Biogeografía

 

The orchid flora of the Colombian Department of Valle del Cauca

 

La orquideoflora del departamento colombiano de Valle del Cauca

 

Marta Kolanowska*

 

Department of Plant Taxonomy and Nature Conservation, University of Gdańsk. Wita Stwosza 59, 80-308 Gdańsk, Poland. * martakolanowska@wp.pl

 

Recibido: 30 julio 2012
Aceptado: 15 noviembre 2013

 

Abstract

The floristic, geographical and ecological analysis of the orchid flora of the department of Valle del Cauca are presented. The study area is located in the southwestern Colombia and it covers about 22 140 km² of land across 4 physiographic units. All analysis are based on the fieldwork and on the revision of the herbarium material. A list of 572 orchid species occurring in the department of Valle del Cauca is presented. Two species, Arundina graminifolia and Vanilla planifolia, are non-native elements of the studied orchid flora. The greatest species diversity is observed in the montane regions of the study area, especially in wet montane forest. The department of Valle del Cauca is characterized by the high level of endemism and domination of the transitional elements within the studied flora. The main problems encountered during the research are discussed in the context of tropical floristic studies.

Key words: biodiversity, ecology, distribution, Orchidaceae.

 

Resumen

Se presentan los resultados de los estudios geográfico, ecológico y florístico de la orquideoflora del departamento colombiano del Valle del Cauca. El área de estudio está ubicada al suroccidente de Colombia y cubre aproximadamente 22 140 km² de tierra a través de 4 unidades fisiográficas. Todos los análisis aquí presentados se llevaron a cabo basándose en trabajo de campo y en la revisión de material de herbario. Se presenta la lista de las 572 especies de orquídeas que se presentan en el departamento de Valle del Cauca. Dos de ellas, Arundina graminifolia y Vanilla planifolia, son elementos no nativos de la flora de orquídeas estudiada. La mayor diversidad de especies se observa en las regiones montañosas de la zona de estudio, sobre todo en los bosques montanos húmedos. El departamento de Valle del Cauca se caracteriza por el alto nivel de endemismo y la dominancia de elementos de transición en la flora estudiada. Los principales problemas encontrados durante la investigación se discuten en el contexto de los estudios florísticos tropicales.

Palabras clave: biodiversidad, ecología, distribución, Orchidaceae.

 

Introduction

The vast majority of plant species are concentrated in the tropical and sub-tropical regions of the world. One of the most important tasks for the scientists today is to describe the biodiversity of these areas, in which the researchers face the interactions of environmental, economic and social problems.

The Republic of Colombia, containing about 10% of the known species in the world, is one of the most biodiverse countries on Earth. Nearly 30% of the vascular plants occurring in Colombia are endemic. Unfortunately, the economic and social problems associated with development in the last 2 decades has resulted in a noticeable habitat loss and the threat of the national biodiversity.

The extraordinary flora of the Colombian vascular plants accounts for over 24 000 species with the best representation observed within the Orchidaceae family (Jørgensen et al., 2011). Previous work by Ortiz and Uribe (2007) included over 3 200 species and 4 years later this number was elevated to over 3 500 by Jørgensen et al. (2011). Unfortunately, only the orchid flora of the department of Antioquia has been catalogued so far (Idárraga-Piedrahita et al., 2011).

The aim of the present study was to prepare a complete catalog of Orchidaceae occurring in the department of Valle del Cauca, which is one of the most poorly floristically known regions of Colombia, encompassing at the same time 4 important physiographic units.

The department of Valle del Cauca occupies about 22 140 km² in southwestern Colombia (Fig. 1) constituting about 2% of the country's territory. It extends from the Pacific lowlands across the Western Cordillera and the valley of the upper Cauca river to the western slope of the Central Cordillera (3°05'-5°01' N, 75°42'-77°33' W). The natural limits of the department are the Pacific Ocean on West and the Cauca River on the South. It is bordered by the departments of Caldas and Risaralda in the North, Chocó in the North-West, Quindio and Tolima in the North-East and Cauca in the South (Bolívar et al., 2004).

