WWF (World Wildlife Fund) began publishing its Living Planet Reports since 1998, to update us on the changing state of the earth’s biosphere because of human impact.

There are two major components in the latest report, released in 2006. The first one reflects the health of the planet’s ecosystems, which is measured by the living planet index. The second component shows the extent of human demand on these ecosystems, and is measured by the ecological footprint.

Here I summarize the results for the living planet index.

Living Planet Index (LPI)

LPI tracks over 3600 populations of 1313 vertebrate species - fish, birds, reptiles, amphibians and mammals - from all across the globe. Of them, 695 are terrestrial (living on land) species, 274 marine (ocean-dwelling), and 344 freshwater (living in rivers, lakes, streams and wetlands) species.

Accordingly, three separate indices are estimated, for terrestrial, marine and freshwater species, and the overall LPI is then calculated as the average of these three indices. The LPI shows a decline of about 30% over the 33-year period from 1970 to 2003 (see the picture).

Below is a summary of the three component indices.

Terrestrial Species. The terrestrial LPI has declined around 30% between 1970 and 2003. Among the species considered, populations of tropical species showed a 55% decline, whereas the temperate species held relatively steady.

This high rate of decline in tropics is because of the loss of natural habitat to cropland and pasture between 1950 and 1990. By contrast, in temperate zones the agricultural conversion of habitats was mostly over before 1950, and wild populations stabilized soon thereafter.

Marine Species. The marine LPI is divided by the Pacific Ocean, Arctic/Atlantic Ocean, Indian/Southeast Asian Ocean, and Southern Ocean (seas around Antarctic). The index shows over 25% decline across all four ocean basins.

Pacific and Arctic/Atlantic Oceans show relatively stable trends, where increasing populations of sea birds and some mammal species since 1970 mask a decline in many commercially important fish stocks, such as cod and tuna, because of overfishing, and also turtles and other species lost to bycatch.

By comparison, Indian/Southeast Asian and Southern Oceans show dramatic decline. This is because of the rapid loss of Mangrove habitats, which are saltwater-tolerant, inter-tidal forests along tropical shorelines, and provide food and shelter to 85% of the commercial fish species in the tropics.

Freshwater species. The freshwater LPI of 344 species (of which 287 live in temperate zones and 51 in tropics) declined an average 30% between 1970 and 2003. Freshwater bird populations stayed relatively stable, whereas other freshwater species declined by about 50% over this time.

Habitat loss, overfishing, invasive species, pollution, and disruption of river systems for water supply are among the main drivers of this decline. Damming of rivers for industrial and domestic use, irrigation and hydroelectric power have fragmented over half of the world’s river systems, thus affecting the productivity of wetlands, flood plains, and deltas, and disrupting fish migration.