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Guayana Highlands: CPD Site SA2

PANTEPUI REGION
of Venezuela

Location:  Phytogeographic province of Guayana Highlands, mainly in southern Venezuela, and as well in north-western Guyana and northernmost Brazil, between latitudes 0°-7°N and longitudes 60°-67°W.
Area: 
Province covers 6000-7000 km².
Altitude: 
.
1300-3015 m.
Vegetation: 
Upper montane evergreen tall forest, upper montane evergreen low forest ("tepui" forest), evergreen tepui scrub, tepui fields, open-rock pioneer vegetation.
Flora: 
Very high diversity (probably c. 3000 spp.), very high endemism of genera and species, with large number of disjunct taxa of tropical montane and extra-tropical floras.
Useful plants: 
Plant resources other than ornamentals yet to be utilized, but undoubtedly potentially rich in genetic resources.
Other values: 
Fauna refuge, endemic animals; watershed protection for drinking water and hydroelectric energy; tourist attraction.
Threats: 
Increasing tourist pressure, roads, airstrips; over-collecting; mining; fire.
Conservation: 
6 National Parks, 28 Natural Monuments and 1 Biosphere Reserve cover this province in Venezuela.

Map 38: CPD Site SA2
References

Geography

The phytogeographic province of Pantepui forms part of the floristic region of Guayana (Huber 1994) and includes all upper slopes and summits of the characteristically flat-topped table mountains ("tepuis") (picture) of the Guayana Highlands. Pantepui, a term established by Mayr and Phelps (1967) and subsequently used with different meanings (Huber 1987), is mainly located in southern Venezuela, where there are more than 90% of the mountains of this type (Map 38), with some lower outliers in north-western Guyana and northernmost Brazil.

The Guayana Highlands are drained principally by the Orinoco River with its southern and eastern affluents, and to a minor extent by the Cuyuni and Mazaruni rivers in Guyana and the Branco and Negro rivers in northern Brazil. The regional geology consists of an igneous (mainly granitic) Precambrian base (the Guayana Shield), overlain by younger Precambrian meta-sedimentary sandstones and quartzites of variable thickness - 100 m to more than 3000 m. These predominantly horizontally bedded sandstone layers, belonging to the Roraima Formation, have been intruded repeatedly and in many places by more recent igneous and volcanic materials, resulting in a variety of mainly diabasic sills and dykes at intermediate and upper elevations (Schubert and Huber 1990).

The physiography of Pantepui typically shows an altitudinal sequence of more or less inclined piedmont slopes followed by vertical sandstone walls up to 1000 m high, surmounted by generally flat but broken summit plains, which in some places alternate with rounded hill-and-summit topography typical of diabasic intrusive areas. The mountains vary greatly in size and form, ranging from tower-like, needle-pointed isolated peaks (e.g. Cerro Autana, Wadakapiapue-tepui, Cerro Aratitiyope) with less than a hectare of summit surface, to huge mountain systems of up to 600 km² or more like those of Auyán-tepui, Chimantá massif, Jáua, Duida and Neblina. Extensive peats have developed on many summit areas. All the soils are highly acidic and extremely nutrient poor.

The climate reflects the equatorial position of Pantepui: a rather equilibrated annual thermic regime (with mean annual temperatures ranging between 20°-8°C according to altitude) contrasts with extremely pronounced variations in the daily regime (with variations of up to 20°C). The lowest recorded air temperatures are around 1°-2°C (on the summit of Mt Roraima, at 2740 m); frost has never been convincingly measured, though it may well occur occasionally on the highest peaks, above 2800 m. Annual rainfall varies between 2000 and 4000 mm, with a slight decrease during January to March, but no true dry season has been observed on any tepui summit. Strong winds (mainly north-east trade winds) during a greater part of the year, coupled with high irradiance, certainly cause high evapotranspiration, but probably compensated by permanently high humidity.

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Vegetation

The vegetation of this extensive area varies greatly according to altitude and the fragmented nature of this discontinuous mountain region. On a recent vegetation map of Venezuela (Huber and Alarcón 1988), no fewer than 14 different vegetation types are shown (based on physiognomic, ecological and floristic criteria). Broadly, there are four main vegetation formations: arboreal (forests), shrub (scrub), herbaceous (meadows and savanna-like "campos") and pioneer (on rock outcrops and walls).

