Thresholds Database > Grassland to woodland, Serengeti-Mara, Tanzania

Background

Alternate Regimes

1. Grassland

2. Woodland

Mechanism

State 1: Prior to 1890, a grassland state dominated due to a high density of herbivores, which browsed on the seedlings of woody vegetation inhibiting their regeneration.

Switch from State 1 to State 2: In the 1890's, rinderpest disease and ivory hunting greatly reduced herbivore numbers. This enabled the regeneration of woody shrubs.

Switch from State 2 to State 1: In the early 1960's, high rainfall and low herbivore numbers enabled high grass growth, which supported frequent and severe fires. Many of the low shrubs and seedlings were killed. In the 1980's, the remaining aged woodland died and a high density of elephants browsed on the seedlings of the woody vegetation inhibiting their regeneration and the system returned to grassland.

Management Decisions in Each Regime

State 1: With a large human population increase and an expansion of cultivation and settlement in the latter half of the 20th century, elephants were moved into the protected reserves. This created unusually high concentrations of elephants in these areas. Elephant numbers are kept at approximately 1000 to promote elephant conservation and encourage tourism. The system is therefore likely to stay in the grassland state (State 1).