About Field Sites
The Guanica Dry Forest Reserve (GUAN) is a terrestrial NEON field site located in a subtropical dry zone along the southern coast of Puerto Rico. The 34.9km2 (8630 acre) site is encompassed within the Guanica State Forest and Biosphere Reserve and managed by the Commonwealth of Puerto Rico’s Department of Natural and Environmental Resources. The forest was designated as a Biosphere Reserve by the United Nations in 1981 and supports numerous global ecological research programs. The area is characterized by low annual rainfall and high evapotranspiration. Plant species along the reserve include cacti, grasses, and shrubs and the forest has of areas with semi-evergreen, deciduous and scrub trees. This location is part of the NEON Atlantic Neotropical Domain (D04), which includes the island of Puerto Rico and the southern tip of Florida. The Domain includes one additional terrestrial field site and two aquatic field sites.  
The Guanica Dry Forest lies within the Subtropical Dry Life Zone, characterized by a warm climate with low annual rainfall averaging 840 mm (33 in.). The average annual temperature is warm at 23°C (73°F). Climate within the forest is influenced by a heat island effect that displaces rain-carrying clouds and creates a warmer, dryer climate produced by the Cordillera Central, a mountain range running east to west across almost the full length of Puerto Rico. Rainfall is distributed in two rainy seasons, one in the spring and the second in the late summer and fall corresponding with the hurricane season. The site can be subject to hurricanes, which are an important feature of the climate of the Atlantic Neotropical Domain.   
The GUAN site is composed of basal gravel to conglomerate overlain by limestone, known as the Juana Diaz Formation. Its estimated thickness is about 850 m. This geology can also be observed at the municipalities of Santa Isabel (Descalabrado River), Ponce (Punta Cuchara Reserve), Penuelas, Guayanilla (Punta Verraco Farm), Sabana Grande, and Guanica.   
The soils of Guanica Forest are derived from limestone formed from marine deposits. Soils are typical to the region: fine-loamy, mixed, carbonatic, typic haplocalcids. These soils are from the Aridisol taxonomic order used to describe dry, desert-like soils with low organic content which are sparsely vegetated by drought- or salt-tolerant plants.   
The Río Loco/Guánica Bay watershed is located in the southwest corner of Puerto Rico, covering portions of Guánica, Yauco, Lajas and Cabo Rojo counties and discharging into the Guánica Bay. It is considered one of the major riparian discharge points in the southwest coast. This watershed is highly manipulated and is used as a drinking water supply by local populations in these counties as well as for irrigation of crops and flood control in the Lajas Valley. 
The Guanica Dry Forest Reserve is home to over 700 plant species and divided into three groups: upland deciduous forest, semi-evergreen forest, and the scrub forest closest to the shore. The vegetation is thick and dense with many multiple-stemmed trees. Forest cover is a mosaic of mature native forest of >100 years old and secondary forests dominated by native and introduced species.  
The Guanica Dry Forest is home to a very diverse range of fauna that includes both marine and terrestrial wildlife. The coast side of the reserve provides habitat to all kinds of coral reefs, including many coral species and the West Indian manatee (Trichechus manatus). Within the forest, there are approximately 136 species of birds, of which eight are classified as threatened or endangered. Within this group of species is the Puerto Rican nightjar (Caprimulgus noctitherus). In addition, there are many species of reptiles including the endangered Puerto Rican Boa (Epicrates inornatus) and amphibians such as the Puerto Rican crested toad (Peltophryne lemur). Insects include grasshoppers; beetles; ants; and mosquitoes such as Aedes aegypti, Aedes taeniorhynchus, and Culex erraticus. NEON provides data on five types of wildlife: small mammals, birds, mosquitoes, ticks, and ground beetles.  
Past Land Management and Use
The town of Guanica was founded in 1508 and was once a major indigenous capital for the Taino people. Past last management for the Guanica Dry Forest dates back to the island’s Spanish settlement with the establishment of land distribution and forest inspection. By that time, the primary uses of forested areas were for pastures, timber, charcoal production and coconut plantations, although the now-known reserve boundaries were to clear during that time. In 1917, the Guanica Dry Forest was designated a state forest by Governor Yager and it became a protected area in 1930. Because of various land acquisitions over the years, by 1919 the reserve became the third-largest forest reserve on the island after the Yunque Rain Forest and the Maricao Forest Reserve. This area has been subjected to a wide variety of activities and uses throughout its history, including tree plantations of Logwood (Haematoxylum campechianium) and West Indian Mahogani (Swietenia mahogani), agriculture (cultivated crops and livestock), and human settlements. According to Murphy and Lugo, there were human settlements within the boundaries of the forest; these settlements disturbed the forest through selective logging for timber, posts production and charcoal, along with some cattle grazing. Later, these settlements were moved to La Luna, a housing area located in the north entrance area of the Reserve. Several reforestation projects have since been conducted in the Reserve.  
Puerto Rican infrastructure and forest structure are periodically disrupted by hurricanes and wildfires, and other DNER-recognized threats include invasive species, pests and diseases, forest fragmentation and climate change. Hurricanes Irma and Maria in 2017 devastated Puerto Rico's infrastructure, both human and natural. While natural ecosystems are recovering from defoliation, it will take longer for forest structure to be rebuilt. Hurricane Hugo in 1989 caused wide destruction of trees, and resulted in altered forest composition and changes in growth rates in affected areas.  
