At the beginning of the Holocene, around 12,000 years ago, the vast majority of terrestrial and marine systems were barely impacted by humans. Today, there is arguably no ecosystem on earth that is not impacted by humans to some degree. All ecosystems are affected by anthropogenic climate change. Most have been altered by changes in land use and land cover, or have been impacted by the off-site effects of such changes. Of the fourteen major terrestrial biomes only tundra and boreal forests have been left relatively intact. All others have been transformed to some degree, and in six (temperate grasslands, Mediterranean forests, tropical dry forests, temperate broadleaf forests, tropical grassland, and flooded grasslands) the area converted to agriculture, forestry, or urban industrial, commercial, domestic, or other activities currently lies somewhere between a half and two-thirds (Millennium Ecosystem Assessment 2005a). Much of the earth’s biodiversity now lies outside natural systems, in systems created or at least heavily impacted by people.
The term biodiversity refers to the diversity of genes, species, and ecosystems (Wilson 1988). Many people use the term in a more restricted way to mean the diversity of species in wildlands, but it goes far beyond that. It encompasses the variety of species used in human production and consumption activities: the food we eat, the biologically derived fuels and fibers that support production of a wide range of commodities, and the varying landscapes that we access for inspiration, recreation, and learning. It encompasses the genetic diversity of cultivated crops, of crop pests, of wild crop relatives, and of weedy species. It encompasses the range of diseases that affect humans, animals, and plants, and the species used to counter those diseases – traditional medicinal plants and the plants used as the source of modern pharmaceuticals. It encompasses the species that underpin biotechnology-based industries as well as those that support more traditional forestry and fisheries.