Marco Banks wrote:
The OP mentions that forests do not fertilize, yet they are green and lush and fertile. Yes and no. In an old-growth forest, the trees may live 500 to 1500 years old. Think about that ---- a beech tree or a redwood that lives for over 1000 years. And in all that time, how many trees will replace it? One. But there are hundreds of plants that struggle and die in that same forest. They never really thrive due to a lack of sunlight and fertility.
One mature tree eventually dies and one tree takes its place in the mature forest. Hundreds of millions of seeds will come off that tree during its 1000 year lifespan, yet only one will ultimately replace it. Millions of those seeds will sprout and die. Thousands of those seeds will grow for a while before eventually dying. Only one seed (on average) will mature to the size of the massive old tree it is replacing.
So how much fertility is necessary for that kind of system? Ultimately, the mother tree most likely supplies the nutrition to the baby trees surrounding her, and ultimately one of those baby trees will replace her. She will rot into the soil (perhaps thousands of tons of biomass slowly decomposing both above and below the soil). That is all the fertility the replacement tree will need for the rest of its life.