Why savanna trees sometimes cluster and at other times not

What is it about?

Spatial distribution of woody individuals (shrubs, trees) is highly variable in African savanna ecosystems. We studied whether woody species were more or less clustered than expected based on random patterns and investigated which factors affected this spatial organization. We found that under dry conditions trees are spread out more evenly across the landscape and that fire is related to tree clustering. This suggest that under low rainfall conditions trees compete for water, while under high fire frequencies they facilitate each other through protection against fire.

Why is it important?

Spatial organization in natural ecosystems are important as they influence ecosystem functioning and stability. Furthermore they can be used to predict underlying dominant processes. In savanna ecosystems, woody individuals face three major constraints: drought, fire and herbivory. Our study suggest that drought and fire have opposite effects on the spatial organization of trees/shrubs and therefore the spatial organization can be used to predict whether in specific areas low rainfall or fire is a more important constraint of woody cover.