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CENTRES OF PLANT DIVERSITY AND ENDEMISM.
II. Guayana Highlands
The Guayana Highlands are defined here as a distinct floristic entity extending between (1300-) 1500-3000 m, comprising all upper table mountains ("tepuis") located within the area of the ancient Guayana Shield. There are approximately 50 different tepui summits ranging in elevation between 1800-2500 m, which are concentrated mostly in southern Venezuela, with a few outliers in Brazil (Pico da Neblina) and Guyana (Mounts Ayanganna and Wokumung). The Guayana Highlands thus occupy a fragmented area of approximately 20,000 km≤, which is embedded in the northern border region of Amazonia and is limited farther to the north by the Caribbean region. Others (e.g. Huber 1987, 1994) consider the Guayana Highlands instead as a province of a phytogeographically separate region, the Guayana region, calling this distinctive high-mountain area Pantepui.
Although the Guayana Highlands flora is not exceedingly rich (approximately 2300 species - Berry, Huber and Holst 1995), its level of endemism is high (c. 65%) and mainly restricted to the tepui summit vegetation. The mountain systems of Neblina, ChimantŠ, Duida-Marahuaca and AuyŠn-tepui have the highest endemism. Endemism is particularly concentrated in the families Theaceae, Rapateaceae, Ochnaceae, Compositae (tribe Mutisieae), Bromeliaceae, Xyridaceae and Eriocaulaceae; in addition there are one to three endemic families - the fern family Hymenophyllopsidaceae and the perhaps good families - Tepuianthaceae and Saccifoliaceae. The high-tepui flora also contains a number of Andean taxa, especially amongst Ericaceae, Winteraceae and Podocarpaceae, with several locally endemic genera and species.
Another outstanding feature of the Guayana Highlands is its remarkable ecological diversity, which is most pronounced in the herbaceous and scrub formations. Many peculiar life forms are found in these ecosystems, such as the tubular herbs of Brocchinia (Bromeliaceae) and Heliamphora (Sarraceniaceae), the two-ranked (distichous) broadleaved herbs of Stegolepis, Marahuacaea and Phelpsiella (all Rapateaceae) and the strange stalked-rosette shrubs of Bonnetia (Theaceae) and Chimantaea (Compositae).
Many indigenous tribes of the surrounding lowlands consider the tepuis as mythical or sacred mountains with inaccessible or forbidden summits; therefore the plants of this region are unknown to the Amerindians rather than being used. The present economic importance of the tepui flora lies mainly in its genetic potential. Some species are beginning to be sought after by plant hunters for horticultural purposes, such as the species of Heliamphora and some particularly attractive orchids and bromeliads.
The main threat to the tepui flora and vegetation is increasing mass tourism. Many species are very fragile or brittle and do not withstand major physical impact (e.g. trampling or other mechanical damage). Furthermore, due to their low fire resistance, escaped or intentional fires originating from tourist camps represent one of the main threats to these unique vegetation types.
At present all tepui summits of the Venezuelan Guayana Highlands are protected in six National Parks, 28 Natural Monuments and one Biosphere Reserve, which were declared during recent years. However, only two National Parks (Canaima and Duida-Marahuaca) have their management plans legally approved, and their implementation is limited by severe understaffing.
Centres of Plant Diversity and Endemism
Venezuela, Brazil, Guyana
SA2. Pantepui region of Venezuela
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