Biodiversity: Tropical vs Temperate

Biodiversity trends in tropical and temperate areas are starkly different.

The animal populations tracked by the global Living Planet Index can be divided into those living in the tropics and those living in temperate regions.
Natal forest treefrog (Leptopelis natalensis), tropical southeast Africa ; alpine marmot (Marmota marmota), Austria
© Martin Harvey / Anton Vorauer / WWF
Figure 6: The Temperate LPI & the Tropical LPI The temperate index shows an increase of 29% between 1970 and 2007. The tropical index shows a decline of more than 60% between 1970 and 2007. LPR2010
This difference is seen for mammals, birds, reptiles, amphibians and fish, as well as for for land, marine and freshwater species. 

What is the reason for this difference?

Tropical and temperate areas have seen different rates and timing of habitat loss.

The major cause of biodiversity loss in recent times is habitat destruction and degradation. This is mostly caused by land-use changes, such as clearing forests and other habitats for agricultural land, plantations, and urban areas.

Temperate areas had already lost over half their broadleaf forests by 1950. In contrast, deforestation only accelerated in the tropics after 1950. Although data are not available, the same trend is likely for other habitat types.

The temperate LPI likely starts from an already reduced baseline.
Many animals living in temperate areas probably felt the impact of agricultural expansion and industrialization long before the beginning of the LPI in 1970.

If we had enough data to extend this index back for centuries, then we would probably see a long-term decline at least as great as that seen in the tropical LPI.

The temperate LPI increase since 1970 may be due to better environmental management in recent decades that has allowed animal populations to recover. This includes better pollution control and waste management, better air and water quality, an increase in forest cover and/or greater conservation efforts in at least some temperate regions.

The tropical LPI likely starts from a higher baseline.
The rapid decline in the tropical LPI reflects the large-scale land-use changes that have continued in tropical regions since the start of the index in 1970. The damaging impacts of these changes on tropical species overall outweigh any positive conservation impacts.
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