Piperaceae, Compositae, Gesneriaceae, Araceae, Palmae, Bromeliaceae, Solanaceae and Euphorbiaceae. Similarly for the Florula of the Río Palenque Science Center in the Ecuadorian Chocó band (Dodson and Gentry 1978), the largest family is Orchidaceae, followed by ferns, Leguminosae, Araceae, Piperaceae, Compositae, Moraceae, Solanaceae, Gesneriaceae, Gramineae, Rubiaceae, Euphorbiaceae, Melastomataceae and Bromeliaceae. Although somewhat less speciose, predominantly hemi-epiphytic families like Ericaceae and Guttiferae are conspicuously more prevalent in the lowland Chocó than in lowland forests of Amazonia or Central America.
When data for plants of dbh 2.5 cm or more in 0.1-ha samples are compared, Leguminosae, Rubiaceae, Palmae, Annonaceae, Melastomataceae, Sapotaceae and Guttiferae are the predominant families in Chocó pluvial forests (Gentry 1986b). Most noteworthy are the preponderance of Guttiferae, Melastomataceae, Myrtaceae and Bombacaceae as compared to similar samples in Amazonia and Central America. Other families, like Bignoniaceae and Meliaceae, are less prevalent in Chocó pluvial-forest samples than in most other moist lowland neotropical forests. Following this much-replicated sampling technique, the Chocó pluvial forests are the most species-rich in the entire world, although almost equalled by some Upper Amazonian samples.
Certain genera tend to be strikingly species-rich in the Chocó region, although most of them are also among the largest genera elsewhere in the lowland neotropics. The largest genus is Piper, both in Chocó Department and at Río Palenque. Other exceptionally speciose genera in Chocó Department are Psychotria, Miconia, Anthurium, Thelypteris, Peperomia, Maxillaria, Cavendishia, Elaphoglossum, Solanum, Trichomanes, Heliconia, Epidendrum, Columnea, Clidemia and Guzmania (Forero and Gentry 1989). At Río Palenque, Piper is followed by Ficus, Solanum, Peperomia, Philodendron, Pleurothallis, Anthurium, Epidendrum, Maxillaria, Thelypteris and Heliconia (Dodson and Gentry 1978; Gentry 1990a). Most of these species-rich genera are epiphytic, and most of the rest are understorey shrubs and herbs. It has been suggested that such taxa are prone to unusually rapid speciation leading to extreme local endemism, with the Chocó region's foothill cloud forests the epicentre of this phenomenon (Gentry 1986b, 1989; Gentry and Dodson 1987). In the extreme example of the Centinela ridge in central-western Ecuador, a 20-km² area of cloud forest may have supported 90 locally endemic species, about a tenth of the entire flora (Gentry 1986a; Gentry and Dodson 1987; Dodson and Gentry 1991).
The dry forest of coastal Ecuador and adjacent north-western Peru is floristically similar to continentally interior neotropical dry forests, with dominance of Leguminosae trees and Bignoniaceae lianas. Perhaps its most striking floristic feature is the unusual diversity of Bombacaceae (Gentry 1995). In the driest regions, as on Ecuador's Santa Elena Peninsula, Capparidaceae are especially prevalent. This overall region has unusually high endemism for dry forest, with 19% (c. 190) of its species endemic (Dodson and Gentry 1991).
The offshore Galápagos Islands (volume 2, CPD Data Sheet site PO7) constitute essentially a depauperate subset of this flora where only the bird-dispersed and a few wind-dispersed (pogonochore) species of the coastal dry forest arrived, and sometimes speciated. The entire Galápagos native flora includes only c. 541 species of vascular plants (Wiggins and Porter 1971; Porter 1983; Hamann 1995). Endemism is 41.4%, with most of the 224 endemic species being rather obscure herbs (Porter 1983); the dominant dry-forest trees are conspecific with those of the mainland.
Floristically, the coastal desert of Peru and northern Chile has little in common with other equatorial lowlands in South America and more in common with the high Andes. The predominant families are mostly herbaceous or shrubby, and include Compositae, Malvaceae, Cactaceae, Boraginaceae, Cruciferae, Aizoaceae, Portulacaceae, Solanaceae and Umbelliferae (Rundel et al. 1991). The coastal desert area is characterized by very strong local endemism in the lomas formation, with two speciose nearendemic families (Nolanaceae and Malesherbiaceae, both shared with Mediterranean Chile) and genera such as Calceolaria, Palaua, Tiquilia and Nolana showing significant lomas radiations (Rundel et al. 1991). Both diversity and endemism are greater in the lomas of the southern part of the coastal desert, with 62% of southern Peru's lomas flora endemic (Müller 1985). There is also a sharp floristic break near the Peru/Chile border with only 7% of the region's species occurring on both sides of this climatic barrier (Rundel et al. 1991). Although the individual lomas have relatively small floras usually of less than 100 species (with 230 in the richest, the Paposo area), there is such a strong degree of local endemism that the coastal desert contributes an estimated additional 1000 species to the Pacific coast total (Rundel et al. 1991).
