The vital key to a working forest

Without decomposition the dead material in a forest would physically swamp the field and ground-layer vegetation, prevent new seedlings establishing and, most importantly, lock up nutrients to such a degree that woodland processes would grind to a halt. Decomposition is the breakdown by physical (abiotic) and biological means of organic material in and above the soil. The organic substances involved include plant material ranging from large woody trunks to leaves and shed parts, dead animals and their excrement. The process of converting the organic matter into the final humus is called humification. Along the way, as complex organic components are broken down, the nutrients are mineralized (transformed from organically bound nutrients to simple gases such as ammonia and carbon dioxide or soluble (ionic) forms) and released into the soil water where they can be absorbed by decomposers and green plants. As described in Chapter 1, in any ecosystem nutrients are recycled usually with very little input from outside, so any major bottle-neck in the cycle will affect all future activity, including plant growth.

The major gaseous product of decomposition is CO2 so decomposition is crucial in influencing the amount of carbon locked up in forests, a matter of increasing importance when looking at the implications of climate change scenarios and the large amount of carbon currently stored in the soil (see Chapter 11).