Current Land Management and Use
The Commonwealth of Puerto Rico has delegated management of Guánica Dry Forest to the Department of Natural and Environmental Resources (Departamento de Recursos Naturales y Ambientales, DRNA). The Guánica Dry Forest is divided into two sections separated by the Guánica Bay. The western portion, located in Ensenada, is smaller and less intensively managed than the eastern portion. The eastern part of the site contains the original forest reserve, which was designated as a protected reserve in 1930. The Forest was appointed a state forest in 1917 by Governor Arthur Yager and has been protected and managed since 1930. This site supports research from local and state environmental laboratories focusing on flora and fauna biodiversity, invasive species, threated species, endangered species, and land use, among others.   
NEON Site Establishment
NEON plot establishment at GUAN began in December 2015 and was completed in 2016. The site transitioned to operations in July 2016. The terrestrial sampling and observations began in December 2015. Construction of the site’s 23 m (72 ft.), 5-level instrumental tower was completed in 2015, and the tower came online and began streaming data in March 2017.
 Monsegur-Rivera, O.A. (2009). Vascular Flora of the Guanica Dry Forest (Master’s thesis). Available from University of Puerto Rico Mayaguez Campus Library
 United States Department of Agriculture. (May, 2014). Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region, P-07. https://www.srs.fs.usda.gov/pubs/gtr/gtr_srs193.pdf
Terrestrial Observation System (TOS) Site Characterization Report: Domain 04. NEON.DOC.003888vB
 Bawiec, W.J., ed. (1999), Geology, geochemistry, geophysics, mineral occurrences and mineral resource assessment for the Commonwealth of Puerto Rico: U.S. Geological Survey Open-File Report 98-038, 66-77, available online only at https://pubs.usgs.gov/pp/0953/report.pdf.
 U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia. https://mrdata.usgs.gov/mrds/
 Terrestrial Instrument System (TIS, FIU) Site Characterization Supporting Data: Domain 04. NEON.DOC.011032vE
 PRISM Climate Group, Oregon State University, http://prism.oregonstate.edu, created 4 Feb 2004.
 Genet, K., Genet, J. & Burton, T., & Murphy, P. (2001). The lizard community of a subtropical dry forest: Guanica Forest, Puerto Rico. Tropical Ecology. 42.
 Murphy, P & Lugo, A. (2003). Ecology of Tropical Dry Forest. Annual Review of Ecology and Systematics. 17. 67-88.
 USFWS Caribbean Ecological Services Field Office. (2020). List of threatened and endangered species.
 J Carlos Trejo-Torres "A New Shrub Species from a Dry Forest of Puerto Rico, Reynosia vivesiana (Rhamnaceae)," Novon: A Journal for Botanical Nomenclature 18(3), 390-394, (2 September 2008). https://doi.org/10.3417/2005169
 Natural Resources and Conservation Service. (2009). United States Department of Agriculture. Proyecto Cuenca Hidrológica Guánica- Río Loco. Available at https://www.nrcs.usda.gov/wps/portal/nrcs/detail/pr/programs/landscape/…
 Department of Natural and Environmental Resources. (2010). Puerto Rico statewide assessment and strategies for forest resources. Government of Puerto Rico. https://estadisticas.pr/files/BibliotecaVirtual/estadisticas/biblioteca…
 Forest Service International Institute of Tropical Forestry. (2019). A comprehensive inventory of protected areas and other land conservation mechanisms in Puerto Rico. United States Department of Agriculture. https://data.fs.usda.gov/research/pubs/iitf/iitf_gtr_50_eng_lowres.pdf
Remote sensing surveys of this field site collect lidar, spectrometer and high-resolution RGB camera data.
This site has a flux/meteorological tower that is 23 m (75 ft) tall with five measurement levels. The tower top extends above the vegetation canopy to allow sensors mounted at the top and along the tower to capture the full profile of atmospheric conditions from the top of the vegetation canopy to the ground. The tower collects physical and chemical properties of atmosphere-related processes, such as humidity, wind, and net ecosystem gas exchange. Precipitation data are collected by a tipping bucket at the top of the tower, a Double Fence Intercomparison Reference (DFIR) near the tower, and a series of throughfalls located in the soil array.
Soil Sensor Measurements
This site has five soil plots placed in an array within the airshed of the flux tower. Photosynthetically Active Radiation (PAR) at soil surface, soil heat flux, solar radiation, and throughfall are measured at the soil surface in each soil plot. Soil moisture, soil temperature, and CO2 concentration are measured at multiple depths in each soil plot.
At terrestrial sites, field ecologists observe birds and plants, and sample ground beetles, mosquitoes, small mammals, soil microbes, and ticks. Lab analyses are carried out to provide further data on DNA sequences, pathogens, soils, sediments, and biogeochemistry. Learn more about terrestrial observations or explore this site's data products.
State Forest, Dept. of Natural and Environmental Resources, Commonwealth of Puerto Rico
Site Access Allowed
Site Access Details
It is highly recommended that prospective researchers make contact well in advance of any planned work (> 6 months) as there are multiple steps and a high level of coordination that must take place to gain permission and access to this area. All requests will be evaluated on a case-by-case basis by the site hosts.
NEON Field Operations Office
NEON Field Operations Phone
Mean Annual Temperature
Mean Annual Precipitation
Dominant Wind Direction
Dominant NLCD Classes
Average number of green days
Number of Tower Levels
USGS Geology Unit
USGS Geology Name
Juana Diaz Formation
USGS Lithologic Constituents
Basal gravel to conglomerate overlain by limestone.
USGS Geology Age
Middle Miocene to Lower Oligocene
Megapit Soil Family
Coarse, loamy, carbonatic, isohyperthermic. Typic Haplocalcids.
Other Domain 3 Field Sites
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