Costa Rican seasonal moist forests
The Costa Rican seasonal moist forests ecoregion is quite different from the surrounding dry and moist forest habitat types. Deciduous trees that shed leaves during the distinct dry season make up the dominant vegetation in these forests. The ecoregion fauna have a moderate species richness, with the number of vertebrates occurring here amounting to 698 taxa; however, faunal endemism is rather low. The flora are more adapted and capable of surviving in such a seasonally based ecoregion. Animals also are adapted to this fluctuation between wet and dry climate changes, and the subsequent changes in the plantlife.
The natural environment of this ecoregion has been substantially destroyed, chiefly by deforestation by the Costa Rican and Nicaraguan people, to clear land for grazing of livestock and other agricultural uses. Disruption to the Nicaragua portion of the ecoregion has also been aggravated by rebel warfare during the latter part of the twentieth century, sponsored by Cuban and Soviet intervention and arms supplies beginning in 1979.
Location and general depiction
This relatively small ecoregion lies on the Pacific Ocean versant, spanning the borders of northwestern Costa Rica and Nicaragua, between the crests of Costa Rica's central chain of volcanoes on the east and the Pacific Ocean on the west. The rainshadow created by Tilaran Mountain Range gives this ecoregion's climate significant seasonal variability. For about five months, usually November through March, the nearly incessant easterly tradewinds bring moisture-laden air from the Caribbean Sea that is trapped on Central America's Atlantic slope by the tops of the mountains, depriving the Pacific side of the Isthmus precipitation. During the rest of the year, the tradewinds are absent or substituted by reversed movements of air created by low pressures from hurricanes in the Caribbean Sea, and orographic uplift and resultant cooling of air from the Pacific Ocean inundates the area with heavy rainfall. Approximately 225 millimetres (mm) fall monthly during this time of year. Often referred to as the wet season, it comprises around ninety percent of the 1500 mm of annual precipitation.
The deciduous vegetation here distinguishes this ecoregion from wetter ecoregions to the south and east and quickly increases in dominance as one moves west from the cloud forest habitat of the mountain peaks. During the dry season, most canopy trees are leafless; moreover, at lower elevations only the riparian forests are evergreen.
The flora of this seasonal moist forest ecoregion exhibits extremely high beta diversity, which is to say its species composition changes rapidly over short distances as one moves away from the adjacent highland cloud forests, down the mountains into areas increasingly impacted by the rainshadow. The colonizing human population preferred this ecoregion's more arid climate and largely converted it to an agricultural landscape as long as 80 to 110 years ago. Thus, in the absence of protected areas, or even large intact blocks of habitat, taxonomists have poorly researched the area.
Perhaps the most outstanding characteristics of these Pacific versant habitats is their tight ecological linkage to the wetter habitats of the adjacent mountain tops and Atlantic slopes. Many species of invertebrates and birds migrate seasonally between these habitats. Some of the most charismatic cloud forest species such as the Resplendent Quetzal (Pharomacrus mocinno) and Three-wattled Bellbird (Procnias tricarunculata) are equally dependent on the seasonal moist forests as they migrate annually to these moist forests at the completion of their breeding season. These birds apparently migrate into the moist forests to take advantage of delayed fruiting cycles of tree species, predominately of the Lauraceae family, that are endemic to the ecoregion.
There are diverse plant taxa within this ecoregion. One of these is the spiny cedar, or pochote, which is readily distinguished by sharp, conical spines emanating from the bark; its white shaving brush flowers are pollinated nocturnally by various bat taxa. There are numerous special status taxa that are found in the Costa Rican seasonal moist forests ecoregion, denoted variously as Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).
Mammalian fauna found in this ecoregion include: Central American Montane Squirrel (Syntheosciurus brochus NT); Variegated Squirrel (Sciurus variegatoides), Mantled Howler Monkey (Alouatta palliata); White-throated Capuchin Monkey (Cebus capucinus); Central American Spider Monkey (Ateles geoffroyi EN); Central American Agouti (Dasyprocta punctata); White-nosed Coati (Nasua narica); and the Jaguarundi (Puma yagouaroundi).
A number of reptilian species are found in the ecoregion, including; Degenhardt's Scorpion-eating Snake (Stenorrhina degenhardtii); Godman's Montane Pit Viper (Cerrophidion godmani); Oxacan Spiny-tail Iguana (Ctenosaura quinquecariniata EN), who prefers rocky terrain and is found only in the Pacific versant of Costa Rica and Nicaragua; and the Yellow-headed Gecko (Gonatodes albogularis).
