Plasticity of tree root system structure in contrasting soil materials and environmental conditions

Abstract

Methods: Two hundred and forty-three mature trees from 12 species were uprooted from homogeneous French dikes fills. Root system structure (root number and size, root system span, depth and volume) was compared between two contrasting soil materials: fine and coarse. Background and aims: Tree root system structure and development are difficult to assess and poorly understood in natural conditions because of soil heterogeneity and the difficulty in extracting mature tree root systems without damaging them. The purpose of this study was to understand root system development plasticity according to biological and physical parameters: species, tree age and size, soil material, water availability, slope angle, and climate. Results: Tree species had little influence on root system structure: all root system types and root size could be found for most of the species according to site conditions. Heart root systems were limited to fine material while mixed and tap root systems were found on coarse material. In coarse materials, trees developed few but rather large roots (>5 cm in diameter and >4 m in length). In fine materials, root systems had three times more roots but they were 40 % smaller and shorter. Roots were 20 % more numerous and 65 % larger on the downslope side due to water availability at dike or riverbank toe. Conclusion: Root system structure was mainly influenced by soil material and water availability and far less by tree species. Tree root systems are opportunistic in developing in the direction where water and nutrients are plentiful: whatever the species, predicting its dimensions and structure requires a thorough investigation of soil and other environmental conditions. This study gives a new insight in root development: it will help predict tree root growth in various environments and particularly on dikes.