Use and value renewable resources and services

The old proverb

Holmgren pairs the principle with the saying "Let nature take its course." He reads it as a warning against trying to master nature through heavy use of resources and high technology, which tends to be costly and to cause new harm.

The saying is not a call to do nothing. It means working with processes that run anyway, letting the season, the soil life and the plants carry as much of the work as they can, and putting human effort where it adds what nature cannot. A gardener who sows a green manure instead of buying fertiliser, or leaves fallen leaves under the trees instead of raking them away, is letting nature take its course in exactly this sense.

How it looks in nature

Ecosystems run almost entirely on services that organisms provide for each other. Flowers trade nectar and pollen for pollination. According to the assessment of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES, 2016), more than three quarters of the leading types of food crops worldwide depend at least in part on animal pollination, and so do close to nine in ten wild flowering plants. Mycorrhiza fungi bring water and phosphorus to roots and receive sugar in return. Rhizobia in root nodules fix nitrogen. Dung beetles bury dung, earthworms draw leaf litter into the soil, birds and bats hunt insects. A tree in summer evaporates water through its leaves and cools the air beneath its crown.

None of these services is free in the sense of costing nothing. Each partner gets something back, and each service lasts only as long as the relationships behind it stay intact. That is why the principle says value and not only use. A service nobody notices is easily destroyed, and pollinators sprayed away or soil life ploughed under then have to be replaced at a price: with hand pollination, bought fertiliser, irrigation and machines.

Where the principle works in the TerraWiki

• Nitrogen-fixing plants bring nitrogen from the air into the soil through their partnership with bacteria, a service that replaces bought fertiliser.
• Mycorrhiza and the soil food web are the unseen workforce of fertility; the principle asks us to spare them deep tillage and bare soil.
• Pioneer plants and nurse trees give shelter, shade and soil cover to the plants that follow, and ecological facilitation describes the science of such help between species.
• Biomass plants and the dynamic accumulator are grown as renewable resources: cut again and again, they regrow and feed the soil with their cuttings.
• In a silvopastoral system, grazing animals mow, manure and turn grass and leaves into food, work that would otherwise need machines and fuel.
• Rainwater harvesting and the roof water cistern catch a resource that renews with every rain, instead of drawing on groundwater that in many dry regions is pumped faster than it refills.
• Energy flow explains why sunlight captured by leaves is the renewable source on which all these services finally run.

At Sa Medada

Sa Medada is a slope in Jerzu, in Ogliastra on the east side of Sardinia. Its renewable income is the sun, the rain of the mild winters and the growth these two allow. The dry season from about May to September sets the limit: whatever is not held in the soil and in living plants by then is missing in summer.

Project Eden therefore begins with pioneer plants, ground cover and holding water, three services the land can largely provide for itself once they are started. An old olive grove covers part of the site, and macchia grows on the steeper slopes; both already shade the ground and drop leaves onto it. Swales are planned; none has been built yet.

Several nitrogen fixers are in the ground without inoculation, among them Tephrosia, the coral tree, Inga edulis, pacay, the Bambara groundnut, the fava bean and Leucaena. They depend on a service the soil itself has to provide, the right bacteria, and whether each species finds them is one of the open questions. Their prunings are meant to go back onto the soil as mulch; how much they contribute has not been measured. Leucaena counts as invasive in many tropical countries; for Terra Humana, fast-growing newcomers are nature's own strategy for renaturation, while species on the EU list of invasive alien species of Union concern are never used.

Along the journey

The fourth principle, Apply self-regulation and accept feedback, keeps renewable sources from being overused. The sixth, Produce no waste, takes the next step: once we value what renews, the leftovers of one use become the starting material of the next.