Factors are crucial for the way systems actually functions and therefore also an essential part of G-Codex.
Forest and city are both influenced, even build by biotic (living components) and abiotic factors (nonliving components). Together they make the living conditions in a forest or in a city. They define the habitats, the places where organisms live. Every habitat has it own community of organisms which interact with each other.
There are processes within the ecosystem which can deal with the biotic factors which destabilise the system. In fact they are feedback mechanisms. You can read more about them in Process.