What Are Tropical Dry Forests?

Tropical dry forests approximately account for 42% of the potential tropical global vegetation (Waeber et al. 2015). Although tropical dry forests are less diverse than tropical rain forests, tropical dry forests are still considered to be biodiversity hotspots and are home to many endemic species. However, tropical dry forests are also one of the most threatened and least protected biomes (Waeber et al. 2015).

Distribution of tropical dry forests. Figure by Center for International Forestry Research (CIFOR).

Tropical dry forests typically occur near the equator and can have a range of 10°N to 23°S and are typically situated near windward coasts and leeward sides of mountains or islands (Navarro et al. 2014). Like most tropical climates, tropical dry forests are consistently warm and frost proof with an annual average of 25°C or higher. A major characteristic of tropical dry forests are the extensive dry season that can be anywhere from 5-8 months long (Center for International Forestry Research (CIFOR) 2014). This is due to the Intertropical Convergence Zone, which migrates north and south seasonally, producing alternating patterns of dryness and rainfall (Navarro et al. 2014). Annual rainfall is most intense during the summer months with averages ranging from 600mm to 1600mm (Food and Agriculture Organization of the United Nations n.d.). In contrast, the dry season can receive less than 100mm of precipitation per month (Banda-R et al. 2016). Because of the variability in precipitation patterns, these forests are dominated by drought-deciduous trees; small leaved evergreens and broadleaved sclerophyllous-leaved trees are also found but much less common (Navarro et al. 2014).

Comparing coverage between wet and dry seasons. Left: Photo by Guanacaste Dry Forest Conservation Fund. Right: Photo by Alejandro Muñoz-Urias, Alvaro Edwin Razo Leon

Tropical dry forest canopies average anywhere from 15m to 25m tall, with 3-5 structural levels consisting of upper level canopies, subcanopy trees and shrubs, woody vines, and herbaceous plants (Navarro et al. 2014). During the wet season, the structural levels are well defined. However, canopy cover decreases during the dry seasons and structural levels are less defined.

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Like tropical rain forest, the predominant soil type are oxisols; utisols, alfisols, mesotrophic soils, and limestone substrates are also found but are much rarer (Navarro et al. 2014). Soils are highly weathered, have high iron levels (gives soils a reddish color), low mineral nutrient content, and frequent laterization (Navarro et al. 2014)

Soil types found in tropical dry forests; a.) ultisols b.) alfisols c.) oxisols. Photos by the University of Idaho.

Where Can You Find Tropical Dry Forests?

Citations:

Banda-R, K., A. Delgado-Salinas, K. G. Dexter, R. Linares-Palomino, A. Oliveira-Filho, D. Prado, M. Pullan, C. Quintana, R. Riina, G. M. Rodriguez M., J. Weintritt, P. Acevedo-Rodriguez, J. Adarve, E. Alvarez, A. Aranguren B., J. C. Arteaga, G. Aymard, A. Castano, N. Ceballos-Mago, A. Cogollo, H. Cuadros, F. Delgado, W. Devia, H. Duenas, L. Fajardo, A. Fernandez, M. A. Fernandez, J. Franklin, E. H. Freid, L. A. Galetti, R. Gonto, R. Gonzalez-M., R. Graveson, E. H. Helmer, A. Idarraga, R. Lopez, H. Marcano-Vega, O. G. Martinez, H. M. Maturo, M. McDonald, K. McLaren, O. Melo, F. Mijares, V. Mogni, D. Molina, N. d. P. Moreno, J. M. Nassar, D. M. Neves, L. J. Oakley, M. Oatham, A. R. Olvera-Luna, F. F. Pezzini, O. J. R. Dominguez, M. E. Rios, O. Rivera, N. Rodriguez, A. Rojas, T. Sarkinen, R. Sanchez, M. Smith, C. Vargas, B. Villanueva, and R. T. Pennington. 2016. Plant diversity patterns in neotropical dry forests and their conservation implications. Science 353:1383–1387.

Center for International Forestry Research (CIFOR). 2014. Tropical Dry Forests: Under Threat & Under-Researched. Pages 1–4.

Navarro, G., D. Faber-Langendoen, and E. Helmer. 2014. F003 Tropical Dry Forest & Woodland Formation. https://www1.usgs.gov/csas/nvcs/nvcsGetUnitDetails?elementGlobalId=860270.

Waeber, P. O., L. Wilm, B. Ramamonjisoa, C. Garcia, D. Rakotomalala, Z. H. Rabemananjara, C. A. Kull, J. U. Ganzhorn, and J.-P. Sorg. 2015. Dry forests in Madagascar: neglected and under pressure. International Forestry Review 17:127–148.