Anaïs Gorel, University of Liège, Gembloux Agro-Bio Tech in Belgium, discusses their article: Leaf habit, maximum height, and wood density of tropical woody flora in Africa: phylogenetic constraints, covariation, and responses to seasonal drought
How do African trees cope with drought?
Tropical Africa is home to a remarkable diversity of trees, ranging from towering giants in dense rainforests to smaller, more resilient species in dry savannas. But how have these trees evolved to survive in such a varied climate, especially in a region that experiences more dryness and seasonal variation compared to other tropical areas? We sought to shed light on this question by examining three key traits that influence how trees cope with drought: leaf habit (evergreen vs. deciduous), maximum tree height, and wood density.
Exploring tree traits related to drought strategies
To understand how trees in Africa’s forests and savannas respond to seasonal drought, we compiled a large database of over 1,300 species. We analysed whether trees retain their leaves year-round or shed them during dry periods, how tall they grow, and how dense their wood is. We also explored how these traits are influenced by climate and evolutionary history.
Using Bayesian phylogenetic models, we tested whether closely related species share similar drought strategies and whether climate alone could predict these traits. Our findings reveal a complex interaction between evolutionary history, climate, and trait covariation.
Key findings: The role of evolutionary legacy and climate in trait covariation
One of our most striking discoveries is that evolutionary history plays a significant role in shaping tree traits. Leaf habit and a species’ affinity to forests or savannas show a strong phylogenetic signal, meaning that closely related species tend to share these characteristics. However, we also found that major evolutionary shifts have allowed trees to adapt to different environments over time.
Interestingly, climate alone was a poor predictor of wood density and could not fully explain leaf habit or maximum tree height. Instead, trait interactions were more influential, such as in the forest biome, where small understory species were more likely to be evergreen and have dense wood, while taller canopy species tended to be deciduous and have lighter wood. In wetter forests, both evergreen and deciduous species coexisted in the canopy, highlighting the complexity of tree responses to climate.
