Unearthing Nature's Canvas-Southwest Puerto Rico
A soil expedition in Southwest Puerto Rico, featuring Oxisols, Ultisols, Mollisols, and Aridisols
SSSA Bouyoucos Summer Conference - June 2024
Tour #5
Punta Guaniquilla Nature Reserve
Here, you'll find Mollisols and Aridisols, and a landscape of boulders in the middle of a lagoon, which is truly out-of-this-worldly. These rock formations are part of the southern karst belt and date back to geological processes more than 11,000,000 years old, when Lajas' Sierra Bermeja was one of the islands in the Puerto Rican archipelago.
Guanajibo, Joyuda
Here we'll make a short stop to observe the Guanajibo soil series with the redox patterns and plinthite.
Suelo Nipe
We'll stop near PR-100 to observe the Nipe soil series. The Nipe soil series is formed on weathering serpentinite outcrops near Mayagüez. Serpentinite in this area has been classified as part of a serpentinite mélange, containing pieces of Early Jurassic to Cretaceous chert, amphibolite, metabasalt, schist, gneiss, and greenstone. This soil series falls under MLRA 270—Humid Mountains and Valleys.
Punta Guaniquilla Nature Reserve
Photo by: Zoelie Rivera
The reserve extends from sea level to 46 m in elevation at Cerro Guaniquilla. There are two cave systems in limestone of Cretaceous age, one reputed to have contained petroglyphs in the past. The other, erroneously associated by the public with the death of the famous Cabo Rojo pirate, Roberto Cofresí (1791–1825), has dozens of tunnels.
The land contains upland and wetland habitats with seven major vegetation types:
- Pasture—some areas heavily impacted by grazing
- Shrubland—areas in transition to woodland
- Woodland—canopy from 6 to 9 m tall and dominated by a few tree species
- Evergreen forest—canopy to 12 m with a mixture of several tree species
- Marsh—flooded seasonally for extended periods
- Beach—sand, rocky areas, and few tree species including red mangrove
- Beach thickets—to 5 m tall with several tree species including white and black mangroves
Source: Weaver and Schwagerl, 2009.
Photo by: Nohely Reyes
Soils of Punta Guaniquilla Nature Reserve
The San German series consists of shallow, well drained, very slowly permeable soils on ridge tops, summits and side slopes in uplands of limestone hills and mountains of the Semiarid Mountains and Valleys MLRA. They formed in material that weathered from limestone bedrock of the Cretaceous Period. Near the type location, the mean annual temperature is about 79 degrees F., and the mean annual precipitation is about 35 inches. Slopes range from 5 to 60 percent.
TAXONOMIC CLASS: Clayey-skeletal, mixed, superactive, isohyperthermic Lithic Haplustoll
The San German series extent
The Duey series consists of shallow, well drained, very slowly permeable soils on ridge tops, summits and side slopes of the limestone hills of the Semiarid Mountains and Valleys MLRA. They formed in material that weathered from limestone bedrock of the Cretaceous period. Near the type location, the mean annual temperature is about 77 degrees F., and the mean annual precipitation is about 45 inches. Slopes range from 5 to 60 percent.
TAXONOMIC CLASS: Clayey-skeletal, mixed, superactive, isohyperthermic, shallow Typic Haplustolls
The Duey series extent
The Cerro Mariquita series consists of shallow, well drained, moderately permeable soils on side slopes and summits of hills and mountains of the Semiarid Mountains and Valleys MLRA. They formed in residuum and colluvium material weathered from basalt, chert and rhyolite. Near the type location, the mean annual temperature is about 80 degrees F., and the mean annual precipitation is about 29 inches. Slopes range from 12 to 60 percent.
TAXONOMIC CLASS: Clayey, mixed, active, isohyperthermic, shallow Typic Haplargids
The Descalabrado series consists of shallow, well drained, moderately permeable soils on side slopes and summits of hills and mountains of the Semiarid Mountains and Valleys MLRA. They formed in residuum and colluvium that weathered from basic volcanic rock. Near the type location, the mean annual temperature is about 77 degrees F., and the mean annual precipitation is about 35 inches. Slopes range from 2 to 60 percent.
TAXONOMIC CLASS: Clayey, mixed, superactive, isohyperthermic, shallow Typic Haplustolls
MLRA: 271 - Semi Arid Mountains & Valleys
GEOLOGY
The part of the area in Puerto Rico consists of steep mountainsides composed mainly of Cretaceous rocks. The lower mountains consist of Tertiary limestone. Ultrabasic rocks (serpentinite) occur in Sierra Bermeja, in southwestern Puerto Rico. Together with the chert fragments in the same area, they constitute the oldest rocks on the island. They formed in the Late Jurassic Period, about 150 million years ago. Most of the part of the MLRA in Puerto Rico has a mixture of limestone and volcanic rocks in the higher, steeper areas
CLIMATE
Much of the rainfall is lost through evapotranspiration, and the year-round air temperatures are high. As a result, the climate is semiarid. Most of the rainfall occurs in the afternoons as frequent trade-wind showers from May to October, but tropical storms and hurricanes can produce high amounts of rain and result in widespread flooding. This part of the MLRA is typically drier from December through March, rainy during April and May, semidry in June and July, and wet from August through November.
LAND USE
About 43 % of the MLRA is pasture, consisting mainly of adapted native grasses. About 30 percent is natural forest, and 8 percent supports improved species of hardwoods such as mahogany, teak, and eucalyptus.
Urban expansion is a land use concern.
The major soil resource concerns are water erosion (sheet and rill and ephemeral gully or concentrated flow), maintenance of the content of soil organic matter and tilth, and water infiltration.
Guanajibo and Nipe series
Guanajibo series
The Guanajibo series consists of very deep, well drained, moderately permeable soils on coastal terraces and alluvial fans on humid coastal plains. They formed in fine textured sediments of mixed origin. Near the type location, the mean annual temperature is about 77 degrees F., and the mean annual precipitation is about 68 inches. Slopes range from 2 to 12 percent.
TAXONOMIC CLASS: Very-fine, mixed, isohyperthermic Plinthic Kandiudults
Nipe series
The Nipe series consists of very deep, well drained, moderately permeable soils on stable ridge tops of hills and mountains in the Humid Mountains and Valleys MLRA. They formed in iron-rich residuum that weathered from serpentinite bedrock. Near the type location, the mean annual temperature is about 75 degrees F., and the mean annual precipitation is about 57 inches. Slopes range from 2 to 20 percent.
TAXONOMIC CLASS: Very-fine, ferruginous, isohyperthermic Typic Acrudox
Serpentinite in Puerto Rico is one of the oldest rocks at the Caribbean-North American plate boundary zone.
Serpentinite
MLRA: 270—Humid Mountains and Valleys
- It makes up about 53 % of the island and consists of about 2,135 square miles.
- Boundary to the south with the Semiarid Mountains and Valleys (MLRA 271) that is marked by an ecotone transitioning from the udic to the ustic soil moisture regime.
- Most of this MLRA consists of volcanic rocks that formed below sea level during the Cretaceous Period (135 to 70 million years ago).
- The dominant soils in this MLRA are Inceptisols, Ultisols, or Oxisols. The dominant suborders are Udepts, Humults, Udox, and Perox.
- Additional information in Agriculture Handbook 296
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