A number of amphibians are found in the Costa Rican seasonal moist forests ecoregion. Salamanders present include the Costa Rican Worm Salamander (Oedipina uniformis); Alvarado's Salamander (Bolitoglossa alvaradoi EN); and LaPalma Salamander (Bolitoglossa subpalmata EN). A caecilian found in the ecoregion is the Mexican Caecilian (Dermophis mexicanus VU). There are a number of anuran taxa found in the ecoregion, including the Yellow Toad (Incilius luetkenii).
The Costa Rican seasonally moist forests have been extensively altered by human intervention. Lowland areas have been cleared for cattle, while mountain slopes, regardless of their steepness, have been cleared to grow beans, corn, coffee, as well as to support dairy cattle; most of Costa Rica's population and a significant portion of Nicaragua's lives within this ecoregion. During the past 100 years, virtually the entire ecoregion has been stripped of its native vegetation, with only small forest fragments remaining, totaling less than ten percent of the ecoregion's original forest cover. Additional destruction occurred in Nicaragua in the latter twentieth century, when armed conflict began between Cuban backed Sandanista rebels and the government.
The lack of lower and middle-elevation Pacific Slope forests threatens both the species that reside in these habitats and the altitudinal migrants the breed in the neighbouring highlands. The small protected areas in the ecoregion total less than 30,000 hectares, or approximately three percent of the ecoregion. In addition, this ecoregion is considered one of the least represented by National Parks within all of Mesoamerica.
Ecological threat profile
Since the start of the twenty-first century, there has been some regeneration of lower-elevation hillsides, following the collapse of Costa Rica's cattle industry due to rising labour costs and decreasing yields after soils became exhausted from annual burning, overgrazing, and resulting erosion. However, above 800 metres, the situation remains critical as a growing human population puts ever-increasing demands for living space and agricultural products that thrive in the moderate mid-elevation climate.
Justification of ecoregion delineation
These transitional forests mark a unique and graded ecotone between the moist forests and dry forests of Costa Rica and Nicaragua, and host endemic species as well as maintain unique processes such as elevational migrations of many species. This region is distinct from surrounding areas in both floral and faunal distributions. Delineation for the ecoregion is derived chiefly from Holdridge and Tosi to encompass the "humid tropical forest" life zones of the Pacific versant of northern Costa Rica and southern Nicaragua. On the Nicoya Peninsula and along the slopes of the Cordillera Central, small aggregates of "very humid tropical forest" life zones were lumped for broader scale coverage. As well, this ecoregion was separated from the Caribbean slope portions of these same life zones on the basis of species distributions. Isla Ometelepe was on Lake Nicaragua and the volcanic mountains around the northern portion of the lake were also included due to species similarities. Portions of similar habitat south of the Central Valley of Costa Rica were not included on the basis of distinct floral and faunal distributions.
- E. Coen. 1983. Climate. In D. H. Janzen, editor, Costa Rican Natural History. Chicago: University of Chicago Press. ISBN: 0226393321
- W. A. Haber. 2000. Personal communication.
- L. R. Holdridge. 1962. Mapa ecólogico de Nicaragua. Agencia para el Desarrollo Internacional de Gobierno de los Estados Unidos de America, Managua, Nicarauga.
- L. R. Holdridge. 1967. Life zone ecology. Tropical Science Center, San Jose, Costa Rica.
- Andres Oppenheimer. 1993. Castro'S Final Hour. Simon and Schuster. 474 pages
- S. Palminteri. 2000. Personal observation.
- G.V.N. Powell. 2000. Personal communication.
- Powell, G. V. N., and R. D. Bjork. 1994. Implications of altitudinal migration for conservation strategies to protect tropical biodiversity: a case study of the Resplendent Quetzal Pharomacrus mocinno at Monteverde, Costa Rica. Bird Conservation International (4).
- F.G. Stiles and A. F. Skutch. 1989. A guide to the birds of Costa Rica. New York: Cornell University Press. ISBN: 0713635126
- J.A. Tosi Jr. 1969. Republica de Costa Rica: mapa ecológico. Map 1:750,000. Tropical Science Center, San Jose, Costa Rica.
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