The Hawaiian tropical dry forests are a tropical dry broadleaf forest ecoregion in the Hawaiian Islands.
 They cover an area of 6600 km2 on the leeward side of the main islands and the summits of Niʻ ihau and Kahoʻ olawe.
 These forests are either seasonal or sclerophyllous.
 Annual rainfall is less than 127 cm and may be as low as 25 cm ; the rainy season lasts from November to March.
 Dominant tree species include koa ("Acacia koa"), koaiʻ a ("A. koaia"), ʻ akoko ("Euphorbia" spp.)
, ʻ ōhiʻ a lehua ("Metrosideros polymorpha"), lonomea ("Sapindus oahuensis"), māmane ("Sophora chrysophylla"), loulu ("Pritchardia" spp.)
, lama ("Diospyros sandwicensis"), olopua ("Nestegis sandwicensis"), wiliwili ("Erythrina sandwicensis"), and ʻ iliahi ("Santalum" spp.)
.
 Endemic plant species in the dry forests include hau heleʻ ula ("Kokia cookei"), uhiuhi ("Caesalpinia kavaiensis"), and "Gouania" spp.
 The palila ("Loxioides bailleui"), a Hawaiian honeycreeper, is restricted to this type of habitat.
A Dry Forest are defined as a community of trees of different species that coexist in the same environment.
 These trees can grow nearby forming a canopy above.
 Dry forests lack an abundance of moisture, yet, there is an adequate amount of moisture to sustain the growth of the forest.
 Although dry forest tends to grow at an intermediate height compared to moist forest.
 Dry forest receives 850-1100mm of precipitation per year.
 High quantities of sea salt from the ocean decreases the height of the trees.
 Dry forest also consisted of layers of canopies, specifically two canopy layers that commonly found at an elevation below 300 meters.
 There is limited dead dry wood for termites to consume, this correlates with low density of termites in dry forests.
 The characteristics and development of Virgin Islands Dry Forest are contributed by a unique wind pattern that is usually strong.
 Dry Forest usually thrive in environments that have plenty sunshine, steep slopes, on soil that are challenged by thin rocky layers that poorly absorbs water.
 Within the three islands in the United States Virgin Islands, St. John has maintained a higher percentage of dry forest cover competing with St. Thomas at 43.1%; St. Croix has limited dry forest cover (9.22%).
 St. John and St. Thomas topography has significant steep hills and slopes compared to St. Croix.
 St. John is the most protected of the three islands, and as such it has the largest extensive tropical dry forests in the U.S. Virgin Islands.
 The island contains 650 native plants, 5,000 or more terrestrial insects, over 180 species of birds, of which 90% are native, and six native mammal bat species.
 One of the most common trees in the “native dry forest garden” is the amarat.
 They are acacias, (casha bush) but do not have thorns likes most other varieties.
Wiliwili, with the scientific name Erythrina sandwicensis, is a species of flowering tree in the pea family, Fabaceae that is endemic to the Hawaiian Islands.
 It is the only species of "Erythrina" that naturally occurs there.
 It is typically found in Hawaiian tropical dry forests on leeward island slopes up to an elevation of 600 m .
The tailless tenrec ("Tenrec ecaudatus"), also known as the common tenrec, is a species of mammal in the family Tenrecidae.
 It is the only member of the genus Tenrec.
 Native to Madagascar, it is also found in the Comoros, Mauritius, Réunion, and Seychelles, where it has been introduced.
 Its natural habitats are subtropical or tropical dry forests, subtropical or tropical moist lowland forests, subtropical or tropical moist montane forests, dry savanna, moist savanna, subtropical or tropical dry shrubland, subtropical or tropical moist shrubland, subtropical or tropical high-altitude shrubland, subtropical or tropical dry lowland grassland, subtropical or tropical high-altitude grassland, arable land, pastureland, plantations, rural gardens, and urban areas.
The striped tree frog (Hypsiboas caingua) is a frog species in the family Hylidae found in Argentina, Brazil, and Paraguay.
 Its natural habitats are subtropical or tropical dry forests, subtropical or tropical moist lowland forests, subtropical or tropical dry lowland grassland, subtropical or tropical seasonally wet or flooded lowland grassland, rivers, swamps, heavily degraded former forests, and ponds.
 It is not considered threatened by the IUCN.
Calaby's pademelon ("Thylogale calabyi"), also known as the alpine wallaby, is a species of marsupial in the family Macropodidae.
 It is endemic to Papua New Guinea.
 Its natural habitats are subtropical or tropical dry forests, dry savanna, subtropical or tropical dry shrubland, and subtropical or tropical dry lowland grassland.
 It is threatened by habitat loss.
The greater hedgehog tenrec or large Madagascar hedgehog or sokina ("Setifer setosus", formerly known as Dasogale fontoynonti) is a species of mammal in the family Tenrecidae.
 It is endemic to Madagascar.
 Its natural habitats are subtropical or tropical dry forests, subtropical or tropical moist lowland forests, subtropical or tropical moist montane forests, dry savanna, moist savanna, subtropical or tropical dry shrubland, subtropical or tropical moist shrubland, subtropical or tropical high-altitude shrubland, subtropical or tropical dry lowland grassland, subtropical or tropical high-altitude grassland, rural gardens, urban areas and zoos.
The Hottentot golden mole ("Amblysomus hottentotus") is a species of mammal in the golden mole family, Chrysochloridae.
 It is found in South Africa, Swaziland, and possibly Lesotho.
 Its natural habitats are temperate forests, subtropical or tropical dry forests, subtropical or tropical moist lowland forests, dry savanna, moist savanna, subtropical or tropical dry shrubland, Mediterranean-type shrubby vegetation, temperate grassland, subtropical or tropical dry lowland grassland, subtropical or tropical high-altitude grassland, sandy shores, arable land, pastureland, plantations, rural gardens, urban areas, and introduced vegetation.
The dusky pademelon or dusky wallaby ("Thylogale brunii") is a species of marsupial in the family Macropodidae.
 It is found in the Aru and Kai islands and the Trans Fly savanna and grasslands ecoregion of Papua Province of Indonesia, and Papua New Guinea.
 Its natural habitats are subtropical or tropical dry forests, dry savanna, subtropical or tropical dry shrubland, and subtropical or tropical dry lowland grassland.
 It is threatened by habitat loss.
Acacia koa is a species of flowering tree in the pea family, Fabaceae.
 It is endemic to the Hawaiian Islands, where it is the second most common tree.
 The highest populations are on Hawaiʻ i, Maui and Oʻ ahu.
 Its name in the Hawaiian language, koa, also means brave, bold, fearless, or warrior.

Question: Hawaiian tropical dry forests have a dominant tree species of which tree in the pea family?
Answer: Acacia koa