For this destructive process to be successful, all that is needed are a few simple ingredients, wood, moisture, oxygen, decaying organisms, nutrients from the soil and a temperature above 10 C, and away you go.
At depths over 200mm below ground level, the conditions for any serious form of rot and decay are greatly reduced if nothing else because the temperature is generally well below 10c and oxygen and nutrient supply is restricted.
So this leaves the ground line section of the pole in conditions ideal for rot and decay, combine this with the fact that this is also mechanically the most highly loaded section of the pole and it’s hardly surprising that this is the common point of failure for timber poles.
So why do we need to worry about this? Wooden poles have traditionally lasted a reasonable period of time.
Traditionally wood has been treated with preservatives to prevent decay giving many years or decades of trouble-free service in a wide range of soil and timber types. Environmental pressures have resulted in changes to legislation affecting wood preservatives.