In the study area 4 physiographic units are present: the Pacific Plate, the Western Cordillera, the Valley of Cauca River, and the western flank of the Central Cordillera. This physiographic diversity is reflected in a wide variety of environmental conditions. According to the Etters' map (1998), 18 different ecosystems occur in the department of Valle del Cauca –10 natural and 8 transformed. The most widespread are: sub Andean humid forest (bosque húmedo subandino), which covers about 7.6% of the area, high-montane humid forest (bosque altoandino húmedo), and cloud forest (bosque de niebla) occupying about 6.6% of the department (Bolívar et al., 2004).

The most important ecosystems for biodiversity are paramo, sub Andean and Andean forests, dry tropical forest and tropical very dry and sub xerophytic forests, wetlands, tropical wet forests and flooded forests.The variety of ecosystems and natural habitats have resulted in a great diversity of species in the study area. Unfortunately, the flora of this region has been very poorly studied.

 

Material and methods

The information about orchid species documented in the department of Valle del Cauca, their distribution in the study area, their geographical and altitudinal range, and the habitat requirements were obtained during the fieldwork, and the revision of herbarium material. All information was complemented by data obtained from the literature, mostly protologues and Neotropical orchid floras (i.a. Garay 1978; Hamer, 1988, 1990; Hágsater and Salazar, 1990; Hágsater and Sánchez Saldaña 2001, 2004, 2006, 2007, 2008, 2009, 2010; Hágsater and Soto Arenas 2003, 2008; Dodson and Luer 2005, 2009, 2010) and the electronic database provided by the herbarium AMO.

Herbarium specimens were examined according to the standard procedures. Every studied sheet was photographed and the data were taken from the labels. Both vegetative and reproductive characters of each plant were studied. In total 3 576 dried specimens and 76 flowers preserved in alcohol stored in AMES, AMO, COL, CUVC, K, MO, P, S, UGDA, VALLE and W were examined. Herbarium acronyms follow Index Herbariorum (Thiers, continuously updated).

The fieldwork in the department of Valle del Cauca was conducted during 4 expeditions between 2009 and 2011. The objective of the excursions was to collect the geolocation data and information about the type of habitat in which orchid populations occur. The habitats were classified according to the Espinal and Montenegro (1980) system, based on the presence of the characteristic taxa defined by Cuatrecasas (1958) and Bolívar et al. (2004).

The data gathered on species distribution and elevation range were used to define directional and altitudinal elements within orchid flora of the department of Valle del Cauca. The directional elements were defined based on the general geographical range of each species, the species which geographical range do not have limits in the study area were classified as transitional elements, and those with a limited distribution in the department of Valle del Cauca as southern (northern range limit), northern (southern range limit) or western (east range or eastern (western range limit) elements, according to their distribution. Each species was classified in one of 6 categories based on the vertical distribution of its populations and that was the basis for defining the altitudinal elements: lowland (below 300 m), upland (300-700 m), premontane (700-1 200 m), montane (1 200-2 500 m), high-montane (2 500-3 400 m) and paramo (above 3 400 m). The elevation limits are related to
the vertical distribution of the habitats in the study area.

 

Results

Orchid species richness and taxonomic diversity. This study confirmed the occurrence of 572 orchid species in the department of Valle del Cauca, including the description of 6 new taxa. Previous information on the occurrence of 48 species was incorrect being the result of the misidentification of herbarium material or incorrect interpretation of the locality given on the herbarium sheet label. Neither fieldwork nor examination of dried specimens could confirm the occurrence of 17 orchid species previously reported from the study area, i.a. information given in "Libro Rojo de las plantas en Colombia vol. 6" (Calderón, 2007), without herbarium reference material.

The Orchidaceae of the study area constitute about 16% of the Colombian orchid flora estimated by Ortiz and Uribe (2007) as 3 497 species (Appendix, Fig. 2). From all 133 genera, nearly 45% are represented by a single species - this group embraces also 4 monotypic genera: Frondaria Luer, Gerlachia Szlach., Soterosanthus F. Lehm. ex Jenny and Trizeuxis Lindl. The richest genus, with 121 species, 8 of which are endemic to the study area is Epidendrum L.

