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Flora, vegetation and ecology in the Venezuelan Andes: a case study of Ramal
de Guaramacal
Cuello Alvarado, N.L.
Publication date
2010
Link to publication
Citation for published version (APA):
Cuello Alvarado, N. L. (2010). Flora, vegetation and ecology in the Venezuelan Andes: a case
study of Ramal de Guaramacal. Universiteit van Amsterdam, Institute for Biodiversity and
Ecosystem Dynamics (IBED).
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Chapter 1
Introduction
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1.1 INTRODUCTION
The Venezuelan Andes belongs to the northernmost bioregion of the Andes. With regard to biodiversity this area represents one of the most prominent areas on a global scale. At a regional scale it is one of the zones with highest priority for conservation (Dinerstein et al. 1995; Mittermeier et al. 1999; Myers et al. 2000). The Andes of Venezuela is a continuation of the Colombian Cordillera Oriental which ends at the Táchira Depression on the Colombian-Venezuelan border. The northern extension is a small range, the Serranía de Perijá. The northeastern extension is the Cordillera de Mérida, mainly referred to as the Venezuelan Andes, and, includes the Páramo de Tamá which is part of the Cordillera Oriental. Another mountain system, the Coastal Cordillera of Venezuela, is considered as a system separated from the Andes (Schubert 1980; González de Juana et al. 1980; Pouyllau 1989; Vivas 1992).
The Cordillera de Mérida is composed of several ranges including the Sierra Nevada de Mérida, Sierra de la Culata, Sierra de Santo Domingo, Sierra de Tovar, Sierra de Uribante, and the Sierra de Trujillo. This complex of ranges is about 100 km wide and extends in northeastern direction over 450 km. The highest altitude is reached at the Pico Bolívar (5007 m) in the Sierra Nevada de Mérida. Most of the Cordillera de Mérida is covered by montane forest while the land over 3000 m, at places even over 2500 m, is covered by páramo.
During the past two decades the significant taxonomic and ecological diversity of the northern Andes, as well as the ecological importance of these mountain ecosystems, has been recognized (Van der Hammen et al. 1983, 1986, 1989, 2003, 2005, 2008; Henderson et al. 1991; Ramsay 1992; Churchill et al. 1995; Gentry 1995; Luteyn & Churchill 2000; Rangel 2000a, 2000b, 2007; Kappelle & Brown 2001; Lauer et al. 2001; Young et al. 2002; Beck et al. 2008; Gradstein et al. 2008). However, the number of studies on biodiversity of Venezuelan mountain ecosystems, particularly of montane forests, are limited (Ataroff 2001). The botanical knowledge of the Venezuelan Andes is still low (Olson et al. 1997; Dorr et al. 2000) compared to other areas, such as the Guayana Tepuis. The Tepuis area has been always attractive for botanical exploration and there we find the greatest efforts of botanical knowledge (Huber 1995) and the nine volumes of the Flora of the Venezuelan Guayana (Steyermark et al. 1995).
Most studies on the flora and vegetation of the Venezuelan Andes have been carried out in the State of Mérida. Pionering studies are those of the forests of La Mucuy (Lamprecht 1954) and of La Carbonera (Veillon 1965). Classic studies on the páramo vegetation are the ‘Flora de los Páramos de Venezuela’ by Vareschi (1970) and the ecological studies on páramos by Monasterio and collaborators (Monasterio 1980).
Recent floristic analysis in the Venezuelan Andes of montane forest (Kelly et al. 1994, 2004; Schneider et al. 2000; Schneider 2001) and páramos (Yánez 1998; Berg 1998; Berg & Suchi 2000) are restricted to local areas or preliminary (Ortega et al. 1987; Cuello 1996, 1999, 2002; Dorr et al. 2000). More comprehensive studies of the flora and vegetation of larger areas, including phytogeographical analyses of páramo flora are few (Bono 1996; Ricardi et al. 1997, 2000) and 3 Introduction
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floristic lists are up to date limited to the flowering plants of the páramo (Briceño & Morillo 2002, 2006).The scarcity of information on the floristic composition of the Andean ecosystems of Venezuela is hindering a good estimation of the floristic diversity, the botanical composition of most forests and páramos, and the status of conservation of the endemic flora in the protected areas. In the Mérida Andes mostly dry páramos have been studied, but almost no knowledge is available for bamboo páramos. The descriptions of the different páramo and high Andean forest communities by Monasterio (1980) provide a first overview. Phytosociological studies describing associations and higher syntaxonomical units are only known for the high Sierra Nevada de Mérida páramos (Berg 1998) and for the transect study in the Andean and high Andean forests (Schneider 2001).
