An experimental investigation of the resistance of model root systems to uprooting

Abstract

The architecture of a tree root system may influence its ability to withstand uprooting by wind loading. To determine how the root branching pattern may alter the anchorage efficiency of a tree, artificial model root systems with different topologies and branching angles were built. The root systems were embedded at various depths in wet sand and the pull-out resistance measured. A model to predict the uprooting resistance from the data collected was designed, allowing predictions of anchorage strength with regards to architecture. The dominant factors influencing pull-out resistance were the depth and length of roots in the soil. The most efficient type of branching pattern predicted by the program was one with an increased number of roots deep in the soil. The optimum branching angle most likely to resist pull-out is a vertical angle of 90° between a lateral and the main axis. The predicted mechanically optimal radial angle between a lateral branch and its daughter is between 0 and 20°. Values of branching angle are compared with those measured in real woody root systems of European latch and Sitka spruce.