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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. [2] [6] [7]

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. [4] [5] [11]

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. [3] [4] [6]

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. [12]

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. [3] [6]

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. [3] [10]

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. [1] [9]

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. [13] [14]

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. [1] [8] [9]

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.