Location and General Description
The Sierra Nevada of Santa Marta montane forest ecoregion lies in northern Colombia between 10° 01’05’’ and 11° 20’11’’ north latitude and 72° 36’16’’ and 74° 12’49’’ east longitude, in the extreme northwest of South America. It is a mountain massif with a pyramid-shape and a surface area of 12,230 km2. On the shores of the Caribbean Sea these mountains rise to an altitude of 5775 m. This ecoregion forms a triangular shape. It’s northern edge runs just off the coast of the Caribbean Sea, while the western edge ends at the alluvial plane of the Magdalena River and Cienaga Grande, finally the Cesar and Ranchería River valleys form its southern border.
Its geology is complex with rock outcroppings of different types and ages including rocks of granitic, dioritic and quartz monzonitic batholiths that originated during the Mesozoic and Tertiary periods as volcanic rock and a varied sequence of sediments. The entire formation rose several kilometers between the Miocene and Upper Pleistocene (Bartels 1984). It is considered a bio-geographic island that is separate from the Andes Range. This mountain range lies along a north-northwest line and reaches heights that provide continuously snow-topped peaks. Above 3000 meters, glacially formed lakes are the source of the largest rivers that descend its slopes running trough this ecoregion to eventually irrigate the dry and warm plains that surround its lowlands.
Climate is determined by the latitudinal position of the mountain range as well as altitudinal variation and fluxuations of the northeast trade winds, against which it rises like an obstacle along the coastal plane of the Caribbean Sea. Air temperatures range from averages of 27° C at sea level to 6° C or less in the highest areas. The distribution of rain follows a bimodal pattern, with rainfall peaks between September and December and between May and July. There are also two dry periods between January and April and July and August. Average rainfall is higher on the north slope, where it can reach 3000 mm per year at altitudes between 1000 and 1500 m, then decreasing at higher altitudes.
In the central strip of the northern coast area, mountain rains determine the presence of forest cover, with trees up to 35 m high. Palms, arborescent ferns and large-leaved grasses form the forest’s understory. These forests of the northern section are found at altitudes of up to 900 meters and may correspond to the tropical rain forest, neotropical forest (Cuartrecasas 1958) or equatorial forest (Cleef et al. 1984). On the less moist western side, there is forest between 800 [and] 1000 m. ASL. (Carbonó & Lozano 1997). The most characteristic species are large trees such as Poulsenia armata, Virola sebifera, Pterygota colombiana, Guarea guidonia, Castilla elastica, Ficus macrosyce, Persea americana and the palm (Dictyocarium lamarckianum).
Above 900 m. in altitude, there are smaller trees and palms such as Pithecellobium longifolium, Euterpe precatoria, Geomoma oxicarpa and the arborescent fern Trichipteris procera; many vascular epiphytes, Vriesia elata, Guzmania lingulata, large-leaved understory plants Calathea insignis, Diffenbachia longisphata; mosses and hepatics, Octoblepharum albidum, Leucomium compressum.
Above 1000 m there are cloud forests. Between 1150 and 2500, the trees are leafy with a canopy between 25 and 35 m tall and the undergrowth has arborescent ferns and palms, many plants with prop roots and abundant vascular epiphytes and woody lianas. With its high moisture and frequent fogs, it has been characterized as sub-Andean forest (Cuatrecasas, 1958; Hernandez-C. & Sanchez, 1992). Characteristic species are Dictyocarium lamarckianum, emerging from the canopy and dominant in wet areas and slopes, Calatola costaricensis, Gustavia speciosa, Tovomita weddeliana, Cavendishia callista, Granfferieda santamartensis. Bryophytes are abundant and include Dumortiera hirsuta and Phyllogonium fulgens.
Between 2500 and 3300 m we have the cloud forest where fog is high and mists frequent, although precipitation may be less than in the previous area. There are formations with arboreal and arborescent elements between 15 and 20 m high. Characteristic species include Myrcianthes ternifolia, Chaetolepis santamartensis, Hesperomeles lanuginosa, Paragynoxys undatifolia, Weinmannia pinnata, Myrsine ferruginea, Podocarpus oleifolius, Ceroxylon ceriferum, Monochaetum uberrimum, Chusquea tuberculosa. Bryophytes and lichens including Anastrophyllum auritum, Campylopus benedictii, Funaria hygrometrica, Romalia dictyota, Hypotrachyna gigas also grow at this altitude. This strip is characterized as Andean forest (Hernandez-C. & Sanchez 1992; Cleef et al. 1984).
