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Tropical Dry Forest of Costa Rica

A biodiversity specially adapted to the seasonal drought

Tropical Dry Forest of Costa Rica. See more pictures in Gallery. Black Iguana. See more Tropical Dry Forest pictures.  The Tropical Dry Forest is the most threatened terrestrial environment in Costa Rica, and one of the most scarce in Central America (1), which is not a surprise because of its main feature, as being located in a tropical region with seasonal rainfalls, this results in several months of severe drought; indeed it exhibits the most greatest rate of days with no rain along the year in Costa Rica. This implies directly that all the tropical dry forest plants and animals inhabiting there had been developed the proper evolutive adaptations to fit with the conditions of an availability of nutrients and water very much less than rainforest: This obligates plants to lose their leaves during the dry season, and animals to require big territories. Besides it must be confronted the occurrence of human provoked fires precisely and unfortunately in the most dry and hot period.

Tropical Dry Forest of Costa Rica is by all of this a delicate life zone that requires for its conservancy the protection of wide and continuous areas for the survival of large mammals, specially the predators because they are at the top of the food chain. A large part of this forest, at the NW region of Guanacaste is protected into the Área de Conservación Guanacaste, but it is needed even more. It must be cared for its great vulnerability intrinsic by its nature to the human actions, which have the duty of protect the few that remains of it and try to restore as much as possible.

For a practical approach, the Tropical Dry Forest Biome can be considered as equivalent to the Tropical Dry Forest Holdridge Life Zone (bs-T) as well as its transition.

(En Español: Bosque Tropical Seco de Costa Rica)

Distribution Map for Costa Rica Tropical Dry Forest Costa Rica Tropical Dry Forest Facts
Synonyms: Neotropic Seasonal Forest, Tropical Seasonal Forest, Tropical Deciduous Forest.
Distribution: Surrounding the Gulf of Nicoya and along the pacific seashore of Peninsula of Nicoya (See map →).
Current Weather: Early Dry Season.
Availability of resources: Restrictive.
Threats: Deforestation, human fires, loss of territory by unsustainable human development, pollution, animal hunting and capture.
Experience it!: Tropical dry forest surroundings and trails while staying at La Norma Ecolodge (Santa Cruz, Guanacaste), felines & wildlife at Las Pumas Wildlife Rescue Shelter (Cañas, Guanacaste). Conservancy guidelines: Take extreme care in avoid and keep under control any fire possibility (obviously the dryness makes the combustion too easy), ensure the proper dispose of wastes, do not feed wild animals and DO NOT take out animals nor plants from their natural environment.
Parameters as Holdridge Life Zone:.
     Key: bs-T
     Area: 5,263 Km²; 10.3% of country (2).
     Altitude: 0-600 m ASL (1,968.5 feet).
     Rainfall: 1,100-1,500 mm/year. (3)
     Temperature: Max: 91.4ºF (33ºC), Min: 71.6ºF (22ºC) (Annual averages). (3)
     Dry Season: 6 - 8 months.
     Canopy Height: 20-30 m.
     Vegetation: Deciduous.
     Forest Layers: 4 (2 of trees).
     Concentration: Low density.
     Epiphytes: Scarce.
Features & Facts:

  • The drought in the dry season is caused by the Trade Winds which comes fron NW, and start to manifest in November (causing at this month the transition from the rainy season).
  • The restrictive conditions have provided the selective pressures for the evolution of highly distinctive vegetative forms.
  • Deciduous vegetation (falling of leves in the dry season) as adaption to avoid of water by transpiration through each leaf.
  • Have four layers: 2 tree layers (canopy and understorey), the shrub layer and the ground layer.
  • In the Tropical Dry Forest the rainfall period is a really rainy one, even more intense than in rainforests. The drought dried springs become full with strong flows.
  • During the last two decades it has been achieved an amazing recovery process of the tropical dry forest in the province of Guanacaste, which must be kept. (4)
  • The year 2011 has been declared the International Year of Forests by the United Nations.

