Location and General Description
These dramatic features in the landscape perforate an extensive matrix of highland savannas and rain forests across southern Venezuela mostly, with a few outliers in western Guayana, Surinam, and northern most Brazil. Hundreds of smaller sandstone mountains exist in the ecoregion as well. The Tepuis are characteristically flat-topped steep, nearly vertical escarpments interrupted by terraced talus slopes. Some mountains present more undulating irregular summit contours. Each mountain displays its own spectacular characteristics of shape, biodiversity or elevation. The highest peaks are Pico da Neblina in Brazil at 3,014 m, the adjacent Pico Phelps (2,992 m) in Venezuela, followed by Roraima-tepui (2,810 m) and Cerro Marahuaka (2,800 m), both in Venezuela. Cerro Ichún, close to the Brazil-Venezuela border, has the largest surface area of all the sandstone tabletop mountains with a total area of 3,260 km2 at an elevation of 1,400 m. On the highest summits, the temperature can drop to an extreme of 0° C, but generally the temperatures on the summits range from 8° to 20° C on average over the year, depending on elevation. The Tepuis are constantly humid and receive from 2,000 to 4,000 mm of rain per year with a subtle dry season. Soils are generally oligotrophic (low nutrient).
The Guayana Shield, on which the Tepuis rest, consists of a rock basement with a variety of igneous and metamorphic rock types formed during different geological periods beginning 1.8 billion years ago. Most of this granitic basement was overlain with many layers of sand that were subsequently compressed and cemented together to a thickness of several thousand meters to form quartzitic and sandstone rocks. Following the uplifting of this once-continuous layer, subsequent erosion resulted in the separation and isolation of the Tepui Mountains, approximately 180 million years ago. These remnants of highly weathered and ancient parent rock are some of the oldest geological formations in all of South America.
The vegetation on the Tepui Mountains is distinct from the surrounding Amazonian humid forest vegetation and forms a biogeographic complex. It is called the Pantepui floristic province , although is has a discontinuous distribution as it only encompasses the ecosystems above 1,500 m. Floristic associations vary from mountain to mountain. The ecoregion is characterized mostly by a diversity of montane shrublands, meadows, open rock communities, and forests. There is an extraordinary degree of species richness on these isolated mountaintops, and they host some of the highest plant endemism in northern South America. Of the 2,322 species of vascular plants in 630 genera in the floristic province, 766 (33) are endemic to the province, and 65 are restricted to the Guayana Shield .
A representative tepui hosts four distinct vegetation zones starting at the base, proceeding to the talus slope, on to the base of the escarpment (cliff), and finally the mountain summit . The base of the mountain arises out of either highland savanna or evergreen rainforest at elevations below 500 m elevation. The uninterrupted mat of rainforest between mountains, with a canopy between 25 and 45 m tall, is dominated either by lowland Amazonian or Guayana elements (these ecoregions also have distinct floras). The Amazonian families included are Lauraceae, Magnoliaceae, Elaeocarpaceae, Rubiaceae, and Myrtaceae . Humid montane forests sit on the talus slopes above 500 m elevation with trees of a tall stature (to 60 m). Eventually, lowland genera drop out from the upper slopes giving way to members of the montane genera Clusia, Monorobea, Miconia, Graffenrieda, Magnolia, Myrcia, Drimys, and Viburnam. Species of the typically tropical highland or temperate Ericaceae become common in these cloud forests along with ferns. On these cooler, humid forests of the upper talus slopes, species of Andean ancestry have evolved. Moving up to the base of the escarpments, most plants are hardy individuals jammed in the crevices or eking out an existence on the bare sandstone strata. These plants belong to species that have evolved in close association with this type of habitat. Members of the Bromeliaceae (pineapple family) are particularly successful here, especially in the genera Cottendorfia, Navia, and Brocchinia.
The summit vegetation is of particular interest, and it is here that the high endemism characteristic of the Tepui floristic province is found. Five vegetation types are found on the summits: 1. forests of tall or dwarfed trees, including riverine forests; 2. epiphytes in forest associations; 3. shaded crevices of rocks, bluffs and ledges; 4. wet or dry open savanna without rock outcrops; and 5. exposed rock outcrops, open sandy or rocky areas . Some summit endemics occur on most or all mountains, such as the insectivorous species Drosera roraimae and Urticularia humboldtii. Others are highly localized, occurring only on a single summit; 18 of these endemic taxa have been identified on the Tepuis. Forests on the summits, when present, are low (8-15 m), species-poor, and restricted to streamsides and large depressions. Some vegetation associations in these low forests are Bonnetia neblinae and Neotatea neblinae; Podocarpus roraimae, Schefflera umbellata, Daphnopsis steyermarkii, Psychotria jauaensis, Befaria sprucei, and Weinmannia velutina; and the endemic-dominated association on the Cerro Yapacana of Bonnetia tristyla, Tepuianthus yapacanensis, Symplocos yapacanensis, and Gongylolepis yapacana.
