A number of plant species are now extinct due to grazing livestock, and aggressive non-indigenous species taking over the land. Almost 40% of the endangered species in the United States are Hawaiian species, while nearly 75% of all U.S. extinctions have occurred in Hawaii.
The native flora comprises 89% endemic species, but the flora of Hawaii now includes more than 1044 introduced plant species; more than 100 of these are likely to be invasive in natural areas. Species such as the strawberry guava (Psidium cattleianum), and christmasberry(Schinus terebinthifolius) have spread across wide areas, competing with native species and altering the natural ecosystem. Recent invaders like miconia or velvet tree (Miconia calvescens) and Himalayan raspberry (Rubus ellipticus) are now permanently established over large areas. These species are predicted to decrease watershed function.
Prior to the arrival of non-natives, some bird species were made extinct, or pushed to near extinction from the collection of feathers by Native Hawaiians. With the arrival of James Cook in 1778, a new set of environmental threats emerged. Alien species such as cats, dogs, rabbits, pigs, and rats affected a number of indigenous species. Hawaii is known as the "extinction capital of the world" with the extinction of nearly half (140) of its historically recorded native bird species. Some of the alien species that are currently affecting Hawaii include cane toads,mongoose, coquí frogs, gall wasps, Mediterranean, Oriental, and melon flies that damage crops, ants that destroy native insects, and bacteria that infect waters.