Savannah

A savannah (or savanna) is a mixed woodland-grassland ecosystem characterised by open canopies that permit sufficient light to reach the ground to support an unbroken herbaceous layer. The distinction between savannah and forest is not merely botanical — it is a tipping point in the Earth system, maintained by feedbacks between vegetation, climate, and fire regimes.

The term has become urgent in climate science because of the risk of Amazon savannification: the conversion of tropical rainforest to savannah through the interaction of deforestation, rising temperatures, and altered rainfall patterns. The Amazon generates approximately half of its own rainfall through transpiration; as forest cover declines, less moisture is recycled, rainfall decreases, and the conditions favouring savannah expand. Research suggests a critical threshold at 20–25% deforestation, beyond which the system may reorganise irreversibly into a drier state.

Savannahs are not degraded forests. They are stable alternative states maintained by distinct feedback structures: grass-fuelled fire regimes that prevent tree recruitment, herbivore grazing that suppresses woody encroachment, and seasonal drought that selects for drought-adapted species. The mistake — common in restoration ecology — is to treat savannah as a failed forest. It is not. It is a different attractor in the same dynamical system, and the transition between them is not gradual but bifurcational.