Yap tropical dry forests

The Fiji tropical dry forests occupy the leeward, northwestern lowlands of Viti Levu and Vanua Levu, the two largest islands of Fiji, extending onto smaller islands in the Yasawa and Lau groups. Their canopy is typically dominated by Dacrydium nidulum and Fagraea gracilipes, with Garuga floribunda and Gyrocarpus americanus prevailing in the driest sites, alongside the cycad Cycas seemannii and the endemic sandalwood Santalum yasi. Sitting in the rain shadow of the islands' central mountains, the climate is tropical and strongly seasonal, with most rain falling between December and April and a long dry season that gives the trees a shorter, gnarled, vine-draped character; tropical cyclones occasionally strike from November to April. These are among the most endangered forests in the Pacific, with much of the original cover long ago burned and cleared into sparse grass-fern talasiga savanna, leaving only a small fraction protected. The ecoregion is the flagship habitat of the Fiji crested iguana and supports a flora that is overwhelmingly endemic to the archipelago. For gardeners, the native sandalwood Santalum yasi is a notable regional genus prized for its fragrant heartwood.

The Hawaiʻi tropical dry forests cover the leeward, rain-shadowed sides of the main Hawaiian Islands, along with the summits of Niʻihau and Kahoʻolawe, where the central ranges and large volcanoes strip moisture from the trade winds before it reaches the lowlands and foothills. These dry broadleaf forests are built around drought-adapted native trees including koa and koaiʻa (Acacia), ʻōhiʻa lehua (Metrosideros polymorpha), māmane (Sophora chrysophylla), lama (Diospyros sandwicensis), wiliwili (Erythrina sandwicensis), loulu fan palms (Pritchardia), and the sandalwoods or ʻiliahi (Santalum). The climate is markedly seasonal, with a long dry season and rainfall that is low for the tropics, ranging from roughly 25 to 125 centimeters a year. Despite their modest extent, these forests are botanically rich, holding about 22 percent of Hawaiʻi's native flora with most of those taxa found nowhere else, and they shelter the palila, a Hawaiian honeycreeper restricted to māmane-dominated dry forest. They rank among the most endangered ecoregions on Earth, with only an estimated 5 to 8 percent of natural habitat remaining. For gardeners, several of these natives such as wiliwili and the loulu palms are grown ornamentally in dry, sunny landscapes.

The Marianas tropical dry forests stretch across Guam and the Northern Mariana Islands, both United States jurisdictions strung along a roughly 900-kilometer arc in the western Pacific Ocean. The terrain mixes young volcanic islands in the north with older southern islands built of volcanic rock and raised marine limestone, including limestone-capped Guam. Vegetation ranges from coastal stands of ironwood (Casuarina equisetifolia), Pisonia grandis, pandanus, and the fern Nephrolepis hirsutula to limestone forests of native breadfruit (Artocarpus mariannensis), the banyan fig Ficus prolixa, and Cordia subcordata, with volcanic-soil broadleaf forests dominated by Aglaia mariannensis and Elaeocarpus joga. The climate is warm and strongly seasonal, with annual rainfall around 2,000 to 2,500 millimeters and a wet season running from July through October, while frequent strong typhoons shape a dense, vine-laden forest structure with few emergent trees. The islands harbor endemic wildlife such as the flagship Mariana fruit dove and the Mariana flying fox, though invasive species, above all the brown tree snake blamed for extinctions of native birds on Guam, remain the foremost conservation threat.

The Apure-Villavicencio dry forests stretch along the eastern foot of the Andes' eastern cordillera, spanning the Venezuelan states of Portuguesa, Barinas and Apure and the Colombian departments of Arauca, Casanare and Meta. This is a transitional ecoregion, a patchwork of premontane, gallery and deciduous dry forest grading into savanna where the Andean montane forests give way to the lowland Llanos grasslands. Characteristic woody plants include mesquite (Prosopis juliflora), palo verde (Cercidium praecox), kapok (Ceiba pentandra), yellow mombin (Spondias mombin), and palms such as the moriche (Mauritia flexuosa) and macaúba (Acrocomia aculeata). Its climate is equatorial with a pronounced dry winter (Köppen Aw), with temperatures ranging from about 19 to 33 degrees Celsius. The forests have been severely degraded by deforestation, farming and ranching, leaving poorly protected remnants that the World Wildlife Fund rates as Vulnerable, yet they still shelter the giant anteater, Geoffroy's spider monkey, and the flagship Colombian four-eyed frog. Gardeners may recognize several natives here as ornamentals, including the stately kapok tree and the moriche and macaúba palms.

The Bajío dry forests cover the southwestern Mexican Plateau in west-central Mexico, spanning the states of Jalisco, Guanajuato, and Michoacán across the Lerma River basin and the lake country around Chapala, Cuitzeo, and Pátzcuaro. Set in valleys between roughly 1,000 and 2,000 meters on shallow, rocky, well-drained volcanic and limestone soils, the region was historically dry deciduous forest whose characteristic trees included copal, pochote, palo amarillo, and mauto, with thorn-scrub communities of mesquite and huamúchil. The climate is tropical subhumid, with annual rainfall around 500 to 930 millimeters and a pronounced dry season that can last up to eight months. This is one of Mexico's most developed and densely populated landscapes, and centuries of agriculture and grazing have reduced the forest to small pockets now dominated by thorn scrub and subtropical matorral, leaving the ecoregion classed as critical or endangered with only about 7.5 percent in protected areas. Gardeners working in comparably dry, seasonal climates may recognize natives of this region in drought-adapted, deciduous trees such as mesquite and copal.

The Balsas dry forests occupy the basin of the Balsas River in western and central Mexico, spreading across the states of Michoacan, Guerrero, Morelos, Mexico, Puebla, and Oaxaca. This tropical dry broadleaf ecoregion is a deciduous and thorn forest dominated by Bursera trees, alongside the legume Haematoxylum brasiletto and abundant columnar cacti such as Pachycereus and Cephalocereus. The climate is tropical and subhumid, with seasonal rainfall and a severe dry season that can last up to eight months. The forests are a renowned center of plant endemism and speciation, especially for Bursera, with roughly half of the region's Bursera species found nowhere else, and they shelter the near-endemic Balsas screech-owl, though only about a tenth of the ecoregion lies within protected areas. For drought-tolerant or xeric plantings, the native Bursera (the source of copal incense) and the dyewood Haematoxylum brasiletto are ornamental genera that evolved here.