1. The forest formation includes a series of montane forest types, covering not only the upper slopes of the base of the tepuis, but also some portions of the summits, especially on diabasic hills, or along creeks or in depressions. Whereas the slope forests are amongst the tallest (up to 60 m) and densest reported for Venezuela (J.J. Wurdack, pers. comm.), the summit forests ("tepui" forests) are dense but seldom higher than 812 m and relatively simple in their structure and floristic composition. Typical and dominant trees of the summit forests belong to such genera as Bonnetia, Schefflera and Stenopadus, whereas in slope forests Lauraceae, Magnoliaceae, Elaeocarpaceae, Rubiaceae and Myrtaceae are among the most frequent families.

2. The scrub formation has the highest diversity, with a variety of both physiognomically and floristically distinct communities. Almost all the larger tepui summits have their own types of scrub, ranging from low (less than 2 m) and open, to tall (3-5 m) and very dense communities, with high floristic diversity. Especially remarkable are páramo-like scrub types on Chimantá formed by dense colonies of stem-rosette Compositae, and extremely scleromorphic and thick-stemmed Bonnetia populations on Neblina, Duida and Chimantá.

3. The herbaceous formation is also floristically and morphologically diverse. The dominance of various members of Rapateaceae (e.g. Stegolepis, Kunhardtia) in these high mountain fields, together with Xyridaceae, Cyperaceae and Eriocaulaceae, is one of the outstanding features in almost all summit landscapes; grasses are usually not dominant and belong mainly to the subfamily Bambusoideae. These "campos", attaining heights of 0.5-2 m, are generally quite dense and best developed on deep organic substrates.

4. The pioneer formation colonizing extensive open-rock areas on summits, and on walls of the flanks of the tepuis, exhibits remarkable ecological and floristic diversity. The dominant life forms are terrestrial rosettes of Bromeliaceae (e.g. Navia, Lindmania, Brocchinia). There are also many different lichens, hepatics and mosses, which as colonizers on organic and inorganic substrates, occupy main niches.

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Flora

A Flora of the entire region of Guayana in Venezuela is in an advanced stage of preparation; of the more than 9000 species, probably 3000 are found in Pantepui. According to Steyermark (1986), some 460 genera in 97 families are known to occur on the tepui summits (picture) and slopes. Numerically, the most important families are Orchidaceae, Bromeliaceae, Melastomataceae, Rubiaceae, Eriocaulaceae, Xyridaceae, Ericaceae and Compositae.

Apart from the species richness, the phytogeographic province also shows very pronounced floristic autochthony, resulting in a high degree of endemism and ecologically restricted populations of widely disjunct taxa. The Pantepui Province is probably one of the main centres of endemism of the neotropics; compared to its small overall surface, it probably contains the highest number of endemic taxa per unit area. Known endemics thus far include one fern family (Hymenophyllopsidaceae), one flowering plant family (Saccifoliaceae) and 39 summit genera, of which the most important are found in Theaceae, Rapateaceae, Ericaceae, Compositae, Bromeliaceae, Rubiaceae and Melastomataceae (Steyermark 1986).

Some parts of the Pantepui Province have a greater concentration of endemic taxa than others: Cerro de la Neblina in the extreme south is likely to hold the most endemic genera, followed by the Chimantá massif and Duida-Marahuaca. At least five well-defined centres of endemism can be distinguished in Pantepui (Map 38), ranging from the eastern tepui chain (Roraima-Ilú), to the central massifs of Jáua-Sarisariñama, passing through the north-western group of Yaví-Sipapo and ending in the southern Neblina-Aracamuni massif (Huber 1987).

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Useful plants

Since no people lived in the upper regions of the Guayana Highlands, their plant resources have not been utilized. However, the many endemic taxa undoubtedly represent a considerable genetic resource, which might reveal interesting biochemical properties when thorough analyses are realized. Furthermore, these complex high-mountain ecosystems contain an impressive number of plants with specialized adaptations to various environmental factors. As such, they represent important subjects for study of still unknown ecological and functional structures and processes.

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Social and environmental values

The Pantepui vegetation is an important rainfall interceptor in the uppermost portions of the different river basins, which are increasingly utilized to generate hydroelectric power. It is necessary to maintain the hydrological equilibrium in the upper basins in order to assure a regular supply of water for power and drinking (e.g. Galán 1984).

The beautiful and impressive table mountains (tepuis) of the Guayana Highlands are a most attractive South American mountain landscape. Indeed, tourist interest in this region increases from year to year, due to easier access and wider publicity, both nationally and internationally.