The Tepui ecoregion as a whole comprises four phytogeographic districts based on floristic and geographical criteria, each grouped into mountain blocks, and each containing its own set of characteristic and endemic taxa . The Eastern District is delimited by the distribution of the endemic treelet Bonnetia roraimae. Some genera endemic to this district include Quelchia, a shrubby genus of the sunflower family; Connellia, in the Bromeliaceae; and Tepuia, in the Ericaceae (blueberry family). The Southern District, along the eastern Venezuela-Brazil border, host extensive shrublands, meadows, and frequent low forests. This region has the highest number of endemic flowering plant taxa with one endemic family (Saccifoliaceae) and twelve endemic genera. The Western District is the most extensive of sandstone and granitic mountains hosting the characteristic red-flowered Kunhardtia rhodantha, shrubby melastomes Graffenrieda and Meriania, and a number of endemic Phyllanthus species. The final phytogeographic district, the Jaua-Duida District comprises widespread summits sharing genera such as Tyleria, Neotatea and Tepuianthus, as well as the dominant meadow species Stegolepis grandis.
The vegetation on the Tepuis shows very high endemism (33%). A total of 20 species of the bamboo genus Myriocladus are endemic to the Tepuis. Plant genera endemic to the Tepuis ecoregion include Brewcaria, Tepuia, Celiantha, Neblinantha, Pyrrorhiza, Comoliopsis, Mallophyton, Adenanthe, Aracamunia, Marahuacaea, Coccochondra, Rutaneblina, Saccifolium, Achlyphila, and many others . Many orchids and insectivorous plants are also present.
The Tepuis ecoregion hosts 186 mammal species, mostly located on the lower slopes of the mountains. This number includes 9 primates that live here including howler monkeys(Alouatta seniculus), night monkeys (Aotus trivirgatus), titi monkeys (Callicebus torquatus), black uakari (Cacajao melanocephalus), weeper capuchins (Cebus olivaceus), and white-faced sakis (Pithecia pithecia). Five cats live here, including jaguars (Panthera onca) and pumas (Puma concolor). Some mammals are restricted to this region of Amazonia; these include an endemic opossum (Marmosa tyleriana) and white-eared opossum (Didelphis albiventris), long-tailed weasels, pale-throated sloths and a great variety of bats (Diclidurus isabellus, Pteronotus personatus, Phyllostomus latifolius, Anoura geoffroyi, Glossophaga longirostris), an endemic rodent (Podoxymys roraimae), three climbing rats in the genus Rhipidomys, and two guinea pigs (Cavia).
A large number of birds are found in the Tepuis ecoregion (628 species) with 41 endemics including tepui tinamous (Crypturellus ptaritepui), fiery-shouldered parakeet (Pyrrhura egregia), tepui parrotlets (Nannopsittaca panychlora), roraiman nightjars (Caprimulgus whitelyi), tepui swifts (Cypseloides phelpsi), rufous-breasted sabrewings (Campylopterus hyperythrus), buff-breasted sabrewings (C. duidae), peacock coquettes (Lophornis pavoninus), tepui goldenthroats (Polytmus milleri), velvet-browed brilliants (Heliodoxa xanthogonys), white-throated foliage-gleaners (Automolus roraimae), tepui antpittas (Myrmothera simplex), red-banded fruiteaters (Pipreola whitelyi), three manakins (Pipra cornutai, P. pipra, and Chloropipo uniformis), among many others.
Reptiles and amphibians are abundant on the summits and slopes of the Tepuis. The more ferocious snakes that occur here include fer-de-lance (Bothrops asper), coral snakes (Micrurus spp.), boa constrictors (Boa constrictor), and bushmasters (Lachesis muta). Iguanas (Iguana iguana) are ubiquitous and tegus lizards (Tupinambis spp.) common.