The Sierra Nevada de Santa Marta has warm wet forests on its northern flank and part of the western flank that are now isolated from other warm and wet forests. The specific plant diversity of these forests is considered relatively low (Prance 1982) although there are some endemic species. Thus it is considered important as a Pleistocene refuge, although diversity is limited in comparison with other ecoregions in the Neotropics.
The flora of the wet lowland forests is different from that in the cloud forests of the middle and high mountain areas and they have little in common. There are few vascular species with range from sea level to the high mountain forests. Cleef et al. (1984) found similarities, in terms of genera and species, between the wet forests of this Sierra ecoregion and forests in Panama, the Serranía de San Luis on the Venezuelan coast and the Serranía de Macuira in Colombia. They also found similarities in terms of physiognomy and flora with mountain forests in Costa Rica and Chocó ecosystems, in Colombia. At the level of family there are references to similarities with species of the Amazon, especially in the equatorial and sub-Andean forests. The high cloud forests have elements common to the tropical Andean and the high forests of the Caribbean. Also to be noted is the observation of an altitudinal depression with biotic zones and temperate level elements that can descend to lower altitude zones (Hernandez et al, 1992 a ; Lozano, 1984).
The greatest plant diversity in the Sierra is found between 1000 and 2500 m (Rangel & Garzon 1995). In this strip the angiosperm families with the most genera are Asteraceae (35), Orchidaceae (20), Leguminosae (20), Rubiaceae (20). These mountain forests have many endemic species of plants and animals. Among the vascular flora, families of particular interest are Melastomataceae, Bromeliaceae, Asteraceae and Lamiaceae and, among them, the genus Monochaetum (Melastomataceae) has five endemic species, as does Tillandsia (Bromeliaceae). Two endemic genera of the mountain forests of this ecoregion are reported as Kirkbridea (Melastomataceae) (Wurdack 1976) and Castenedia (Asteraceae) (King & Robinson 1978).
The family Melastomataceae represents the group with the largest number of endemic species (13) (Carbonó & Lozano 1997). Granfferieda santamartensis, Huliaea kirkbridei and Monochaetum magdalenense stand out for their abundance in some areas. Abundant populations of palms are common in the middle mountain ranges: "tagua" or ivory palm (Dictyocarium lamarckianum) between 900 and 1600 m and "palma de cera" or wax palm (Ceroxylon ceriferum) between 1800 and 2500 m.
Animal species and subspecies with restricted ranges are known to occur in this and surrounding ecoregions. Birds include Xiphocolaptes promeropirhyncus sanctamartae and the "trepatroncos" Lepidocolptes lacrymiger sanctamartae, Myoborus flavivertex, Pyrrhura viridicata, Ramphomicron dorsale, Oxypogon guerinii cyanolaemus, Lafresnaya lafresnayi liriope, and the Pharomachrus fulgidus festatus. Endemic birds listed by Stattersfield (1998) include the Santa Marta parakeet (Pyrrhura viridicata) and the white-tailed starfrontlet (Coeligena phalerata). Endemic saurians include Pseudogonatodes furvus, Anolis sanctamartae, Ptychoglossus ronalus and Proctoporus specularis. Amphibians include various species of Eleutherodactylus, especially in higher elevation zones, E. ruthveni, E. tayrona, E. cristinae, E. sanctamartae and a species of the only endemic genus of the Sierra Nevada, Geobatrachus walkeri (Hernandez et al. 1992b). Endemic mammals include the squirrel Sciurus granatensis saltuensis, Oryzomys villosus, Thomasomys monochromus and the otter Lutra longicaudis annectens.
The associated fauna is diversified. Mammals include Colombian tapir (Tapirus terrestris colombianus), ocelot (Leopardus pardalis), jaguar (Panthera onca centralis), white-lipped peccary (Tayassu pecari), agouti or "ñeque" (Dasyprocta punctata), paca (Agouti paca), red howler monkey (Alouatta seniculus). There are various bird species such as the keel-billed toucan (Ramphastus sulfuratus), black-chested jay or "chau-chau" (Cyanocorax affinis), Tangara gyrola, Arantinga wagleri, Pharomacrus fulgidus festatus, blue-knobbed curassow or "paujil" (Crax alberti), crested guan or "pava" (Penelope purpurascens brunnescens), Chlorostilbon russatus and Anthocephala floriceps floriceps (UAESPNN, 1998). There are also a large variety of reptiles, amphibians and insects.
