African shrub distribution emerges via a trade-off between height and sapwood conductivity

Aim Shrubs are multistemmed woody plants and are a successful growth form in many ecosystems globally. Ecosystems such as the Fynbos in South Africa or mediterranean shrublands are dominated by a dense shrub cover. In savannas, shrubs are a major vegetation component. Despite the importance of shrubs at the global scale, they are, in contrast to trees, often understudied both in empirical and modelling studies. We define shrub and tree strategies by a trade-off between water uptake capacity and height growth, and aim to explore if this trade-off allows us to explain shrub distribution. Location Methods Sub-Saharan Africa We improve a dynamic vegetation model, the adaptive Dynamic Global Vegetation Model version 2 (aDGVM2), to simulate shrubs as multistemmed woody plants, based on a trade-off between rapid height growth in single-stemmed trees and efficient water uptake in multistemmed shrubs. Results Main conclusion We show that, in aDGVM2, (a) the implemented trade-off allows a multistemmed shrub strategy to emerge and is sufficient to simulate the broad distribution of shrubs in African savannas; (b) fire and aridity promote shrubs at the expense of trees and grasses; and (c) the presence of shrubs influences competitive interactions between grasses and woody vegetation. We provide a novel approach to simulate shrubs in a dynamic vegetation model. This approach enhances our understanding of the distribution of shrubs, but further work is required for arid and mediterranean shrublands. We conclude that introducing fundamental trade-offs between growth forms into vegetation models can improve vegetation representation.