These phytosociological studies triggered our interest to learn more about the montane forest and páramo under wet climatic conditions in the Cordillera de Mérida. Studies on the wet Andean ecosystems has been carried out before in Colombia (Van der Hammen et al. 1984, 2005, 2008; Rangel Ch. & Lozano C. 1986; Rangel Ch. 1994; Cleef 1981) where bamboo páramos were described for the first time.
As is the case in other South American countries, the Venezuelan Andes are suffering an increased human intervention and many forests and páramos have been converted into agricultural land. The conversion of areas with montane forest into pasture land is a common feature in the Venezuelan Andes. This practice is changing the water flows and erosive processes in the uplands, affecting dramatically soil stability, and the supply of water to people both in the upland and lowland areas (Ataroff 2001).
Fortunately, a relatively large part of the montane forests and páramo ecosystems in the Venezuelan Andes are preserved by a net of thirteen national parks that in total cover about 31% of the whole mountain system. One of such protected areas is Ramal de Guaramacal, located at the northeastern end of the Venezuelan Andes. It lies within the Guaramacal National Park and strong human intervention is not present. The Páramo of Guaramacal has been reported as an important center of diversification of the Espeletiinae genus Ruilopezia (Cuatrecasas 1986). Moreover, due to its relative isolation, Ramal de Guaramacal is also an area with an endemic flora (Steyermark 1979; Ortega et al. 1987; Dorr et al. 2000).
The presence of a road traversing the Guaramacal range from the drier northwestern slope (Andes-facing) to the moister southeastern (llanos-facing) slopes at lower elevation, offered an excellent opportunity to initiate in 1995 a research project to study floristically the vegetation along an altitudinal gradient. It has been widely recognized that altitudinal gradients in mountain ecosystems have considerable impact on the distribution of biodiversity. Altitudinal gradients in temperature, precipitation, and other parameters are known to influence vegetation and diversity patterns over relatively short distances (Whittaker 1960; Gentry 1982, 1988, 1995; Lomolino 2001). Temperature can be the principal driver of ecosystem functioning (Chapin & Körner 1995; Colwell et al. 2008; Svenning & Condit 2008).
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With support from the related project Flora of Guaramacal, jointly conducted by Basil Stergios (UNELLEZ) and Laurence Dorr (NMNH of Smithsonian Institution), the current project combined geobotanical exploration and floristic surveys of the vegetation types. The aim was to explore the structure, botanical composition, and the diversity of forests and páramo, and to relate these results to environmental gradients. A specific goal was to examine the relationship between altitudinal patterns of diversity and plant functional traits, particularly in the montane rain forests. In addition, the phytogeographical patterns of the wet páramo flora were elucidated and compared to páramo areas in Ecuador, Colombia, and the Talamancas of Central America. The results of this study are basic for conservation and biodiversity management in the region.The study of vegetation along the altitudinal gradient in Ramal de Guaramacal was done using a floristic, phytosociological and a plant functional approach. A growing amount of literature is illustrating the value of functional approaches to understand biodiversity, pointing out the importance of analyzing changes of functional traits along an altitudinal gradient for predicting the effects of environmental changes on ecosystem functioning, such as those induced land use, cover changes or by global warming (Díaz & Cabido 1998; Díaz et al. 1999; Duckworth et al. 2000; Lavorel & Garnier 2002; McGill et al. 2006). Recently, some studies focused on the importance of traits associated with animal-plant interactions to analyse the relationship between species diversity and functional diversity with the aim to explore the ecosystem responses to environmental change, e.g. caused by deforestation (Mayfield et al. 2005) and fragmentation (Girao et al. 2007). In mountain ecosystems it is expected that with increasing elevation temperature and available land surface decrease leading to more environmental stress and more ecological filtering as a consequence (Mayfield et al. 2005). In this study, the change of composition and diversity of some functional (energy balance-related, reproductive/fragmentation-related) traits of undisturbed mountain forest of Ramal de Guaramacal was analyzed along an altitudinal gradient with the aim to contribute with benchmark information to studies of degraded tropical Andean ecosystems (see Chapter 6).
