Green Island is 90 ha with a maximum elevation of 7.3 m and a mean elevation of 2.8 (SD 2.0). The island provides nesting habitat for 18 species of seabirds and is one of the six major breeding sites for the endangered Hawaiian monk seal (Monachus schauinslandi). The emergent reef, which provides protection from large swells and resting habitat for monk seals, also dispenses energy and nutrients into the atoll supporting a shallow reef ecosystem. The outer slopes of the atoll provide deeper habitat for coral colonies, all of which exist near the “Darwin Point” where ocean temperatures fall below physiological optimum for reef building corals. The lagoon offers additional habitat for reef development, fish recruitment, daily resting habitat for spinner dolphins (Stenella longirostris), and foraging habitat for species such as Galapagos sharks (Carcharhinus galapagensis), tiger sharks (Galeocerdo cuvier), spotted eagle rays (Aetobatus narinari), ulua (Carangidae sp.) and the threatened Green Sea Turtle (Chelonia mydas).
A short visit by a naturalist in 1915 and a more thorough visit during the Tanager Expedition of 1923 provided the first systematic inventory to the island’s flora and fauna (Christophersen and Caum 1931). At the time, there were 13 native species documented.
The island’s vegetation was described as being densely dominated by Naupaka (Scaevola sericea) with an open plain of ca. 8-10 hectares toward the east-central part of the island. The central part of the island was described as diverse, low-lying vegetation dominated by Tribulus cistoides, Ipomoea spp., and Eragrostis variabilis with a few rare plants interspersed (e.g. Solanum nelsonii, Lipochaeta integrifolia) found nowhere else on the island. The central plains were also described as being “honeycombed” with petrel burrows and were observed to support the only nesting masked and brown boobies on the island.
By 1961, the first non-native plant species were documented and likely introduced during the construction of radar reflector built by the US Navy in 1955. Among the plants introduced was the invasive species Verbesina encelioides.
The Coast Guard made further alterations by constructing a runway and several buildings on Kure and began to occupy the island in 1960. One year later, Lamoureux (1961) reported that all 13 vascular plants collected in 1923 by the Tanager Expedition were still present along with one undocumented endemic species. He also discovered 22 species of newly introduced weeds and cultivated plants but commented that indigenous plants were abundant and not in immediate danger.
In 1968, only 9 years after V. encelioides was discovered on the island, it was documented as “widespread and growing in most of the open areas mainly in the central plain and near the radar reflector. It grows in dense stands up to four feet tall and is a potential danger to the island's ecosystem” (Woodward 1972).
Rarer native plants started to disappear in 1979. Three native plants were extinct by 1992 and an added three by 2002.