The Chocó region has a very large complement of useful plants and presumably a very real potential for conservation via extractive reserves and other sustainable uses of forest products. Moreover, many of the useful species of this region appear to be locally endemic, and a very different set of genera and families are of economic importance in the coastal Pacific wet forests than in Amazonia or Central America. Included among the region's useful plants are many fruits such as the wildly popular local delicacy "borojo" (Borojoa patinoi). RomeroCastañeda (1985) lists 42 Chocó fruit species that are edible, including such otherwise rarely consumed genera as Montrichardia, Aechmea, Crataeva, Leonia, Malvaviscus, Patinoa, Maripa and Pentagonia. Several of the unusually large fruits that characterize Chocó species are consumed, including Orbignya cuatrecasana and Compsoneura atopa. Another peculiarity of the consumption is that various fruits are consumed as a source of starch rather than for their sweet sugary taste (Gentry 1992c). A surprising number of the edible species are recently scientifically described or have yet to be described (Gentry 1992c).
The region is rich in plants used for fibres, including many palms (Bernal 1992) and aroids (e.g. Heteropsis, Philodendron - Gentry 1992c); the fibres of Carludovica palmata (Cyclanthaceae) form the basis of Ecuador's "Panama hat" industry (Miller 1986). There are also plants with horticultural potential. A good example is Anthurium andreanum, among the world's most widely cultivated aroids, which is endemic to a small region of western Colombia and north-western Ecuador; its collection was an important source of income for the Quaiquer Amerindians until local populations were decimated. A major effort is currently underway to revitalize the harvest of "tagua" (Phytelephas), formerly much used for buttons and as an ivory substitute, as a conservation-motivated sustainable extractive industry (Calero-H. 1992; Bernal 1992; Ziffer 1992). Canning of palm hearts (from Euterpe oleracea) is a significant local industry with six factories along the Colombian coast (Bernal 1992). In coastal Peru, the manufacture of "algarrobina" from Prosopis fruits to flavour drinks forms an important local industry.
The Pacific coastal region's abundance of tree species includes many species that have been harvested for timber. Again a very different taxonomic complement is exploited locally than elsewhere in the neotropics. Among the most important timber trees are several of the species that form single-species dominated stands including Prioria copaifera ("cativo") in the north, which is rapidly disappearing; Campnosperma panamensis ("sajo"), which is the single most important central Chocó timber species, accounting for 16% of the regional timber production in 1982; and Mora megistosperma ("nato"), with 280 km² harvested by 1982 (CVC 1983). In the high-rainfall part of central Chocó, Goupia and various Humiriaceae are the major timber species. The coastal Ecuador wet forest has lost its timber industry along with its trees; the formerly most important timber tree of the region, the rather recently described endemic Caryodaphnopsis theobromifolia, has been reduced to a few trees in the 1-km² Río Palenque reserve. The extremely hard wood of Tabebuia chrysantha ("guayacán") is the most exploited timber of the coastal Ecuador dry forest; as it has disappeared, the handicraft industry formerly dependent on it has turned to painting inferior woods so as to create imitations of the prized species.
The conservation status of the Pacific coastal region of South America is generally grim. Both the Colombian Chocó and coastal Ecuador were singled out by Myers (1988) as two of the world's 15 evolutionary hot spots in need of special conservation focus. The lomas formations have also been heavily impacted by human use, including pollution from mining, overgrazing during the winter growing season and even construction of new towns, but fewer species may be at risk (Ferreyra 1977).
Overall, 96% of the forests of coastal Ecuador have been destroyed, in an area of high regional and local endemism; only 1% of the coastal dry forest remains. Isolated cloud-forested outlying ridges apparently have significant complements of extremely local endemics. When deforestation of one of them was completed, on the 600 m elevation Centinela ridge south of Santo Domingo de los Colorados, perhaps 90 species of plants went extinct (Gentry 1986a; Dodson and Gentry 1991), one of the most massive local extinctions from tropical deforestation to date. The concept of "Centinelan extinctions" has even entered the conservation literature (Wilson 1992).
While three-quarters of the Colombian Chocó forest remains intact, large areas in the north and south are completely deforested, as is the Bajo Calima area. If the suspected pattern of high local endemism prevails in floristically poorly known Chocó, similar extinctions may be anticipated there as well, if deforestation continues unabated. Also, the Magdalena Valley has significant endemism and has been mostly deforested.
As in many other parts of the tropics, deforestation is the major contributor to the loss of biodiversity in the Pacific coastal region of South America. Western Ecuador is a particularly poignant example of this change (Parker and Carr 1992). Even though the rate of population increase dropped from 3.2% per year a few years ago to 2.4% by 1992 (World Population Data Sheet), Ecuador's population continues to grow alarmingly. Aggressive road-building and agricultural settlement programmes have accelerated forest loss as has a sociopolitical climate where privately owned forested lands are considered "unused" and susceptible to expropriation, either officially or extraofficially via squatters (Dodson and Gentry 1991). Unlike many tropical areas, the relatively rich soils of much of western Ecuador make agriculture sustainable as well as profitable, increasing the pressures on forest remnants.
