Acta Botanica Venezuelica ISSN: 0084-5906 [email protected] Universidad Central de Venezuela Venezuela ARANGUREN B., Anairamiz; COSTA, Manuel; GUEVARA, José; CARRERO, Omar PHYTOBIOGEOGRAPHY OF THE SPECIES ASSOCIATED WITH DRY INTERMOUNTAIN VALLEYS IN THE CHAMA RIVER MIDDLE BASIN, MÉRIDA, VENEZUELA Acta Botanica Venezuelica, vol. 38, núm. 1, 2015, pp. 63-85 Universidad Central de Venezuela Caracas, Venezuela Available in: http://www.redalyc.org/articulo.oa?id=86245429004 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative ACTA BOT. VENEZ. 38 (1): 63-85. 2015 63 PHYTOBIOGEOGRAPHY OF THE SPECIES ASSOCIATED WITH DRY INTERMOUNTAIN VALLEYS IN THE CHAMA RIVER MIDDLE BASIN, MÉRIDA, VENEZUELA Fitobiogeografía de especies asociadas a un valle intermontano seco en la cuenca media del río Chama, Mérida, Venezuela Anairamiz ARANGUREN B.1, Manuel COSTA2, José GUEVARA3 y Omar CARRERO3 1Instituto de Ciencias Ambientales y Ecológicas. Universidad de Los Andes (ULA). Mérida. Venezuela [email protected] 2Institut Canavilles, Jardín Botánico de la Universitat de València, España 3Herbario MER. Facultad de Ciencias Forestales y Ambientales de la Universidad de Los Andes (ULA). Mérida. Venezuela ABSTRACT Dry intermountain valleys in the Andes constitute areas of ecological interest due to their unique climate, flora, and soils. In the state of Mérida (Venezuela), a xerophytic or semiarid enclave located in Ejido-Estanques in the middle basin of the Chama river was studied. The floristic inventory showed 28 families with 62 species (3 endemics) and seven new reports. The phytogeographic analysis indicates that all species belong to two floris- tic kingdoms, except for two cosmopolitan and cultivated species. Nine biogeographical regions and 37 provinces are represented, belonging to the Neotropical-Austroamerican kingdom, the Neotropical subkingdom. The most frequent are the Colombian Andean and Guajirean-Caribbean provinces, although other species have a Caribbean-Mesoamerican and Guayanan-Orinoquian origin. There are several natural ecosystems which suggest a drier climate in the past, with different floristic elements from those in adjacent more humid ecosystems. Key words: Chama river, dry intermountain valley, Mérida, phytobiogeography, Venezuela RESUMEN Los bolsones xerofíticos de los Andes de Mérida constituyen enclaves de interés eco- lógico dadas sus condiciones únicas climáticas, edáficas y florísticas. En el estado Mérida (Venezuela) se estudió el bolsón xerofítico o enclave semiárido en Ejido-Estanques, en el valle medio del río Chama. El inventario florístico revela 28 familias, 62 especies, de las cuales tres son endémicas y siete son nuevos registros para la zona. El análisis fitogeográfi- co muestra dos reinos aunque hay dos especies cosmopolitas y cultivadas. Nueve regiones biogeográficas y 37 provincias están representadas, pertenecienets al reino Neotropical- Austroamericano, subreino Neotropical. Resaltan como frecuentes la provincia Andina Co- lombiana y la Guajireña-Caribeña de la Neogranadina; también se encontraron plantas de origen Caribe-Mesoamericano y de la región Guayana-Orinoquense. Hay varios ecosiste- mas naturales que revelan un clima seco en el pasado y elementos florísticos muy disímiles de los ecosistemas aledaños. ISSN 0084-5906 Depósito Legal 196902DF68 Depósito Legal (Internet) ppi 201402DC4561 Recibido: 27/06/2014 Aceptado: 24/09/2015 64 Aranguren, Costa, Guevara y Carrero Palabras clave: Fitobiogeografía, Mérida, río Chama, valle intermontano seco, Venezuela INTRODUCTION Arid zones are common throughout the Andes, a consequence of low pre- cipitation, the causes of which are varied. Dry conditions are often the result of be- ing in a rain shadow, as is the case in Argentina (Sarmiento 1975), Ecuador (Emck et al. 2006), Chile (Di Castri & Hajek 1976), and Perú (López 2003). In other ar- eas, low rainfall is a result of cold ocean currents, as is the case in the American Pacific Desert of Perú and Chile (Weberbauer 1945, cited by Emck et al. 2006; Koepcke 1961, cited by Sarmiento 1975; Rundel et al. 1991; Galan de Mera et al. 2011). Lower precipitation levels may also result from being situated in an in- land valley, which prevents the entry of moisture-laden winds of oceanic origin. This is the case of the xerophytic or semiarid enclaves of the northern Andes, with examples in Colombia (Pamplonita, Chicamocha, and Magdalena) as well as in Venezuela (Cuatrecasas 1958; Sarmiento 1975; Rangel et al. 1997; Albesiano & Fernández-Alonso 2006; Visconti et al. 2013). The most impressive xerophytic enclaves in Venezuela are located in the states of Trujillo, Táchira, Lara, and especially