Several topics on the diversity of flora and vegetation ecology of Ramal de Guaramacal along altitudinal gradients have been addressed, including issues of phytosociology, altitudinal zonation, floristic diversity, phytogeography and functional diversity. The observed patterns were interpreted on the basis of comparisons with other regional and extra-regional studies.
This Ph.D. thesis consists of several published articles and manuscripts in review at international journals.
Chapter 2 includes the characterization of the physical environment of the study
area of Ramal de Guaramacal and gives an overview of the geobotanical exploration and botanical research conducted there. This information serves as reference information for all chapters. This chapter gives a description of the floristic diversity and structure of the montane rain forest vegetation of Ramal de Guaramacal and presents a syntaxonomic scheme to classify the montane rain forests of this part of the Venezuelan Andes. It is based on quantitative data and analysis of physiognomy, floristic composition, ecological relations, and spatial 5 Introduction
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distribution of the different vegetation communities. An altitudinal zonation is presented and a comparison is made to montane forests elsewhere in the Venezuelan Andes. Finally human influence and issues of conservation are discussed.Chapters 3 and 4 deal with the study of the wet bamboo páramo vegetation on top
of the Guaramacal mountain range. Chusquea dominated bamboo páramos are distributed along the humid upper forest line on the Llanos facing slopes of the Venezuelan Andes. In Venezuela this type of vegetation was not studied before.
Chapter 3 covers the phytosociological classification and description of zonal
páramo vegetation communities and examines the affinities to páramo vegetation elsewhere in the tropical Andes. In this chapter we also address the mosaic-like distribution of shrub páramo, grass páramo and dwarf forest vegetation communities which are present on the summits of Ramal de Guaramacal. These aspects are based on the analysis of physiognomy, composition, floristic diversity, and relationships of the vegetation communities and the environmental variables involved.
Chapter 4 comprises the classification of azonal wet páramo vegetation
communities found so far in páramo areas of Ramal de Guaramacal. Patches of azonal bunchgrass, Sphagnum bogs, aquatic communities, and boggy bamboo páramo are described and their floristic relationships with similar páramo communities elsewhere in Colombia and Venezuela are discussed.
Chapter 5 is an introduction to the analysis of the phytogeographical patterns and
affinities of the lowermost and the wet páramo vegetation of Ramal de Guaramacal. It provides an analysis of the floristic connections with the neighboring dry páramos of the Sierra Nevada de Mérida, and the floras of other páramo areas in the northern Andes and in Central America. We describe how phytogeographical components change among different páramos. Using ordinations, we explored whether the phytogeographical patterns of the páramo flora of Ramal de Guaramacal are determined by temperature, or more by the overall permanent humidity which characterizes the Guaramacal bamboo páramo.
Chapter 6 encompasses the analysis of functional diversity of the mountain forest
of Ramal de Guaramacal as a function of altitude. This study is based on the vascular plant species composition of forest plots sampled along an altitudinal gradient in the study area (chapter 2) and their linked functional traits related to energy balance and fragmentation, obtained by means of literature and herbarium studies. Using DCA ordination and Fourthcorner analysis, we explored the relationships between the studied traits and environment and discuss the implications of climate change in temperature on functional changes. This study shows the advantage of functional approach above species approach for the analysis of the effect of environmental changes on mountain forest ecosystems. Finally, a synthesis of the results and conclusions based on all chapters are presented in chapter 7.
