Costa Rican seasonal moist forests

• Category: Forest Biomes.
• Geographic Location: Central America.
• Summary: This unique tropical forest type is characterized by intense seasonal changes, but much has been lost to clearing for agricultural crops and cattle farms, leaving just 10 percent of the land as intact forest.

Costa Rican seasonal moist forests exhibit dramatic changes between wet and dry seasons, including loss of canopy leaves. The landscape differs so completely between seasons that casual observers may not believe it is the same forest. This ecosystem hosts many rare species and serves as a migration site for others. Unfortunately, the loss of forest to farmlands threatens these diverse ecosystems.

Seasonal moist forests occur in two areas of northwestern Costa Rica over a range of elevations. The first is a strip of land bordered on the west by the seasonal dry forests of Guanacaste and on the east by the Tilarán Mountain peaks. Because this mountain range marks the Continental Divide, rain from these forests drains into the Pacific Ocean. A smaller area of seasonal moist forests lies on the Nicoya Peninsula, which curves southward and also drains into the Pacific Ocean.

Day length and temperature remain relatively constant throughout the year, but tropical Costa Rica experiences distinct wet and dry seasons. Seasonal moist forests receive about 59 inches (1,500 millimeters) of rain during the wet season (May to November) and less than 6 inches (150 millimeters) of rain from December to April. The especially severe dry season in this region results from the constant activity of the trade winds during winter months. The winds blow across the country from east to west, but the high Tilarán Mountains trap the moisture they bring from the Caribbean. Thus, dry winds sweep the northwestern Pacific slope, eliminating moisture from the land.

In the neotropics, seasonal changes in precipitation affect reproductive schedules, migration patterns, soil nutrient cycles, and other ecosystem factors. In seasonal moist forests, the annual canopy loss and accumulation of leaves on the forest floor give seasonality even greater importance. Many organisms have specialized mechanisms to cope with the changes in light penetration and nutrient cycling, giving seasonal moist forests a unique composition of species.

As in most of the neotropics, the species of this region are poorly documented. Species composition changes greatly over short distances in these forests due to significant alterations in elevation and overall rugged topography. Therefore, protecting seasonal moist forests throughout the region is critically necessary to conserve biodiversity.

Vegetation and Wildlife

Seasonal moist forest trees and shrubs consist of a mix of deciduous broadleaf and conifer species such as clusia, cedar, pochote, and the national tree of Costa Rica: the guanacaste (Enterolobium cyclocarpum). Orchids, bromeliads, and lianas create diverse habitats on tree trunks and branches. These epiphytes occur with less abundance in the region than in neighboring montane forests.

The unseen and unsung heroes of the seasonal moist forest are fungi. Though visible above ground only during reproductive phases, they occur in soil, plant roots, and on the surfaces of plants and animals. The forest requires fungi for the breakdown of leaf litter and the provision of nutrients to plants.

The forest floor here abounds with diversity and activity. Agoutis, coatamundis, jagarundis, and tyras roam in search of food. There also are innumerable species of invertebrates such as beetles, centipedes, scorpions, and spiders, many of which remain unidentified. Though often invisible in their underground chambers, ants are estimated to have a higher total biomass than all other animal species combined in these forests; they play essential roles in nutrient cycling and in carving out and tending to various habitat niches.

The understory and canopy host characteristic animals such as tree frogs, butterflies, vine snakes, bats, howler monkeys, and spider monkeys. Hundreds of birds, including white-fronted parrots, laughing falcons, and oropendulas make their home in the forest here. Seasonal moist forests also serve as a migration destination for notable bird species like resplendent quetzals and three-wattled bellbirds, which travel from the east to eat from later-fruiting trees here.

Threats and Conservation

Global warming is the source of future trouble for this biome. Disruption to wind patterns, long-term temperature rise, and higher frequency of violent weather events may combine to drive soil erosion, altered seasonality, failed reproductive cycles, and other habitat-endangering trends. Plants and animals that have evolved specifically to take advantage of the predictable dynamics of the seasonal moist forest will be jeopardized as these climate changes work to unravel the timing, temperature, and humidity regimes that they have grown to depend upon.

Seasonal moist forests are among the Costa Rican ecosystems most affected by habitat loss and degradation. In the past century, lowland seasonal moist forests have been cleared for beef cattle, while higher-elevation forests have been replaced by coffee, beans, corn, and dairy cows. Only 10 percent of the seasonal moist forest region remains intact forest.

Although conservation efforts are relatively high in Costa Rica, only 3 percent of land in seasonal moist forest regions are protected, making them the least-represented ecosystem in the national park system. Protected areas include Cabo Blanco on the Nicoya Peninsula, established in 1963 as the country's first nationally protected land; and Parque Nacionál Rincón de la Vieja, which protects a significant tract of eastern seasonal moist forests.

Many birds require continuous habitat to complete migratory paths. Thus, deforestation and fragmentation have dramatically reduced populations. Deforestation has occurred in the country since the 1500s. In 1994, Costa Rica had one of the highest rates of deforestation in Central America. While the country has taken many steps to try to preserve its forests and slow the rate of destruction, the damage already done still threatens species such as migratory birds. The Bellbird Biological Corridor Project works to connect forest fragments and ensure the future of these species.

Recently, international ecotourism has become a reason for promoting preservation and reestablishment of these forests. The revenue brought in by bird-watchers, hikers, and other nature-lovers has fueled several conservation-related subsidy programs, such as the payment of farmers to allow their fallow land to reforest. Ideally, increased interest in this region will allow seasonal moist forests to persist for future generations to enjoy.

Bibliography

Janzen, Daniel. Costa Rican Natural History. Chicago: University of Chicago Press, 1983.

Kricher, John C. A Neotropical Companion: An Introduction to the Animals, Plants, and Ecosystems of the New World Tropics. 2nd ed. Princeton, NJ: Princeton University Press, 1997.

Olson, David M., et al. “Terrestrial Ecoregions of the World: A New Map of Life on Earth.” BioScience51, no. 11 (2001).

Rappole, John H. The Ecology of Migrant Birds: A Neotropical Perspective. Washington, DC: Smithsonian Institution Press, 1995.

Rodwin, Dana. “The Endangerment and Conservation of Wildlife in Costa Rica.” Connecticut College, 2020, digitalcommons.conncoll.edu/cgi/viewcontent.cgi?article=1015&context=sip#:~:text=In%20this%20analysis%2C%20I%20discuss,individual%20members%20of%20the%20species. Accessed 19 Nov. 2024.