Mérida, where the Chama river valley between the towns of Ejido and Estanques (Croizat 1954; Bernardi 1956; Costa et al. 2007) constitutes a dry pluviseasonal inland valley, which is, in addi- tion, subjected to a local dry wind known as the “Caldereta” (Bono 1997). This causes a significant drop in precipitation, thus favoring the formation of typical xerophytic vegetation. In this context of local environmental conditions and considering the exis- tence of several other areas in the Americas with similar ecological determinants, it proposes that the flora of this study sites should share a common biogeographic origin with other xerophytic areas in the continent. Graham & Dilcher (1995) and Burnham & Graham (1999) emphasized that the isolation of South America from Central America and Africa during the Tertiary period left its imprint on the flora of the neotropics. In this context, Morrone (2001) notes that the taxa found in the western part of South America are commonly as- signed broad characteristics that connect this area to Australia and New Zealand while those on the eastern side of the continent are assigned general characteristics connecting them to the tropics of the Old World (Morrone 2001). Morrone (1996) separates the western part of South America as the Andean subregion and later places it within the Austral kingdom (Morrone 2001). The rest of South America belongs to the Neotropical region, which also extends to Central America, the An- tilles, and Mexico, where it borders on the Nearctic region (Morrone 2001). On the basis of floristic elements and bioclimatology, Rivas-Martínez et al. (2011b) consider all of South America and the Caribbean to be within the Neotropical-Austroamerican Kingdom, but divided into three subkingdoms. The Neotropical subkingdom, which includes the northern central area of South Phytobiogeography of the species 65 America along with the Caribbean, that is, those regions with a tropical flora and macrobioclimate, whereas the Austroamerican subkingdom includes the south- ern areas with a temperate, mediterranean, and boreal macrobioclimate and flora. Finally, the Circumantartic subkingdom includes the islands and regions arising from the Antarctic with a polar macrobioclimate. The Andes extend lengthwise throughout the two first subkingdoms, with the northernmost regions, the moist highlands (páramos), being included in the Neogranadian region, while the drier highlands (puna) are included in the Tropical South Andean region. The Southern Andes are situated in the Middle Chilean-Patagonian and Valdivean-Magellanian regions of the Austroamerican subkingdom. Prado & Gibbs (1993), Prado (2000) and Pennington et al. (2006) concluded that the present-day dry forests are ves- tiges of a much larger dry formation, the extension of which peaked in the dry and cold climatic period (between 18,000 and 12,000 BP), coinciding with the con- traction of the distribution of wet tropical forests. On the basis of this biogeographic scenario, the aim of this study was to carry out a phytogeographical analysis of the species associated with dry intermountain valleys in the Chama river middle basin in Mérida, Venezuela, evaluating their af- finities with other xerophytic enclaves in the region. MATERIALS AND METHODS Study area Mérida is one state of the Venezuelan Andes (Fig. 1a). Approximately 14% of its surface experiences dry weather, and these areas concentrate 18% of the population of that state (Urbina 2012). This study was conducted specifically in the area between the town of Ejido, in the municipality of Campo Elías, and Es- tanques, in the municipality of Sucre. This state is characterized by a very rugged topography (Fig. 1b). Geographically, the area of Lagunillas is disposed longitudinally along the inner groove of the Andes with a SW-NE orientation (Fig. 1b). This disposition channels the trade winds in the same direction so that they are present as south- westerly winds (Veillon 1989). Bioclimatology The methodology developed by Rivas-Martinez et al. (2011a) was fol- lowed to define the bioclimatic characteristics of the area based on data collected at weather stations in the state of Mérida (Table 1) and compiled by Aranguren (2009) and Aranguren et al. (2012). This data was provided by the Ministry of the Environment and Renewable Natural Resources (http://www.minamb.gob. ve/) and by the National Institute of Meteorology and Hydrology (http://www.in- ameh.gob.ve/) of Venezuela. The thermotypes and ombrotypes were constructed using the world bioclimatic classification system (http://www.globalbioclimatics. org/), found in the section on diagnostics and graphics. Aranguren,