The Seed Cycle

Where the cycle breaks in ordinary land use

Seed is bought, not grown. In much of today's farming the cycle no longer turns on the farm at all. Many crops are grown from F1 hybrids, whose seed does not come true, so new seed is bought every year. The adaptation that used to build up over generations in a field stays with the breeder. The market for this seed is concentrated: according to estimates by Philip Howard, four companies controlled more than 60 percent of global sales of proprietary seed after the mergers of 2016 to 2018.

Diversity is lost. As local varieties gave way to uniform ones, much of the diversity within crops disappeared. FAO has estimated that some three quarters of crop genetic diversity was lost during the twentieth century; that figure is a rough estimate, not a measurement. A large review by Khoury and colleagues found marked losses in landraces on farms, in modern varieties and in the wild relatives of crops, as well as cases where diversity held or recovered. Every lost variety is an answer to a local problem that has to be found again.

Flowers and carriers disappear. Monocultures flower briefly or not at all, and herbicides remove the wild flowers in between, so pollinators find little to live on. Klein and colleagues point out that intensive farming puts at risk the wild bee communities that help keep pollination stable. Hedges, lone trees and field margins are cleared, and with them the perches where birds rest and drop seeds.

The seed bank is emptied. Ploughing, herbicides and bare soil wear down the store of wild seeds in the ground, and erosion washes away the topsoil in which it lies. Seedlings that do come up on bare, hot ground or under heavy grazing rarely survive. The result is land that has lost the ability to sow itself and has to be replanted by hand.

Techniques that let the land sow again

All of them return the cycle to the land: more flowers, more carriers, covered soil where seeds can land, and shelter for the young plants. The cycle graphic above shows where each technique works.

Mother plants. Old trees are the seed source of a landscape. Millennial olive trees and other monumental trees carry the genes of populations that have survived centuries of drought and heat. The maquis is the reservoir of native shrubs from which a slope can renew itself, and rare species such as the service tree depend on every mother tree that remains.

Flowers and pollinators. Polyculture and the plant guild keep something in flower through most of the year. A herb spiral gathers flowering herbs in a small space, and a food forest adds flowering trees and shrubs at several heights.

Ripening seed. A living mulch of subterranean clover sows itself: it pushes its seed heads into the soil in spring, dies back in summer and comes up again after the autumn rain. A cover crop between trees can be allowed to flower and set seed for the same reason. Saving the seed of crops and vegetables closes the cycle by hand; it deserves its own page.

Dispersal. The holm oak and the cork oak depend on jays to carry their heavy acorns into new ground. Agroforestry brings back trees and hedges as perches. A meta-analysis by Guidetti and colleagues found that even artificial perches increase the number and variety of seeds that birds bring into degraded land, and the number of seedlings beneath them.

Seed bank in the soil. Ecological succession starts from what lies in the ground. Indicator plants show what the seed bank and the soil still hold, and a biological soil crust binds open dry ground so that the first seeds can germinate.

Germination. Small earthworks catch seeds together with water. The zaï pit collects wind-blown soil, leaves and seeds; in Burkina Faso, trees sprouting from seeds in the manure of such pits grew into a forest. The half-moon and the microcatchment give a seed a moist place to start, and mulch keeps it from drying out.

Young plants. Nurse trees shade seedlings through their first summers, and pioneer plants prepare the ground for those that follow. Ecological facilitation explains why young plants often survive better near others than alone, and regreening shows how dry land returns once seedlings are protected.

Adaptation. Climate-adapted trees and assisted migration help the cycle keep pace with a warming climate, for example by sourcing seed from the hottest and driest edge of a species' range. Ecological restoration combines all of this into a landscape that renews itself.

How it looks at Sa Medada

Sa Medada is a slope in Jerzu, in the Ogliastra on the east side of Sardinia, with mild winters and a dry season from about May to September. For seed, that dry season is the bottleneck: a seedling that germinates after the autumn rain has a few months to send its roots deep enough before the summer. An old olive grove covers part of the land, and maquis grows on the steeper slopes. Those shrubs are the native seed store of the place, and the moister channels along the edges, which the LiDAR wetness map shows, are likely to give seedlings the best start.

Project Eden begins with pioneer plants, ground cover and water retention, which in terms of the seed cycle means preparing the ground on which seeds can land, germinate and survive. Among the plants in the ground are annual seed crops such as fava bean and Bambara groundnut, whose seed can be harvested and sown again, and the service tree, a rare species, planted in 2024 as the first tree, on the very hot southern flank. Others, such as black and white sapote, feijoa and Surinam cherry, still grow partly in pots.

Whether and how Project Eden will save its own seed, and which plants on the slope will begin to sow themselves, is still open. The seed cycle is the slowest of the cycles to close, because it advances only one plant generation at a time.