Which energy sources would have the least ecological impact when used in the production of electrcity

Each autumn the forest floor is covered by leaves that have fallen from trees which type of organisms is most effective in decomposing the leaf tissue allowing the nutrients and minerals to be recycled in the environment?

We're always up for a good laugh, but, seriously, refrain from posting silly or answers. keep the quality of high by following the rules and posting thoughtful answers.

Love, which can’t be observed or measured directly, is an example of psychological construct