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Hazard Assessment

Root and soil factors. Show Larger Image
Root and Soil Factors

What impact does soil type have on windthrow hazard?

Strength of anchorage is a function of root/soil mass, root/soil bond or shallow soils and drainage.

The diagnostic question for soil hazard is 'is root anchorage restricted?'

Look at base of root system to see if it is restricted. Unrestricted root systems are typically bowl-like. They are deepest in the centre. Structural roots radiate out in all directions and get smaller and smaller as they reach the perimeter of the root ball.

Moderately restricted root systems extend for some depth into mineral soil but are flat bottomed. Roots at the base are bent or brushed off due to a mechanical barrier or water table.

Severely restricted root systems are superficial and plate-like. Trees attempt to build a platform.

Poor drainage or low strength organic soils decrease the strength of anchorage.

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