According to Stattersfield (1998) much of this ecoregion has been destroyed leaving about 15% of the original vegetation intact, mainly on the north-facing slopes. Although not much help to this ecoregion it is found within the limits of the Sierra Nevada de Santa Marta National Park and in 1980 the Cogui–Arsario Arhuaco indigenous reserve was created as a strategy for conserving the ecosystems and aboriginal cultures in this territory further. The Sierra Nevada de Santa Marta Biosphere Reserve and Tayrona National Park also hold parts of this ecoregion but offer it little formal protection as areas are continuing to be cleared (Stattersfield 1998). The jurisdiction of the indigenous reserve was subsequently expanded so that it now overlays and exceeds the area covered by the National Park.
The mountains of this Sierra ecoregion previously held a settlement of pre-Columbian aboriginal communities that left signs of their presence in various areas (Herrera de Turbay 1984). In addition, they have been settled at different times since the late nineteenth century. All of this led to a process that modifies the natural environment. The area covered by mountain forests has declined drastically during the last 50 years. In some cases, it is estimated that the reduction in the original forest is between 70% and 80% (Fundación ProSierra 1991).
Types and Severity of Threats
The low-lying wet forest has been highly affected by the opening of areas for settlements and the growing of marijuana (Cannabis sativa) and coca (Erythroxylon sp.), leaving only a few thinned-out and fragmented original stronghold forests. The landscape has also been changed by the creation of extensive pastures, the removal of firewood and timber presenting problems associated with deforestation such as lack of soil protection resulting in erosion, silting of rivers, declining flows and avalanches or mud slides during the rainy seasons.
The mid-mountain strip is to a great extent a belt of coffee crops dating from the late nineteenth century. In addition, the increase of cattle ranching and the removal of wood has created extensive areas of pasture that are maintained by annual burns. The cloud forests of the high mountains appear changed and simplified in the altitudinal limit with the high plateau where sheep and cattle are raised, potato and fruits are grown and useful woods are extracted. Some basins that have been inhabited for many years leaving corridors of pasture and secondary vegetation extending from the lowlands to the high plateau. These include the basins of the Ancho and Frío rivers. Hunting has reduced the populations of large animals. The tapir (Tapirus terrestris), deer (Mazama americana) and carnivores like the jaguar (Panthera onca centralis), puma (Puma concolor) and ocelot (Leopardus pardalis) are under threat of extinction due to the reduction of forested areas. Other species such as the white-lipped peccary or "zaíno" (Tayassu pecari), the paca or "quartinaja" (Agouti paca), the agouti or "ñeque" (Dasyprocta punctata), the red howler monkey (Alouatta seniculus), birds like the crested guan or "pava" (Penelope purpurascens) are hunted by settlers and indigenous inhabitants. Jaguars and pumas are hunted as the enemies of cattle ranchers and ocelots are hunted as predators of poultry and to sell their skins.
Grave looting is another source of deterioration caused by the opening of high forest areas where pre-Columbian archeological remains are found creating roads, increasing hunting and extraction of firewood due to new accessibility. Despite the conservation policies included in national and international conventions and agreements, there is no focus on the balanced use of resources nor are there any effective preservation and management measures adequate to preserve the biological importance of the area.
Justification of Ecoregion Delineation
This isolated mountain range is separated from the Cordillera Oriental of the northern Andean chain by a swath of xeric habitat, and its species assemblages and characteristics reflect this isolation with many endemic species. Delineation for this ecoregion are to include the moist forests from the lowland dry-xeric transition (500m) up to the páramos vegetation transition (3000m) which characterizes the tops of these mountains. Linework was drawn initially to follow the Suarez-Navarro et al. (1984) vegetation classifications of "heterogenous species forest on hills with abrupt relief", "heterogenous species forest on hills of moderate relief", and "montane forests of the escarpment zone". Linework was later reviewed and modified during a workshop on Northern Andean ecoregions (Bogota, Colombia, 24-26, July, 2000), to better represent historic coverage.
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Prepared by: Eduino Carbono, Herbario Universidad del Magdalena. Santa Marta. Colombia.
Reviewed by: Emilio Constantino