Changing the narrative: encroached savannas are not forest

Catherine L Parr, Richard Bardgett, James M. Bullock, Caroline Lehmann

1. Savannas are globally important ecosystems but are often misclassified as forests because they can support high tree cover, leading to misguided management. This misunderstanding arises because the presence of grasses, a key defining component of savannas, critical for their structure and functioning, is overlooked.
2. Fundamental tree-based misunderstandings affect the interpretation of woody plant encroachment, a novel threat facing savannas, which now affects more than 5 million km² of savanna globally. High tree cover can degrade savannas by reducing grasses, altering fire regimes, and harming biodiversity and livelihoods.
3. We highlight that savannas can naturally vary in woody cover, and therefore high tree cover does not necessarily equate to an encroached state. We also clarify that even in an encroached state, high tree cover does not necessarily create forests. We identify three end-states, determined by rainfall and proximity to true forest, that may emerge as an outcome of encroachment: encroached, novel savanna, hybrid forest and true forest.
4. Synthesis Forests should not be viewed as superior to savannas. Savannas are biodiversity hotspots and vital for human survival. Effective management requires moving beyond structural definitions, understanding thresholds, and assessing ecosystem value based on biodiversity and function, not tree cover alone.