Howler Monkey (Alouatta palliata) family at the Tropical Dry Forest of Costa Rica (La Norma Ecolodge, Guanacaste). Black Iguana (Ctenosaura similis) taking the plenty solar energy thanks to the lack of leaves. (La Norma Ecolodge, Guanacaste). The White-throated Magpie-Jay (Calocitta formosa) is a bird whose habitat is the dry forest exclusively. (La Norma Ecolodge, Guanacaste). Male Howler Monkey (Alouatta palliata) fixed with its prehensile tail, in this overall deciduous forest. (La Norma Ecolodge, Guanacaste). Howler monkeys (Alouatta palliata) roving through the tree branches in the dry season. (La Norma Ecolodge, Guanacaste). "Cortés Amarillo" tree (Tabebuia ochracea), is a feature of the Tropical Dry Forest. (La Norma Ecolodge, Guanacaste). Acacia ants (Pseudomirmex spp.) defend ferociously their host plant (Acacia collinsii) (La Norma Ecolodge). The plant Acacia collinsii have hollow thorns with a hole as entrance for ants, wich protect it against defoliation. (La Norma Ecolodge). Apect of Tropical Dry Forest of Guanacaste in its deciduous phase as preparation to dry season. (La Norma Ecolodge, Guanacaste). Woody lianas are plentiful in the dry forest, as these in a "Guácimo" tree (Guazuma ulmifolia). (La Norma Ecolodge, Guanacaste). The mystery and greatness of evolution are present in the Tropical Dry Forest. (La Norma Ecolodge, Guanacaste).
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Tropical Dry Forest Pictures of Costa Rica
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Tropical Dry Forest imposes Evolutive Adaptations to Survive

 The Tropical Dry Forest Biome is very important because is the most threatened terrestrial environment by the human intervention. In this kind of environment only survive the species adapted to the restriction in the availability of nutrients and water. All the tropical dry forest plants and the animals that live among them had developed evolutive adaptations in order to live in conditions of very less food and water than at the rainforest. Those conditions had enforced plants to lose their leaves during drought, as a way to avoid the lose of essential water; and animals to require large territories to ensure the enough supply of food in an adverse and no plenty region.

Burrowing Toad (drawing by Gustav Mützel) As an extraordinary example of evolutive adaption to survive during dry season, the Burrowing Toad (Rhinophrynus dorsalis) gets backwardly into the soil, using its legs, and remains underground protected from exterior dehydration and heat, but with the first rainfalls after the drought (May - June), comes out to emit sonorous calls and reproduction.

Tropical Dry Forest. Guanacaste, Costa Rica
(Landsat Thematic Mapper)
Source: Landsat.org, Global Observatory for Ecosystem Services, Michigan State University.
Bosque Tropical Seco de Costa Rica (Landsat Thematic Mapper)
Costa Rica Tropical Dry Forest is well identifiable by its deciduous nature, which is as evolutive adaption of plants and trees for avoid the lose of water that happens naturally by the transpiration through the special pores of the leaves (or stomata): while let them drop, the valuable water contained into their stems and tissues does not have way to scape out, and it remains into the plant body during the months with no rainfall. This fact is something that can be seen from space, as it can be distinguished between the lack of green foliage in the area of Guanacaste and along the Nicoya Gulf, as depicted in the satellite image at left.
The springs are less frequent, and most of them diminish their flow, or even becomes dry as drought arrives, but their provision of pristine water injects life to the dry forest. Its geographic location and low altitude optimize the sunlight conditions for the plant photosynthesis, with which dry forests also contribute to the fixation of the carbon present in the atmosphere, but this is in less grade than the rainy forests due to the less density of the forest and the fact of being deciduous (As with the photosynthesis valuable water will be lost by transpiration, this is totally restricted with the leaves fall).

Tropical Dry Forest Animals

Despite the restrictions in water and resources, Nine Banded Armadillo the tropical dry forest is the 2nd in biodiversity below the rain forest, and is inhabitated by a great amount of animals, from which some of the most representatives that can be seen are the Black Iguana (Ctenosaura similis), the previously mentioned Burrowing Toad (Rhinophrynus dorsalis), the White-tailed Deer (Odocoileus virginianus) the Nine-banded Armadillo (Dasypus novemcinctus), the Variegated Squirrel (Sciurus variegatoides), the Paca (Agouti paca), the Agouti (Dasyprocta punctata), the Howler Monkey (Alouatta palliata), the Kinkajou (Potos flavus) and the White-nosed Coati (Nasua narica).

White-throated Magpie-Jay Turquoise-browed Motmot The nice White-throated Magpie-Jay (Calocitta formosa) and the Turquoise-browed Motmot (Eumomota superciliosa) are two very gorgeous and conspicuous birds whose habitat is exclusively the dry forest. But this kind of forest also offers another very good opportunities for bird watching: parrots like the Orange-chinned Parakeet (Brotogeris jugularis), the Red-lored Parrot (Amazona autumnalis), the White-fronted Parrot (Amazona albifrons) or the Orange-fronted Parakeet (Aratinga canicularis), humming birds like the Cinnamon Hummingbird (Amazilia rutila), tanager as the Blue-gray Tanager (Traupis episcopus), the Violaceous Trogon (Trogon violaceus), the Blue-crowned Motmot (Momotus momota) or the Squirrel Cukoo (Piaya cayana) and the no less amazing Long-tailed Manakin (Chiroxiphia linearis). There are also another kind of brids like the Ringed Kingfisher (Megaceryle torquata), or the Collared Aracari (Pteroglossus torquatus), the Pale-billed Woodpecker (Campephilus guatemalensis), doves like the White-winged Dove (Zenaida asiatica). And the most common like the Clay-colored Robin (Turdus grayi), which is the national bird of Costa Rica ("Yigüirro"), the boisterous Great Kiskadee (Pitangus sulphuratus) or the nocturnal Common Pauraque (Nyctidromus albicollis).