Due to the inaccessibility of both the steep slopes and high summits of the Tepui Mountains, much of the natural habitat is intact. However, there have been many anthropogenic changes. Human-induced fires at the base of the mountains have destroyed vegetation in extensive areas. The mountains above 800 m are designated protected conservation areas as natural monuments, national parks, or biosphere reserves. However, because of the remoteness of the mountains, enforcement of conservation regulations by reserve staff is difficult; illegal activities such as gold mining and burning proceed unchecked. The vegetation on the summits of some tepuis accessible by foot, in particular Roraima-tepui and Auyán-tepui, have suffered environmental contamination and damage at the hands (and feet) of visiting hikers .
Types and Severity of Threats
Visits to the Tepui summits by hikers and campers result in trampled vegetation, stripping of woody species for firewood, escaped fires, and littering; all of which threaten species and habitat . Illegal gold and diamond mining operations on the lower slopes of the Tepuis destroy not only vegetation, but also the very structure of the mountain. Human-induced fires on open savanna at the base of the Tepuis can reach the forests and rock outcrops on the slopes or even the summit. Huber has detected fire evidence on 10 summits. Recovery of the Tepuis’ vegetation is very slow probably because of the poor soils . Overhunting poses a threat to some mammals and birds. Global warming could have dramatic impact on the biodiversity of these mountains.
Justification of Ecoregion Delineation
Tepuis are internationally recognized as unique sandstone "inselberg" formations, emerging from the ancient Guayanan Shield, and who prolonged isolation and abrupt topography (among other things) have lead to a great many endemic species. In mapping these unique habitats we relied on a number of national vegetation coverage maps. Because this ecoregion characterizes the tops of these formations, it occurs as an archipelago formation from Brazil, across Venezuela, through Guyana, with the easternmost outlier in Suriname. In Venezuela we followed the Huber and Alarcon (1988) classification of "shrub-herbaceous high Tepui vegetation". In Brazil, IBGE (1993) does not distinguish this small portion from the "dense ombrophilous montane forest" – so we matched topographic lines across the border to encompass this Tepui called Pico da Neblina. In Guyana we followed the Huber et al. (1995) classification of low, evergreen high-Tepui forests and high-Tepui scrub. Finally, in Suriname we followed OAS (1988) to encompass the Tafelberg Tepui and vicinity.
Berry, P. E., O. Huber, and B. K. Holst. 1995. Floristic analysis and phytogeography. Pages 161-191 in P. E. Berry, B. K. Holst, and K. Yatskievych, editors, Flora of the Venezuelan Guayana. St. Louis, Missouri Botanical Garden and Timber Press.
Daly, D. C., and J. D. Mitchell. 2000. Lowland vegetation of tropical South America. Pages 391-453 in D. L. Lentz, editor, Imperfect Balance: Landscape transformations in the Precolumbian Americas. New York: Columbia University Press.
Fundação Instituto Brasilero de Geografia Estatástica-IBGE. 1993. Mapa de vegetação do Brasil. Map 1:5,000,000. Rio de Janeiro, Brazil
Huber, O., G. Gharbarran, and V. Funk. 1995. Vegetation map of Guyana (preliminary version). 1:1,000,000. Centre for the Study of Biological Diversity, University of Guyana, Georgetown, Guyana.
Huber, O., and C. Alarcon. 1988. Mapa de vegetación de Venezuela. 1:2,000,000. Ministerio del Ambiente y de los Recursos Naturales Renovables, Caracas, Venezuela.
Huber, O. 1995a. Conservation of the Venezuelan Guayana. Pages 193-218 in P. E. Berry, B. K. Holst, and K. Yatskievych (editors), Flora of the Venezuelan Guayana. St. Louis: Missouri Botanical Garden and Timber Press
Huber, O. 1995b. Geographical and physical features. Pages 1-61 in P. E. Berry, B. K. Holst, and K. Yatskievych, editors, Flora of the Venezuelan Guayana. St. Louis, Missouri Botanical Garden and Timber Press.
Huber, O. 1995c. Vegetation. Pages 97-160 in P. E. Berry, B. K. Holst, and K. Yatskievych, editors, Flora of the Venezuelan Guayana. St. Louis: Missouri Botanical Garden and Timber Press.
OAS & National Planning Office of Suriname. 1988. Suriname Planatlas. Organization of American States, Executive Secretariat for Economic and Social Affairs Department of Regional Development. Washington, D.C., USA.
Steyermark, J. A. 1986. Speciation and endemism in the flora of the Venezuelan Tepuis. Pages 317-373 in F. Vuilleumier and M. Monasterio, editors, High Altitude Tropical Biogeography. New York: Oxford University Press.
Prepared by: Robin Sears
Reviewed by: In process