Tropical Andes

José Vicente Rodríguez-Mahecha²⁵, Paul Salaman²⁵, Peter Jørgensen²⁶, Trisha Consiglio²⁶, Eduardo Forno¹⁰⁷, Antonio Telesca¹⁰⁵, Luis Suárez²⁷, Fabio Arjona²⁵, Franklin Rojas¹⁰⁶, Robert Bensted-Smith²⁷ and Victor Hugo Inchausty¹⁰⁷

The Tropical Andes Hotspot is the richest and most diverse biodiversity hotspot on Earth. The Andes Mountain Range, its different cordilleras, its vast array of slopes and peaks, and its isolated valleys provide for a multiplicity of microhabitats and climatic conditions that have led to the evolution of an incredible number of plant and animal species. The hotspot covers a total of 1 542 644 km² in the countries of Venezuela, Colombia, Ecuador, Peru, and Bolivia, and extends a very short distance into extreme northwestern Argentina. The centerpiece of the hotspot is the tropical portion of the Andes mountain chain, which runs north to south in Bolivia, Peru, and Ecuador, then splits into three major cordilleras in Colombia, and extends still further to the northeast into the northwestern corner of Venezuela. The hotspot is bounded roughly by the Tropic of Capricorn to the south and by the natural termini of the Andes to the north in Colombia and Venezuela (including the isolated Sierra Nevada de Santa Marta in Colombia and the Cordillera de la Costa montane forests in Venezuela). The western border of the hotspot is marked by the eastern edge of the Tumbes-Chocó-Magdalena Hotspot, while on the eastern slope of the Andes, in Ecuador, Peru, and Bolivia, the border extends down to 500 m, a realistic cutoff point between the Andean slopes and the Amazonian lowlands. The hotspot is also taken to include the inter-Andean valleys of the northern cordilleras in Colombia.

The Tropical Andes is sometimes divided into northern and southern zones, with the border between them being an arid, east-west valley that coincides roughly with the Ecuador-Peru border in the far northern portion of Peru (Piura) and extending north into neighboring Ecuador. At this nexus, called the Marañón Gap or Huancabamba Depression, altitudes drop to around 500 m, creating one of the most important barriers to faunal and floral migration in the Andes. This gap also serves as an east-west corridor between the Amazon and the Pacific (Gentry, 1977, 1990).

The vegetation of the Tropical Andes Hotspot follows a gradient from lowlands to highlands, with tropical wet and moist forests occurring at 500-1 500 m; cloud forest formations of various kinds, variously referred to as yunga, ceja de selva, or ceja de montaña, which can range in altitude from 800 to 3 500 m (and covering an area of approximately 250 000 km² in Peru alone); and grassland and scrubland systems, which are mainly paramos in the northern Andes and the drier puna in the southern Andes. Both of the latter begin at 3 000 to 3 800 m and extend up to between 4 200 and 4 800 m, usually ending at the snowline. Beginning in the lowlands of the eastern slopes at around 500 m altitude, the sub-Andean forests are similar to those of the hot, Amazonian lowlands, but have fewer palm species, fewer lianas, and fewer buttresses, although the canopy can reach as high as 45 m. Within the sub-Andean forest belt, vegetation begins to transition at around 1 500 m, at which point the plant family Lauraceae becomes the dominant element (Cuatrecasas 1958; Langendoen and Gentry, 1991; Dodson and Gentry, 1991). Andean forests then begin at approximately 2 000 m, and are characterized by shorter trees and more abundant epiphytes such as mosses, lichens, ferns, and algae. At 3 000 to 3 800 m, Andean forests then give way to paramos in the north and puna in the south.

In addition to the main Andean vegetation types, other systems such as dry forests and arid, warm to cool non-forest environments – including woodlands, cactus stands, thornscrub, and matorral – occur adjacent to the wet montane, paramo and puna formations, in dry intermontane basins or along the dry Andean slopes of Peru in particular, usually at altitudes of 2 000 to 3 000 m. Polylepis forests represent another vegetation type unique to the Andes, this tree genus being restricted to the montane areas of western South America, and a conspicuous element of some high-elevation tropical habitats.