Tropical Dry Forest Plants

This forest features two different layer of trees, one of shrubs and the ground plants layer; each of them have different populations of animals and plants adapted to living at its respective place.
The canopy layer tree in the tropical dry forest is of a height of 20 to 30 m, with long and wide trunk, but of lesser dimensions that the trunk of the rainy forests, with extended and plain canopy without contact with the other trees, and are deciduous in the dry season. The predominant leaf in these trees is compound and narrow, and the best example of this is the Guanacaste tree (Enterolobium cyclocarpum). Also very striking because of its beauty and coloration of plenty flowers are the "Cortés Amarillo" Tree (Tabebuia ochracea) with yellow trumpet flowers and the "Malinche" Tree (Delonix regia) featuring a red or reddish-orange inflorescence. Among others species of tropical dry forest trees are the "Pochote" (Bombacopsis quinata), "Guapinol" (Hymenaea courbaril), "Indio Desnudo" or "Jiñocuave" (Bursera simaruba) and "Caoba" (Swietenia macrophylla). Besides there are the "Jocote" (Spondias purpurea) and "Jobo" (Spondias mombin) trees, both with edible fruits and very popular in the former.

The understorey layer is constituted by trees (mainly from Rubiaceae family) from 10 to 20 m of height, with narrow trunks and light canopies. The shrub layer have plants from 2 to 5 m of height, with multiple stems and thorns. There is few presence of epiphytes, and the most predominant are the bromeliads and cacti. Woody lianas are common. The tree canopy set, which are no touching among them does not restricts the incidence of solar light to the ground, so the lower plants and shrubs can propagate in a more easy way than if at other forest kind.

The seed dispersal role of some tropical dry forest animals is a strong link between the ecosystem members, in such a way that the seeds of each fruit eaten and carried by the monkeys or birds have the chance to be "delivered" far away from its producer plant, because of dropping or liberating them when the digestion process completes, incrementing the survival possibilities of that plant and its dispersion potential as well. When this relation is broken, the surviving of the vegetal specie is in serious risk. That is the case of the Guanacaste tree (Enterolobium cyclocarpum), that has been left without its natural seed dispersal agent, and is in extinction danger.

Significance and Value of the Dry Forest

We must save the tropical dry forest because of its already cited vulnerability, the threats that faces and its specialized biodiversity. From the Biology point of view, it can be stated five main reasons to strive in its restoration and conservancy (5):

  • The water scarceness in the dry season.
  • The big mammals inhabiting it require big areas of territory to keep healthy populations.
  • Migration routes towards moist zones in the dry season must be protected.
  • A big and continuous area of tropical dry forest is needed to minimize the impact of agricultural from the limits to its inside.
  • A big territory is required to ensure the existence of the different habitats that constitute it and make it beneficial.


Notes & References:
1
Janzen, D. (1988) Tropical dry forests. The most endangered major tropical ecosystem. In: Wilson, E.O. (ed). Biodiversity. National Academy of Sciences/Smithsonian Institution, Washington DC.
2
Holdridge, L. R.; Genkre, W. C.; Hatheway, W. H.; Liang, T.; & Tosi; J. A., Jr. (1971). Forest environments in tropical life zones: A pilot study. Pergamon Press.
3
From annual averages of weather data at several sites along more than 10 years previous to 2010. Instituto Meteorológico Nacional (Costa Rica National Weather Institute).
4
J. Calvo-Alvarado, B. McLennan, A. Sánchez-Azofeifa, & T. Garvin (2009). Deforestation and forest restoration in Guanacaste, Costa Rica: Putting conservation policies in context. Forest Ecology and Management, 258 (6), 931-940. (05 September 2009).
5
Janzen, D.H. 1988b. Guanacaste National Park: Tropical ecological and Biocultural restoration. In Rehabilitating damaged ecosystems, Vol. II, J. J. Cairns, ed., CRC Press, Boca Raton, Florida, pp. 143-192.
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