St. Maarten is one of the islands forming the inner arc of the Lesser Antilles. It is older than Saba and St. Eustatius. The oldest rock strata date from ± 50 million years ago. The island experienced periods of uplift and descent. In the Pleistocene period it formed one island together with Anguilla and St. Barths.
St. Maarten is irregular in form because of the many bays and lagoons. Steep rocky coasts alternate with sandy beaches. The major part of the island is hilly. Three ridges can be distinguished in the north-south direction. Only the Low Lands in the west are flat. In the past St. Maarten was a plantation island, with sugarcane cultivation reaching high up into the hills. Now tourism is the main economical activity. The island has two parts: The French and the Dutch part. About 38.000 people live on St. Maarten on the Dutch side, especially in the valleys, but also more and more in the hills. Because of the high population density and tourism development a lot of nature has already been lost, and several habitats are under pressure. According to the system of Köppen the climate of Maarten falls between a savanna and monsoon climate. The island is situated in the Atlantic hurricane zone. In September 1995 St. Maarten was hit by a severe hurricane.
At least 522 wild plants are known from St. Maarten, divided in 506 seed plants and 16 ferns. Among the plants there are two island-endemic species: Calyptranthes boldinghgii en Galactia nummelaria. Both species are very rare or have possibly disappeared already. The geographical distribution of five plants is limited to just a few islands and 3.3% of the species is endemic to the Lesser Antilles and the Virgin Islands. With respect to the moss flora, only two true mosses are known, and no liverworts.
The major part of the Dutch side of St. Maarten is covered with secondary vegetation derived from either seasonal formations or dry evergreen formations. Only on the top of the hills some more or less original semi-evergreen seasonal forest is found. This type of forest has regionally become extremely rare too. Locally it includes several species that are lacking elsewhere in the island. Because of its small area this forest formation is very vulnerable. On the higher hills of the two ridges in the middle part of the island, and on the hills of the eastern ridge, a dense secondary woodland vegetation is growing, preventing erosion and with a high scenic value. Along the coast and inland waterways remains of mangrove forests and other types of coastal vegetation survive, which are of high ecological value, and also have scenic value.
The fauna of St. Maarten is poor in species, not only because of St. Maarten’s small size, but also because of habitat destruction, hunting, imported predators and hurricanes. One bird species, the Red-tailed Hawk, Buteo jamaicensis, and two kinds of reptiles, the Antillean Iguana Iguana delicatissima and the original population of the Green Iguana, Iguana iguana, have already been exterminated. Among the vertebrates, birds form the largest group. Especially the number of migrating birds and visitors is big. In total there are 39 resident and nesting birds on St. Maarten and 68 species of migrating birds and visitors have been observed. These include 19 sea birds, of which 10 species breed in or in the vicinity of the island. St. Maarten is classified as an important breeding area for seabirds. Several small rocky islands just off shore accommodate breeding colonies of seabirds. 2 Amphibians and reptiles are the next largest group of vertebrates. They are represented by 15 species. Bats are probably the only native mammals. There are six species on St. Maarten.
The subspecies of the tree lizard Anolis wattsi pogus can be regarded as an island-endemic species. The animal is extinct in other islands. Several vertebrates are endemic for the Lesser Antilles and the Virgin Islands, either at the species level or the subspecies level: one bat, one amphibian and six reptiles. The ground lizard Ameiva pleei, the tree lizard Anolis gingivinus, the gecko Sphaerodactylus sputator, the Grass-snake Alsophis rijersmai and the subspecies of the gecko Sphaerodactylus macrolepis parvus are limited to only a few islands. The White crowned Pigeon Columba leucocephala and the Red-Necked Pigeon Columba squamosa, both regionally and locally rare because of hunting, are still found in the island and could increase because of the diminished pressure of hunting. Among the breeding seabirds three, Audubon’s Shearwater Puffinus lherminieri lherminieri, the Brown Pelican Pelecanus occidentalis occcidentalis, and the Roseate Tern Sterna dougallii dougallii, are endangered and three, the Red-billed Tropicbird Phaeton aethereus mesonauta, the Sooty Tern Sterna fuscata fuscata, and the Least Tern Sterna albifrons antillarum, are possibly endangered. Of the invertebrates not much more is known than 170 names.
The main threats to the biodiversity of St. Maarten are habitat destruction and degradation caused by the growth of inhabited areas, tourism development and pollution. Since the fifties several people argued for the need to preserve valuable nature areas, not only for ecological motives, but also for the benefit of tourism. Stinapa-St. Maarten, the later St. Maarten National Heritage Foundation, and Stinapa Netherlands Antilles, have struggled continuously to establish a hilltop protected area and a nature/culture reserve Belvédère/Bishophill. Their aim should be supported. At present the necesary island legislation is being worked on. For effective nature management in St. Maarten complete floristic surveys are necessary, and further studies of the status of the island populations of regionally and locally scarce and/or endangered species. For now, a few conclusions can be drawn regarding the conservation of biodiversity on St. Maarten. For this conservation it is necessary to safeguard the largest possible contiguous areas of nature. To this aim the following areas are recommended for conservation and management: the ‘Hillsides’, Naked Boy Hill and surroundings, and the hills and coastal area between Guana Bay en Back Bay. For the benefit of the bats the top of Billy Folly is recommended, and for the avifauna the various ponds, coastal habitats and the little islands Pelican key, Molly Beday and Hen and Chickens.