In terms of plants and vertebrates, the Tropical Andes Hotspot leads virtually all others in both species diversity and endemism. Perhaps the most impressive figures are those for vascular plants, with an estimated 30 000-35 000 species, or approximately 10% of the world's species, occurring in this hotspot. In fact, the Tropical Andes contains 20%-80% of the total plant species occurring in Bolivia, Ecuador, Peru, and Venezuela. Endemism is equally impressive, with an estimated 50% (and perhaps 60% or higher) of species endemic to the hotspot (around 15 000 species), and peaks in the number of endemic species occurring in the Andean regions of each country (Jørgensen and León-Yánez, 1999; Kessler, 2000, 2002; Van der Werff and Consiglio, 2004). For example, almost 3 000 of Ecuador's 4 000 endemic plant species and around 3 650 of Peru's 5 400 endemic species are Andean; over 25% of total endemic species for Peru and Ecuador occur in the 2 500-3 000-m elevation zone alone. These figures are likely to be an underestimate, especially as new taxa are being described; for example, there have been about 440 plant species described between 1999 and 2003 from the Ecuadorian portion of the Tropical Andes Hotspot alone (out of a total of 532 for the country as a whole) (D. Neill, pers. comm.). In addition, for the Orchidaceae, the largest family in Peru and one that has its peak of endemism in the Tropical Andes, it is estimated that an increase of almost 50% of known species has occurred in the last 10 years (C. Dodson, pers. comm.). It is likely that we need five times the number of plant collections that have been carried out to date to be reasonably certain of the region's plant diversity. Several flagship plant species also occur in the Tropical Andes. Among the list of endemics is a high Andean bromeliad species (Puya raimondii) that takes as long as a century to reach maturity and has the tallest inflorescence of any plant on Earth, reaching as much as six meters in height.

The Tropical Andes also has the highest bird diversity and endemism of any hotspot, perhaps not surprising given that Colombia, Peru, and Ecuador hold the first, second, and fourth positions on the global list of countries with the most avian species. Furthermore, these high numbers of birds derive largely from the Andean portions of these countries (Stotz et al., 1996; Mittermeier et al., 1997). The total number of regularly occurring bird species for the Tropical Andes Hotspot is 1 728, of which an astounding 584 species are endemic. Furthermore, 69 genera are endemic. It is not surprising, then, that BirdLife International recognizes around 21 different Endemic Bird Areas (EBAs) lying partly or entirely within this hotspot, among which the Colombian East Andes, with 34 species endemic, is the most important, having one Extinct (Colombian grebe, Podiceps andinus) and four Critically Endangered species: the gorgeted wood-quail (Odontophorus strophium), chestnut-bellied hummingbird (Amazilia castaneiventris), Niceforo's wren (Thryothorus nicefori), and Colombian mountain grackle (Macrogelaius subalaris). Flagship bird species occurring in this hotspot include the yellow-eared parrot (Ognorhynchus icterotis, CR), an enigmatic macaw-sized species that depends on the Quindío wax palm (Ceroxylon quindiuense, VU), which is the national tree of Colombia; the Andean condor (Vultur gryphus), one of the largest flying birds on Earth; and the diminutive hummingbirds (Trochilidae), a family of tiny, jewel-like birds that reaches its greatest diversity in the Tropical Andes.

Endemism and diversity among amphibians and reptiles in the Tropical Andes exceed even the amazing figures for birds and plants. The Tropical Andes have by far the highest amphibian diversity of any hotspot on Earth, with a total of 1 155 species (1 088 frogs and toads; 28 salamanders, newts and sirens; and 39 caecilians), of which 664 species are endemic. Some of the amphibian genera reach amazing levels of diversity in the Tropical Andes, the best example being the widespread genus Eleutherodactylus of the family Leptodactylidae, with 343 species present and 244 endemic. There are also 10 endemic genera (of the 79 represented). Unfortunately, this is also a hotspot for amphibian extinctions, with several taxa already having disappeared in recent years, particularly some beautiful harlequin toads of the genus Atelopus that tend to be stream-dwelling species and appear highly sensitive to local climate change and habitat loss, and are susceptible to disease (Ron et al., 2003). In terms of reptiles, there are 610 species native to the Tropical Andes Hotspot (304 lizards, 294 snakes, eight turtles and tortoises, and four crocodilians), of which 275 species and three genera are endemic.

Mammal diversity and endemism are also noteworthy. Of a total of 569 species, some 75 are endemic. As elsewhere, rodents are the most diverse mammal group with 220 species, followed by bats with 181 species. There are curious pockets of higher endemism within certain habitats of this hotspot, with both the puna and paramo formations having high mammal endemism. There are also six endemic genera, each represented by single species: Garlepp's mouse (Galenomys garleppi), the Andean rat (Lenoxus apicalis), little or mountain coati (Nasuella olivacea), puna mouse (Punomys lemminus), and fish-eating rat (Anotomys leander, EN), a species known only from the Andes of northern Ecuador and highly specialized for an aquatic existence. The sixth endemic genus is one of the most important mammal flagship species for the Tropical Andes, the yellowtailed woolly monkey (Oreonax flavicauda, CR). It is the largest mammal endemic to Peru, and is only one of three primate genera in the Neotropics to be endemic to a single country. It is restricted to a small area of cloud forest in the northern Peruvian departments of Amazonas and San Martín. Other important large mammal flagships include the spectacled bear (Tremarctos ornatus, VU), woolly or mountain tapir (Tapirus pinchaque, EN), and vicuña (Vicugna vicugna), a camelid that lives at altitudes of 3 000 to 4 800 m, mainly in the puna ecosystem.

