why is the soil in the temperate forest rich in nutrients?

On the forest floor of temperate rainforests the soil is dark and damp. This soil is richer than the soil of tropical rainforests partly because the trees in tropical rainforests spread their roots into large mats that suck all of the nutrients out of the soil. While temperate rainforests, because they are less biodiverse, have not developed plants that do that. "Nurse" logs are trees that have fallen and as they decompose they provide nutrients for the plants nearby.