Around 1400 the Easter Island palm became extinct due to over-harvesting. Its capability to reproduce has become severely limited by the proliferation of rats, introduced by the Islanders when they first arrived, which ate its seeds...The Islanders, no longer with the palm wood needed for canoe building, could no longer make journeys out to sea. Consequently, the consumption of land birds, migratory birds, and molluscs increased. Soon land birds went extinct and migratory bird numbers were severely reduced, thus spelling an end for Easter Island's forests. Read more...
One set of hypotheses, summarized in the book "Collapse", impute deforestation to direct and indirect human behaviour. Humans cleared actively the entire forest and hunted the local fauna until the brink of extinction. In a modified version of the human-impact hypothesis, the colonists were not the main and only culprits of the environmental collapse, but invasive plant or animal species brought by them on the isolated island, which in fierce concurrence with native species caused their rapid decline and extinction.
A second set of hypotheses deal with a possible massive impact of past climate changes, like prolonged droughts, on an already sensible and unstable island environment and society. Read more...