Apply self-regulation and accept feedback

The old proverb

Holmgren gives the principle the saying "The sins of the fathers are visited on the children unto the seventh generation." Its subject is time. Negative feedback often arrives late, sometimes long after the people who caused it are gone: soil lost to erosion, a spring that runs dry, a hillside stripped of its trees. The saying echoes the Bible, where the book of Exodus speaks of the third and fourth generation; the version Holmgren uses stretches the span to the seventh and makes the delay longer still.

The same delay works the other way. Whoever plants trees, builds humus or holds water in a slope leaves something that keeps working for generations. The principle asks us to shorten the path between cause and signal wherever we can, so that a mistake shows itself while it can still be put right.

How it looks in nature

Nature is full of balancing loops. Legumes are a good example. They feed the bacteria in their root nodules with sugar, and in return the bacteria fix nitrogen from the air. When the soil already holds plenty of nitrate, many legumes form fewer nodules and fix less. It is as if they stopped paying for what they can take up more cheaply, though how exactly nitrate applies this brake is still being studied. Nitrogen-fixing plants thus match their own contribution to the state of the soil.

Leaves close their pores in drought and lose less water. Predators multiply when prey is plentiful, eat it down and then decline themselves, so that neither population runs away. In ecological succession, pioneer plants shade and feed the soil until the conditions they have created favour other species, which slowly take their place.

Reinforcing loops show what happens when the brakes fail. In dry country, plants help rain soak in and shade the ground, and this helps more plants to grow. Take them away, and the bare soil seals, sheds the water and stays bare. Max Rietkerk and colleagues (2004) reviewed studies from drylands and other ecosystems showing how such loops can tip a landscape from vegetated to barren in a sudden shift, and why it is so hard to tip it back. Feedback in nature is therefore more than a regulator. It is also the reason why damage, once it passes a threshold, can feed on itself.

Where the principle works in the TerraWiki

• Indicator plants are the land's own report: what grows of its own accord speaks about water, compaction and nutrients long before a laboratory does.
• The spade test and the texture-by-feel test turn feedback into a habit that costs only a few minutes.
• Soil analysis adds measured values where observation is not enough, and repeated over the years it shows the direction of change.
• Soil erosion and soil compaction are the warnings worth heeding early, while a rill is still a rill.
• In a silvopastoral system, animals move on before they overgraze; the state of the pasture sets the timing, not the calendar.
• Polyculture and the plant guild build balancing loops into the planting itself, because pests that race through a single crop meet barriers and natural enemies in a mixed one.
• Syntropic agriculture steers by pruning: the gardener watches how each layer responds and cuts accordingly.

Cycle thinking looks at the same principle from another side, because every leak in a loop is a piece of feedback.

At Sa Medada

Sa Medada is a slope in Jerzu, in Ogliastra on the east side of Sardinia, with mild winters and a dry season from about May to September. Much of the early work there is a way of asking the land questions and listening to the answers.

The LiDAR wetness map is one such answer. It shows a comparatively dry main area with moister channels along the edges, and so it tells Project Eden where water already gathers before anything is built. Swales are planned; none has been built yet. The first tree, a service tree, went into the ground in 2024 on a very hot south-facing slope, a test of what the place can carry. Bananas, mango, avocado, cherimoya, papaya, moringa and citrus are being tried in the microclimate, and how each of them fares is feedback of its own.

Several nitrogen fixers grow there without inoculation with root-nodule bacteria. Whether each species finds its partners in the soil without help is one of the open questions. A laboratory analysis of the soil does not exist yet, and so we make no claims about its nutrients. Until it does, the plants themselves are the first report.

Along the journey

This principle follows Obtain a yield. A yield is the reward that keeps people at their work; self-regulation keeps that work from taking more than the land can give. The next principle, Use and value renewable resources and services, asks which of nature's own services can take over tasks we would otherwise do with fuel and bought inputs.