The Pantepui region (Endemic Bird Area B02) is home to 36 bird species totally restricted to the vicinity of the tepui mountains. They are primarily montane species occurring in the humid forest on the piedmont slopes above c. 600m; the swift Cypseloides phelpsi is confined to the vertical cliffs, and Emberizoides duidae is confined to the herbaceous vegetation of the summits (Cerro Duida). Most of the endemics are to be found on the Gran Sabana, although a number of species are confined to lone, isolated tepuis. Due to the limited habitat disturbance in this region, none of the endemics is considered threatened currently.

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Threats

There are no serious threats as yet to the existence of the Pantepui flora and vegetation. However, mass tourism is just beginning, and already some mountains (such as Roraima and Auyán-tepui) show the impacts of uncontrolled visitation (e.g. accumulation of litter, destruction of vegetation for campsites, exploitation of crystals for souvenirs). Canaima, the largest National Park in Venezuela (30,000 km²), is affected by rapidly growing mass tourism, which is favoured by road construction, illegal airstrips and helicopter flights into previously inaccessible areas. There is a great danger of fire accidentally spreading from campsites, which could lead to the destruction of large sections of summit vegetation. Such vegetation seems to need extremely long periods for recuperation.

One south-western tepui, Cerro Yapacana, although of lower altitude and not actually within the Pantepui Province, is suffering heavily from uncontrolled mining activities at its base and on the slopes. Since 1978, when Yapacana National Park was declared, the gold mining has taken place illegally.

There is a risk of scientific over-collection in certain Pantepui ecosystems: some summits are only covered by a very sparse vegetation in which many species are extremely rare. Hobbyists and commercial collectors pose a threat to some of the more ornamental plants, such as orchids, bromeliads and various carnivorous plants (which remarkably include a few bromeliads).

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Conservation

For 10-25 years, important parts (30-40%) of the Pantepui Province in Venezuela were included in five National Parks (Canaima, Jáua-Sarisariñama, Yapacana, Duida-Marahuaca, Neblina) totalling 52,200 km² and in one natural monument (Cerro Autana). From January 1991, the entire province was brought into such protection, and a Biosphere Reserve has been declared. However, more effective controls and enforcement of the regulations are needed, and biologists' evaluation of the impacts.

Regional development agencies sometimes act in an ambivalent manner, sponsoring tourism, mining, logging and other exploitive activities, but also strongly supporting river-basin protection for hydroelectric schemes. Fortunately in recent years national and international concern has grown vigorously for better and more thorough protection of this important region, leading to a powerful new legislative initiative to establish all tepuis over 800 m above sea-level as natural monuments. With their new status (6 NPs, 28 NMs, 1 BR) in Venezuela, the entire Pantepui Province may continue to exist as the outstanding and unique biological treasure of the Guayana region, and not become a "lost world", as it is often but quite inappropriately called.

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Map 38. Pantepui Region, Venezuela (CPD Site SA2), showing principal mountain systems ("Tepuis")

References

Galán, C. (ed.) (1984). La protección de la cuenca del Río Caroní. C.V.G. Electrificación del Caroní, C.A. 51 pp.

Huber, O. (1987). Consideraciones sobre el concepto de Pantepui. Pantepui 2: 2-10.

Huber, O. (1994). Recent advances in the phytogeography of the Guayana region, South America. Mém. Soc. Biogéogr. (3ème série) 4: 53-63.

Huber, O. and Alarcón, C. (1988). Mapa de vegetación de Venezuela. 1:2,000,000. Ministerio del Ambiente y de los Recursos Naturales Renovables and Fundación BIOMA, Caracas.

Mayr, E. and Phelps Jr., W.H. (1967). The origin of the bird fauna of the South Venezuelan Highlands. Bull. Amer. Mus. Nat. Hist. 136: 269-328.

Schubert, C. and Huber, O. (1990, English ed.; 1989, Spanish ed.). The Gran Sabana: panorama of a region. Lagoven, S.A., Caracas. 107 pp.

Steyermark, J.A. (1986). Speciation and endemism in the flora of Venezuelan tepuis. In Vuilleumier, F. and Monasterio, M. (eds), High altitude tropical biogeography. Oxford University Press, New York. Pp. 317-373.

Author

This Data Sheet was written by Dr Otto Huber (Research Associate, Apartado 80405, Caracas 1080-A, Venezuela).

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