DNA and RNA provide a fingerprint of the community, and can detect the presence of specific species or groups. Food web complexity is a factor of both the number of species and the number of different kinds of species in the soil. Complexity can be determined, in part, from a food web diagram such as Figure 4, which represents the soil in an old-growth Douglas fir forest. Each box of the food web diagram represents a functional group of organisms that perform similar roles in the soil system. Transfers of energy are represented by the arrows on the diagram and occur when one organism eats another.
Complex ecosystems have more functional groups and more energy transfers than simple ecosystems.
Energy and nutrients will be cycled through fewer types of organisms. Land management practices can alter the number of functional groups or complexity in the soil. Intensively managed systems, such as cropland, have varied numbers of functional groups. Crop selections, tillage practices, residue management, pesticide use, and irrigation alter the habitat for soil organisms, and thus alter the structure and complexity of the food web. Researchers have yet to define how much and what kind of food web complexity in managed ecosystems is optimal for these soil processes.