The same processes that have already led to the devastation of western Ecuador's forests are currently in operation in western Colombia, where they are aggravated by environmental impact from large-scale commercial operations including oil-palm plantations (especially in Nariño), banana plantations (Urabá area), paper-pulp production (mostly in lowland Valle) and timbering (especially in northern Chocó). According to Myers (1988), 28% of the Colombian Chocó has already been deforested.
Over-exploitation of natural resources is also a problem. For example, mangroves are extensively harvested in the Buenaventura area for construction timber and tannins - virtually the entire 2420 km² of mangrove forest having been exploited at least once; 21,292 m³ per year of mangrove wood were being cut by 1982 (CVC 1983). Worse, in Ecuador mangroves are being replaced entirely by shrimp farming operations. The once extensive "cativales" of northern Chocó have been decimated by timbering operations as has much of the Atrato region's upland forest. By 1982, 23% of the Pacific coast forests of Colombia had been harvested for timber, including well over 5741 km² in the southern and central coastal region alone (CVC 1983). Most of the northern Chocó has been assigned to timber concessions.
Several large conservation units have been designated in this region (see CPD Data Sheets), with a total of c. 11,000 km² officially protected in the Pacific coastal lowlands. About half of the total is in the wet northern region, including four lowland National Parks in Colombia plus the lowland part (to 100 m) of Paramillo NNP (which has 4600 km²) in Colombia's Córdoba and Antioquia departments and the Cotacachi-Cayapas/Awá reserve area in Ecuador. There is no conservation unit in the Magdalena Valley. Two large dry-forest National Parks total c. 1300 km² - Machalilla in Ecuador and Cerros de Amotape in northern Peru. There are two national sanctuaries in the Peruvian Desert region, Lomas de Lachay and Paracas, totalling 360 km² - however 60% is marine. In addition most land in the Galápagos Islands is designated as a National Park. Thus the remaining natural vegetation of the Pacific coastal region, except the Magdalena Valley, might seem to be well protected.
However, attempts at direct conservation via National Parks have been notably ineffective in much of the Pacific Coast region of South America. For example the only legally protected dry forest in coastal Ecuador is Machalilla NP, but as much as 75% of its surface area remains effectively in private hands and the forest has been largely decimated since the park was established (in 1979) (contrary to IUCN 1982 - see Arriaga 1987; Parker and Carr 1992). Cerros de Amotape NP in Tumbes, Peru, still effectively protects some dry forest, but is seriously threatened by livestock browsing and fire. The large Cotacachi-Cayapas Ecological Reserve in northern Ecuador, which spans what was originally an intact ecological gradient from the high Andes to the coastal lowlands, is being seriously encroached along its boundaries (Parker and Carr 1992). Most of the lowland part of Paramillo NNP at the north tip of the Western Cordillera in Colombia has been clear-cut for cattle pasture, apparently since the park was established (in 1977). Most of Los Katíos NNP in the Urabá area of Chocó near the Panama border was deforested while the park was in the process of being established (in 1973). It is obvious that a much greater effort is needed if such reserves are to be effective.
A number of novel conservation strategies seem to have been more effective in conservation than the underfunded and understaffed National Parks. In Ecuador the best preserved dry forest is the Arenillas Reserve (200 km²) protected by the military as a buffer along the Peru border. In Colombia watershed protection has been exemplary by the Corporación Valle del Cauca (CVC) for its electricity-generating system on the Anchicaya River. Small private reserves like La Planada in Colombia and in Ecuador Río Palenque and the Universidad de Guayaquil's Jauneche are playing an important conservation role, which needs to be expanded.
Perhaps most significant of all, there is growing appreciation of the significance of conservation, with local sustainable-use initiatives, generally supported by NGOs (non-governmental organizations), seen in part as a mechanism for protecting forest populations of people and their cultures from being overrun by outsiders from adjacent montane areas. Recently established indigenous reserves that occupy a significant part of the still-forested Chocó will hopefully play a similar role. Even some of the large companies notorious for forest exploitation have begun to see the importance of forest conservation, to the extent of setting aside and protecting reserves on their own initiatives. Ecotourism, currently almost non-existent in this region, is perceived as a potential new source of income that could be compatible with conservation of biodiversity and local lifestyles as well. The connection between widespread deforestation and energy rationing due to lack of hydroelectric power from empty or silted-up reservoirs has become widely recognized.
Centres of Plant Diversity and Endemism
SA39. Colombian Pacific Coast region (Chocó)
SA40. Ecuadorian Pacific Coast mesic forests
SA41. Cerros de Amotape National Park region
SA42. Lomas formations
SA43. Lomas formations of the Atacama Desert
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