According to the classification system of Chase et al. (2003), with later changes (Bateman et al. 2003), the vast majority of Orchidaceae occurring in the study area belong to the subfamily Epidendroideae (91%), represented mainly by the tribe Epidendreae (64%). Within those taxa, most of the species belong to the subtribe Pleurothallidinae (24 genera, 195 species) and Laeliinae (7 genera, 143 species; Appendix).

Distribution patterns. Information on the vertical distribution of 22 species occurring in the department of Valle del Cauca is not provided. For all other orchids, the altitudinal distribution and the vertical range in the study area have been determined. Almost all species listed are native to Colombia and only 2: Arundina graminifolia (D.Don) Hochr. and Vanilla planifolia Jacks. ex Andrews were found as invasive in the zone.

The highest species diversity is observed in the montane regions (1 200-2 500 m alt.), where populations of 347 (60%) species have been documented. Simultaneously, 63% of these (218 species) do not occur in the lowlands and/or in the high-montane and paramo areas. Both the lowlands and high-montane areas are characterized by a low orchid diversity –only 85 (15%) species were reported from altitudes below 300 m and only 24 (4%) from higher elevations above 3 400 m.

The determination of the vertical range of 548 species, for which sufficient data were gathered, allowed for the determination of 333 altitudinal elements within the orchid flora (Appendix). The best representation is observed among montane species, which constitute 38% of the Orchidaceae (218 species) occurring in the department of Valle del Cauca. Contribution of other elements is comparatively insignificant. Only 36 (6%) of species are associated with the lowland regions, 7 with uplands (1.2%), 39 (6.8%) with premontane areas, 23 with high mountains (4%) and 10 species (1.7%) with paramo. About 3.7% of the orchids (215 species) are characterized by a wide vertical
range.

The gathered data allowed the determination of the general geographical range of 543 (94%) of the orchid species occurring in the department of Valle del Cauca (Appendix). The endemic and invasive species were excluded from the analysis of the directional elements. Almost 70% (325 species) do not reach the limit of their range in the study area, hereby these are transitional elements. The distribution of 29 (0.6%) species is related with the Andes which are eastern elements. The western elements include 29 species (0.6%) which range extends for a few kilometers from the coastal zone of the Pacific. Thirty-five species (7.5%) were classified as northern, and 49 as southern elements (10%).

The level of endemism observed is extremely high (Appendix). The localities of 74 species (almost 13%) are known exclusively from the study area. Most of the endemic taxa belong to the subtribes Pleurothallidinae and Laeliinae (tribe Epidendreae).

Ecological analysis. The orchid flora of the department of Valle del Cauca is dominated by the epiphytes (83.2%, 476 species) –most of them (400 species) are holoepiphytic. Only 15% of species occurring in the study area are lithophytic (4 obligatory) or terrestrial (81 obligatory) and exclusively 3 species of the genus Vanilla were reported growing as vines. The variability of the plant habit was observed within the populations of 87 (15%) species.

The suitable habitats were determined for 95% orchids reported from the department of Valle del Cauca. Two species, Arundina graminifolia and Vanilla planifolia, have been excluded from the analysis, as they are non-native species in the study area and their long-time persistence in the department is unsure.

Within the natural habitats, the greatest diversity of orchid species was observed in wet montane forests with 225 species (nearly 40% of the orchid flora of the department of Valle del Cauca). In moist premontane forest, which is the most widely spread habitat in the study area, 171 species (30%) were found. On the other hand, mangroves show the poorest orchid flora with only 6 species (less than 1.5%) recorded. Only 2% of Orchidaceae are related with the open areas of disturbed montane and premontane forests. Another 15 species are associated with exposed, steep slopes –both rocky and grassy.

The occurrence of 14 Orchidaceae species was reported from the areas of orchards. Most of them were found in abandoned cocoa plantations. A smaller number of taxa are related to Coffea and Citrus orchards. In the tea (Camellia) and rubber (Hevea) plantations the occurrence of a single species was recorded (Table 1).

