Guanica Forest is a core terrestrial field site, located in the Guánica Dry Forest reserve and is part of the NEON Altantic Neotropical domain 04. The Guánica Dry Forest which includes the largest tract of dry tropical coastal forest in the world. The area was once underwater, and the forest grows in limestone (karstic soil) formed from ancient coral reefs. It is located on the southwestern shore of the island, where a heat island effect displaces rain-carrying clouds and creates a warmer, dryer climate. The town of Guánica, with a population of just over 9,000, is situated on the outskirts of the reserve. The GUAN field site is located on land managed by the Commonwealth of Puerto Rico Department of Natural and Environmental Resources. NEON researchers work closely with the department to minimize their impact on endangered species in the area. The data collection systems at GUAN include airborne remote sensing surveys, automated instrument measurements and observational field sampling. The meteorological/flux tower is 66' with five measurement levels. There are also multiple plots for soil sensors and sampling and organismal sampling including birds, ticks and mosquitoes. At both D04 terrestrial field sites, scientists collected small mammal data from 2016-2017. Small mammal sampling protocols are currently suspended due to safety issues.