Freshwater fishes are represented by 380 documented species, although many more are expected as explorations extend onto the Amazonian flanks of the mountains. A total of 131 fish species are endemic to the hotspot, a surprising number for an area centered on the crest of a mountain range. One major component of endemism consists of members of the cyprinodont genus Orestias, which has undergone a significant radiation in Lake Titicaca and nearby drainages, resulting in a cluster of 43 species endemic to the southern end of the hotspot. Most remarkable perhaps are the naked sucker-mouth catfishes (family Astroblepidae) that inhabit torrential streams from one end of the hotspot to the other. With the exception of a species in Panama and a few species that extend to lower elevations, the family's 90 species are endemic to the region.

Humans have lived in the Andes for many millennia, and the region was home to one of the world's great past civilizations, the Empire of the Incas. However, the degree of human impact varies considerably within this region, from areas that have lost almost all of their original vegetation (e.g., some of the inter-Andean valleys in Colombia and Ecuador) to some that are still largely pristine (e.g., parts of the eastern slopes of the Andes in Bolivia and Peru). Broadly speaking, the most disturbed portions of the hotspot are the dry inter-Andean valleys, where the original forests have largely disappeared and, on average, less than 10% remains. The inter-Andean valleys provide the most hospitable environment for humans in the region, and these areas have been densely populated since pre-Columbian times.

Other heavily impacted ecosystems within the Andes are the paramos and the puna. Both have been greatly modified by seasonal burning and grazing, agriculture, and mining. The puna also suffers from over-exploitation of certain slow-growing woody plant species for firewood, especially around urban centers such as Arequipa, while puna ecosystems of both Peru and Bolivia are also affected by the mining industry, with toxic runoff and water contamination being a major concern.

An additional threat that has emerged in recent years, especially in the high Andean forests of Colombia, is the cultivation of the opium poppy, in clearings cut within montane forests to grow this highly profitable illegal crop. Unfortunately, the programs designed to control illegal crops use chemical defoliants that cause even more damage to biodiversity, as well as allowing harmful chemical herbicides to enter into highland ecosystems and trickle into lower altitudes through the rivers and streams, a factor that may have contributed to amphibian and freshwater fish die-offs in these regions.

As a result of all these pressures, a large portion of the natural vegetation of the Tropical Andes Hotspot has already been lost, and it is estimated that the area remaining in fully intact condition is likely no more than 25%, or 385 661 km², and probably much less. The eastern slopes of the Andes in Peru and Bolivia have the most extensive areas of largely intact natural vegetation.

Despite the bleak picture painted above, protected areas today are conserving some of the most important remnants of the Tropical Andes Hotspot. In total, these protected areas cover some 16% of its original extent. However, many of these protected areas are small and ineffective, and only 7.9% of the hotspot is protected in reserves or parks in IUCN categories I to IV. This has led to the recognition for the need not only to create new and better-managed parks, but also to interconnect existing parks through what are commonly referred to as “corridors.” An example of a “corridor” project, and a model for using corridors as a conservation strategy in the Andean region, can be found in the Amazon-Andes interface in southern Peru and adjacent portions of Bolivia. One of the first and most important components of this corridor is Manú, the largest rainforest biosphere reserve on Earth at 18 812 km², and which protects major areas of puna, cloud forest, and lowland forest. Another major piece of this string-of-pearls of Andean slope ecosystems is the Tambopata-Madidi protected area complex straddling the Peru-Bolivia border, representing fully 22 250 km² of new parks created in the richest portion of the most diverse biodiversity hotspot on Earth, an area larger than El Salvador and a very significant accomplishment for biodiversity conservation.

The Tropical Andes has benefited from a series of major conservation investments in the last several years. For example, the Critical Ecosystem Partnership Fund has made a commitment to invest some $6 million in the Vilcabamba-Amboró Corridor in Peru and Ecuador over the past three years, with the specific objective of building civil society capacity to carry out biodiversity conservation activities in this important region. At the same time, the Global Conservation Fund (GCF), based at Conservation International, has invested $1.273 million in projects in Bolivia, Colombia, Peru, and Ecuador. These projects have helped to stimulate the creation of some nearly 3 million hectares of new protected areas in some of the highestpriority regions of these countries. Included among the projects supported by the GCF were two debt-fornature swaps in Peru in 2003 and in Colombia in 2004. Both of these were carried out in partnership with the World Wildlife Fund, The Nature Conservancy, and the United States Government; they will provide $10.6 million to 10 sites in Peru and $10 million to five sites in Colombia over a 12-year period. These are just a few examples of the direct support given to conservation in recent years.

Other conservation activities in the region are focusing directly on amelioration of some of the most dangerous threats to the environment, e.g., infrastructure development, while several on-the-ground efforts to conserve key threatened species (such as the recent recovery of the yellow-eared parrot) are also under way. In conclusion, looking at this region as a whole, there is considerable room for optimism. Although portions of the Tropical Andes have been heavily impacted, extinctions have been relatively few, and there is still enough time to design and implement conservation areas at a scale which is likely to ensure the survival of the vast majority of life-forms that exist in this, the richest of the planet's terrestrial hotspots.

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