 

Discussion

As mentioned before, a complete list of orchid species has been compiled only for the department of Antioquia. As the territory of this administrative unit is much larger (over 63 000 km²) than the department of Valle del Cauca and it is located within completely different physiographic units (eg. Carribean coast, Darién gap) it is not comparable with the studied area. Noteworthy is that in the department of Antioquia there is a high level of endemism within the orchid flora –over 25% of Orchidaceae is known exclusively from this region (Idárraga-Piedrahita et al., 2011).

No data exists on the orchid species richness of other Colombian physiographic or administrative units. So far studies on Orchidaceae has been conducted in relatively small areas (e.g. Kolanowska et al. 2011; Misas Urreta, 2005, Santa Jiménez et al., 2009). Since the floral composition, as well as biogeographical and ecological aspects of Colombian orchid flora are still poorly recognized, the necessity to intensify the comprehensive research is unquestionable.

The geological history and current habitat continuity observed in the equatorial direction, make the Pacific region and the Andes dispersal routes for many orchid species. The department of Valle del Cauca, which embraces both the Pacific lowlands and the chains of the Western and Central Cordilleras, is therefore a region rich in transitional taxa originating from both Central America and the central part of South America.

Our results confirme the information regarding the concentration of Orchidaceae in the montane areas (Vareschi, 1976). In the study area the occurrence of about 70% (391 species) of orchids was observed above 1 200 m altitude, while in the lowlands and uplands only 104 species were recorded. Moreover, only 10 endemic species were found below 700 m altitude.

The greatest threat to the existing orchid populations is the increase in agricultural areas, mainly sugar cane crops and pasturelands. Due to the intensive logging of tropical dry forests which began in the 1960's (Bolívar et al., 2004), the poorest Orchid flora is now observed within the valley of Cauca river area.

Orchid flora of the department of Valle del Cauca, which covers less than 2% of the Colombia's territory, is extremely rich –572 species found in the study area represent about 16% of the national Orchid Flora. At the same time, the observed level of endemism is very high (13%). However, there is a huge possibility that the actual number of orchid species occurring in the Republic of Colombia is much higher than the numbers that appear in the previously published studies (eg. Ortiz and Uribe, 2007).

The number of field studies conducted in Colombia is very limited, even if it seems that the financial resources allocated in nature conservation, including research, are not directly related to this fact (Galán and Canal, 2002). The scarce number of field studies seems to be connected with 2 other factors. The first one is the specificity of the tropical vegetation - many regions of Colombia are basically inaccessible to scientists because of the complete lack of communication routes, or to temporarily cutting off those areas from the nearest human settlements. In the department of Valle del Cauca the problem is noticeable in the southern part of the Buenaventura district, which is almost completely devoid of terrestrial roads. Getting into many regions of this area in the rainy season is not possible due to the high water levels in the rivers, which intersect the entire territory of the district. On the other hand, the terrorist and drug cartel threat is still high in many Colombian regions. The most dangerous areas, in this aspect, are the high-montane areas of the Western Cordillera. In the department of Valle del Cauca, field studies are not conducted for safety reasons (paramilitary threats), i.e. in the Páramo de Bavaya (Central Cordillera), where the last floristic studies were conducted in 1946 by José Cuatrecasas.

This limited fieldwork results in insufficient floristic documentation of the tropical regions, hence the results of the research based only on herbarium material revision seems to not reflect the entire diversity of Colombian plant species, including orchids. For the same reason, the geographical ranges of taxa may be underestimated, or seem to be disjunct.

Another issue is the correct identification of the herbarium material. The errors in the determination of specimens results in copying from the available literature false information about the number and the distribution of many taxa. Within the herbarium material collected in the department of Valle del Cauca many errors of identification were uncovered among specimens representing 23 species of Orchidaceae.

 

Acknowledgements

I would like to express my sincere gratitude to Oscar Alejandro Pérez Escobar and Edicson Parra Sánchez for their accompaniment during the field studies. I am grateful to Eric Hágsater, Carlyle A. Luer and Pedro Ortiz for their cooperation during the research. The curators and staff of the cited herbaria are thanked for their kind hospitality and assistance during the visits. The research described here has been supported by the grant from the Polish Ministry of Science and Higher Education (project No. N N304 043939).

 

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