The richest soils in the world are in cool and cold temperate forests. It was once said that a squirrel could travel from Washington state to Maine without ever touching the ground. In the northern part of the United States there still can be found rare pockets of top soil that go to depths of six feet.
It is not widely known that the temperate climate has a deficiency of nitrogen fixing plants and trees when compared to the dry lands or the tropical climate regions. It is not that legumes and dynamic accumulators do not exist in this region but rather that the temperate climate is set on the earth in such a way that it’s cyclical seasonal events create for a very unique set of circumstances that produce a high quality life rich soil quickly (quickly in nature’s terms). This climate is granted the gift of having two start and stop periods (spring and autumn), where a quick flourish of growth blankets the ground and then dies back every winter and summer providing layer upon layer of organic matter. Same can be said with the deciduous trees in the region in which the trees grow leaves, drop them, and then those leaves decay creating a friable hummus rich organic material on the soil surface.
Permaculture is based in optimism, but sometimes we need a base point on where to begin. Currently if you are farming in the United States then you are allowed four tonnes per acre of top soil loss per year. If we put on a budget lens this clearly becomes insanity. Nature is not equipped to produce soil anywhere close to the rate of current soil loss. Conventional practices, permanent pasture, and current agricultural methods will lead to desertification and famine. A replacement to permaculture models will lead to perpetual soil gain, plant and animal diversity, and an economic system that is not based on finite resources.