Background/Question/Methods
- Dimensions of tree root systems in savannas are poorly understood, despite being essential in resource acquisition and post-disturbance recovery.
- We studied tree rooting patterns in Southern African savannas to ask (1) how tree rooting strategies affected species responses to severe drought, and (2) how rooting depths varied across gradients in soil texture and rainfall.
- Detailed excavations of 8 species in Kruger National Park suggest that the ratio of deep to shallow taproot diameters provides a reasonable proxy for rooting depth, facilitating extensive inter-specific comparisons across Southern African savannas.
Results/Conclusions
- Results from Kruger National Park indicated that allocation to deep roots traded off with shallow lateral root investment. Drought-sensitive species rooted more shallowly than drought-resistant ones.
- Across 57 species in Southern Africa, rooting depths were phylogenetically constrained, with investment to deep roots evident among miombo Detarioids, consistent with results suggesting they green up before onset of seasonal rains.
- Soil substrate also explained variation, with deeper roots on sandy, nutrient-poor soils relative to clayey, nutrient-rich ones. Curiously, rainfall had no systematic effect on rooting depth.
- Overall, our results suggest that rooting depth systematically structures the ecology of savanna trees. Further work examining other anatomical and physiological root traits should be a priority for understanding savanna responses to changing climate and disturbances.