Fire drives functional thresholds on the savanna-forest transition

Area of Science:

• Tropical ecology
• Plant-fire ecology
• Community dynamics

Background:

• Tropical landscapes exhibit mosaics of vegetation with varying tree densities.
• Climate models alone cannot predict these vegetation patterns.
• Plant-fire feedbacks are hypothesized to maintain savanna and forest as distinct stable states.

Purpose of the Study:

• To provide field evidence for the plant-fire feedback threshold model in tropical landscapes.
• To analyze the functional and phylogenetic consequences of fire in the Brazilian Cerrado.
• To test if savanna and forest states exhibit abrupt changes in attributes along a community closure gradient.

Main Methods:

• Established 98 plots along a savanna-to-forest gradient in the Brazilian Cerrado.
• Assessed nine functional traits, five soil features, and seven diversity indicators.
• Analyzed for threshold patterns and their association with different fire regimes.

Main Results:

• Most community attributes showed a threshold pattern at the savanna-forest transition.
• Two distinct states were identified: open savannas (low diversity, poor soils, fire-resistant plants) and closed forests (high diversity, fertile soils, shade-tolerant plants).
• Each state was associated with contrasting fire regimes.

Conclusions:

• Results support the hypothesis that savannas and forests are stable states maintained by plant-fire feedbacks.
• Fire plays a crucial role in regulating the distribution and characteristics of these tropical biomes.
• Contrasting functional and diversity patterns are regulated by fire-plant interactions.