Terrestrial ecosystems extend over little more than one quarter of the Earth's surface but they are more accessible than aquatic habitats and so are far better known. The land supports fewer phyla than the oceans but most of the global diversity of species, and is characterised above all by an extensive cover of vascular plants, with associated animals and other groups of organisms.

Forest and woodland ecosystems form the predominant natural land cover over most of the Earth's surface. These systems generate around half the terrestrial net primary production, and forests in the tropics are believed to hold most of the world's species. Approximately half the area of forest developed in post-glacial times has since been cleared or degraded by humans, and the amount of old growth forest continues to decline.

Grassland, shrubland and deserts collectively cover most of the unwooded land surface, with tundra on frozen subsoil at high northern latitudes. These areas tend to have lower species diversity than most forests, with the notable exception of Mediterranean-type shrublands, which support some of the most diverse floras on earth.

Humans have extensively altered most grassland and shrubland areas, usually through conversion to agriculture, burning and introduction of domestic livestock. They have had less immediate impact on tundra and true desert regions although these remain vulnerable to global climate change.