A lake in Yauco

A lake in Yauco

The tropical climate has been a determining factor in the kinds of soil and vegetation that have developed in the geographic zone of the Caribbean. This article uses the example of Puerto Rico to describe the common types of soil and vegetation in the Caribbean region.

Soil is a mixture of small particles that originate from the breakdown of rocks and minerals and the decomposition of plants and animals, all of which accumulates on the surface of the earth. Soil is extremely important because it is the medium in which most plants grow, it serves to anchor them and provides nutrients and water for absorption. The soil also stores water, supplying rivers, lakes or reservoirs and aquifers. This makes soil a vitally important resource for the majority of terrestrial animals, including humans.

Soils are formed by the combination of five factors: 1) the type of rock from which it comes, 2) the relief or slope of the land, 3) geological time, 4) organisms (in other words, the types of plants and animals), and 5) the climate. Soils have been categorized and named based on their main characteristics. In Puerto Rico, as in other islands of the Caribbean, the most common soils are:

1) Inceptisols – These are the most common soils in Puerto Rico. They are mainly located in the east-central zone of the island. These are relatively young soils, associated with steep slopes and with good drainage. In the past, inceptisols were used for planting tobacco.

2) Histosols – These soils contain a high concentration of organic material and are located in zones that experience flooding. In Puerto Rico, these soils are associated with wetlands such as the Tiburones channel in Arecibo and in mangrove stands around the island.

3) Mollisols – These soils are black in color and have high fertility and have high amounts of organic material, but unlike histosols, most of the particles of these soils are derived from rocks and minerals. They are found around the limestone “mogote” hills and in the dry plains of southern Puerto Rico.

4) Ultisols – These are clay soils with high acidity and low fertility, associated with the west-central zone of Puerto Rico. These soils have been used for planting coffee.

5) Alfisols – These are clay soils similar to ultisols but more fertile and non-acidic. They are found in the karst region of the northwest.

6) Oxisols – These are the archetype of tropical soils. They are geologically old, red in color, with low fertility and good drainage. They are found on the northwestern plains, in some parts of the interior and in the western part of the island.

Sump

Sump

Vegetation varies based on precipitation and temperature, among other factors. Additionally, vegetation in the Caribbean is subject to natural events, such as hurricanes, and the use of the soil by humans, which modify its development and organization. The types of vegetation, like soils, have been classified based on certain characteristics. The predominant types of vegetation in Puerto Rico are:

1) Dry subtropical forest – This kind of forest is found in southern and southwestern Puerto Rico. The vegetation in dry forests is distinguished by the presence of succulent plants and plants with thorns. On the coasts, the dry forest consists mainly of mangrove swamps. Examples of common plants in the dry forest are the gumbo-limbo tree (Bursera simaruba) and the lignum vitae tree (Guaiacum officinale). The soils associated with this kind of vegetation may be very fertile, such as mollisols, for example. Today, much of the dry forest zone is used for pasture for livestock.

2) Moist subtropical forest – These areas are found in the northern, western, eastern and central zones of Puerto Rico. They are characterized by the presence of tall trees with rounded crowns and the presence of some epiphytes (such as orchids and bromeliads). As in the dry forest zones, mangrove stands are found along coastal areas. Two common trees in the moist forest are the royal palm (Roystonea borinquena) and the trumpet tree (Tabebuia heterophylla). The moist forest zone has been intensely used for agriculture, including growing coffee, tobacco, sugar cane and pasture for livestock. The soils are varied in these kinds of forests and include inceptisols, oxisols and ultisols.

3) Wet subtropical forest – This kind of forest is found in areas of Puerto Rico with high levels of precipitation (approximately 2,000 to 4,000 millimeters of rain per year). These forests are characterized by the presence of epiphytes and trees such as the candlewood or tabonuco (Dacryodes excelsa). Today, most of these forests are secondary and have arisen on abandoned farmland. The soils in this zone are varied and include ultisols and inceptisols.

4) Subtropical rain forest – This forest is located in areas of high elevation and precipitation (more than 3,600 millimeters of rain per year) in the Luquillo mountain range. The vegetation in this zone is similar to the wet forest but contains a greater abundance of epiphytes and a large number of palms. The soils in this forest zone are often saturated with water throughout the year, which leads to runoff.

Due to socio-economic changes, Puerto Rico has gone from being a rural agricultural society to an industrial one. Many farms have been abandoned, allowing the growth of secondary forests. These forests are home to many species of plants and animals, some of which are in danger of extinction. Forests also help conserve the soil, protecting it from erosion and thereby protecting bodies of water from sedimentation. Many of these forests are threatened today by urban sprawl. Understanding forests and the soil is the first step toward protecting them, as they are critically important for the development and sustainability of Puerto Rico.

 

Author: Rafael Méndez Tejada
Published: December 23, 2011.

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