Tree Root Response to Mechanical Stress
Until recently, the role of the root system, with regards to tree stability, has been neglected. However, due to the increasing number of storms in Europe over the past years, research into tree anchorage has begun to be investigated.
As the form and strength of a root system influences the stability of a tree, how is it affected by external mechanical factors? Studies carried out during the last thirty years have shown that mechanically stressed woody roots develop large, eccentrically formed root bases. However, recent work has shown that windward and leeward roots of Picea sitchensis, grown in wind tunnels, were also found to be more numerous, with highly branched windward roots.
Bending and compression strength tests carried out on the rootwood of several mature tree species showed that the strength of the rootwood was correlated with the shape of the root system. Strength was found to be higher in areas of greatest stress i.e. the under sides of lateral roots, where the roots are pushed downwards onto the soil, and parts of the root system which sway the most under wind loading. This increase in strength appears to correspond to a change in the rootwood anatomy, as cells in these regions become more dense with thicker walls and an increased microfibri angle.
It appears that root systems can adapt to imposed mechanical stresses. However, the intrinsic form of a tree root system is a factor which must also be taken into account when considering the stability of a tree. We need to combine this knowledge in order to determine the mechanically optimal form of a tree root system and how it can be manipulated in order to improve tree stability.
KeywordsRoot System Wind Tunnel Lateral Root Specific Gravity Radial Growth
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