Land
We know more about the biodiversity on land than in any other environment.
Forests and woodlands hold more biodiversity than any other land-based
habitat. In fact, tropical rainforests hold most of the world's known species
(though some scientists believe soils beneath savannahs are as diverse).
The rainforests are threatened by deforestation and development. Approximately half the forests that developed since the last ice age have been cleared or degraded by people, creating serious strains on these ecosystems.
Grassland, open shrubland, desert and tundra tend to have fewer species than most forests. Notable exceptions are Mediterranean-type shrublands, which support a huge variety of plants.
We have changed most grassland areas by growing crops and grazing livestock.
One handful of soil contains more individual micro-organisms than the total number of people who have ever lived on Earth.
Micro-organisms, including bacteria and fungi, turn nitrogen from the air into nutrients for plants, recycle nutrients, break down wastes, and deal with toxins.
New DNA techniques mean scientists can identify what organisms are present by screening soil samples for DNA. Scientists can also search for particular functions, such as the ability to remove toxic metals, by checking that certain genes are present.