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CENTRES OF PLANT DIVERSITY AND ENDEMISM.
I. Caribbean Region (of South America)
The coastal area of northern Colombia and Venezuela is phytogeographically distinct from the rest of South America and more closely related floristically to Central America and the West Indies. The region includes the Cordillera de la Costa of Venezuela as well as the Llanos savanna grasslands, and the strongly seasonal lowland forests bordering the Caribbean coast. The latter includes a small area of dry thorn scrub in the most northern, driest part of the region on the Guajira Peninsula. The area north of the Orinoco River is open savanna interrupted by gallery forests along the major rivers, and is phytogeographically completely different from adjacent Amazonia. The region is delimited to the south by the Orinoco and its major Colombian tributary the Guaviare, and to the west the limit is the 500 m contour of the Andean Cordillera Oriental. The division between the Andes proper and the Coastal Cordillera is not the Colombia/Venezuela border, but near the Yaracuy Depression; thus the uplands of Táchira, Mérida and Trujillo states of Venezuela are included in the Andean region.
Around the northern margins of the Central Andean and Western Andean cordilleras in Colombia, delimitation of the Caribbean region from the Andes and from the western Colombian Chocó region is more complicated. West of the Sinu River and especially in the Atrato Delta region, the Caribbean coastal area is much less seasonal and phytogeographically might more appropriately be included in the Chocó region. The vegetation of much of the central Magdalena Valley of Colombia is also humid moist and wet forest and has phytogeographical affinities with both the Chocó and Amazonia. There is a significant endemic element in the moist part of the Magdalena, which also includes a large swampy zone with several distinctive floristic elements. However the upper Magdalena Valley is strongly seasonal dry forest and phytogeographically a part of the Caribbean coastal region. The wet-forest part of the Magdalena Valley and the adjacent Nechi area are referred to the Pacific Coast region, whereas the bulk of the Magdalena Valley up to 1000 m in elevation and south to Neiva at 3°N latitude is included in the Caribbean region. The narrower dry interior Cauca Valley can similarly be referred to the Caribbean region.
The Caribbean region of South America as a whole has perhaps 6000 angiosperm species and a relatively low regional endemism estimated at 24% (Gentry 1982a). This is by far the lowest level of regional endemism of the neotropical phytogeographic regions recognized by Gentry (1982a). The lowland forests of the Caribbean region are highly seasonal and not very diverse botanically. Similarly the Llanos have very little endemism, unlike their physiognomic counterpart the cerrado.
The Cordillera de la Costa, geologically not a part of the Andes, is geographically in essence an Andean outlier, but floristically may be more similar to Central America. There are also some disjunctions with Guayana and Amazonia (Steyermark 1982). This mountainous region has a more diversified flora and a significant complement of endemic species, estimated at 10%. Endemism and species richness are both concentrated in the wet montane areas. A hint of the floristic richness comes from the Florula of Cerro Avila above Caracas (Steyermark and Huber 1978), which includes 1892 species of vascular plants. This is the most species contained in any similar Florula, but the data are not strictly comparable, since the Avila Florula covers several different vegetation zones.
Most of the flora of the region is shared with that of Central America, and there seems little doubt that there must once have been more or direct connections between the seasonally dry forests of coastal Colombia and Venezuela and those of western Central America. There are also several small areas on limestone hills near the coast (e.g. Coloso, Colombia) which have a few taxa of distinctly Caribbean affinities, such as Buxus.
The indigenous peoples of the dry Caribbean coastal region eat the fruits of a variety of local species including Bactris gasipaes, Chrysobalanus icaco, Geoffroea and Acrocomia. In moister regions Gustavia superba is a familiar native species with an edible fruit. In more upland forests of the Sierra Nevada de Santa Marta, the wild-harvested fruits of Metteniusa edulis ("cantyi") and Pouteria arguacoensium ("manzana") are dietary staples (Cuadros 1990). The coastal region also has many tree species with useful wood, including both widespread taxa like Cordia alliodora, Aspidosperma polyneuron, Tabebuia rosea, and endemic species like Tabebuia billbergii - the national tree of Venezuela (Cuadros 1990; Gentry 1992a).
The coastal areas of northern Colombia and Venezuela have been intensively occupied, following the arrival of the first European colonizers in the early 16th century. They are now very densely populated, and have some of the largest cities of the region (Caracas, Maracaibo, Cartagena). The main impact on the flora and vegetation has been caused by shifting cultivation and large-scale deforestations for agricultural and urban purposes. In general the entire region is heavily affected, especially at lower elevations, but there are still some remnants of montane cloud forests protected in several National Parks and Natural Monuments.
The survival of representative and viable samples of arid vegetation in north-eastern Colombia and northern Venezuela is being heavily affected by large-scale conversion into agricultural lands, selective timber extraction - especially boles of certain arborescent cacti for furniture, and browsing by goats. Dry forests are threatened by logging and deforestation for pasture and agricultural lands.
Most of this region has been devastated by human activity. The situation is especially critical in northern Colombia, where the largest patches of remnant natural vegetation include rather few km. The shining exception is the dry forest (not the moist forest which is mostly secondary) of Tayrona Natural National Park (Rangel-Ch. and Lowy-C. 1995) on the north flank of the Sierra Nevada de Santa Marta (CPD Site SA25); this is one of the best preserved dry forests in the neotropics and deserves more international conservation attention. (In contrast, the nearby Salamanca NNP protects mostly dead mangroves, killed as a result of construction of the coastal highway.)
In Venezuela six National Parks encompassing almost 5000 km² protect coastal and insular ecosystems along the Coastal Cordillera, and eight National Parks encompassing some 5130 km² protect more mountainous parts of the entire Coastal Cordillera between Paria and San Luis, although some of them have largely second-growth vegetation. Especially significant is Henri Pittier NP (established 1937 - one of the early National Parks in Latin America), which includes not only an area of rich cloud forest but also a transect of Caribbeanslope dry forest.
Centres of Plant Diversity and Endemism
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