Stabilizing the Climate with “Permanent Agriculture”

Trees are one of our most powerful tools to pull carbon from the atmosphere and sequester it in the soil for long-term storage. This is why reforestation and protecting intact forests are such important parts of plans to address climate change. Conventional climate change science tells us that the planet’s capacity for reforestation is limited, however, by the need to preserve land for agriculture.

But movements like agroforestry and permaculture show us that farming and trees are not mutually exclusive. From tree crops to contour strips of nitrogen fixing trees between bands of annual crops, there is a wealth of techniques that can give us the best of both worlds. These techniques, should a global effort get behind their implementation on a large scale, could have a major impact on climate change. They would also have numerous other benefits to the planet and its people.

A century ago, writer-farmers like J. Russell Smith coined the term “permanent agriculture” to describe food forestry and other farming practices that combated a key issue of their day — erosion and degradation of farmland. From Smith and his compatriots we in permaculture have taken the name of our movement, though our movement has grown to encompass much more than food forestry. Today these visionary ideas are more essential than ever, to address an environmental crisis on a scale Smith and his contemporaries could not have imagined.

Potential Climate Impact

Trees are fundamentally more efficient than annual crops, with greater net primary productivity. They are larger, leaf out earlier, and start the growing season ready to grow in contrast to annual crops. There is a bigger carbon “pie” to be divided among wood, soil carbon, and food for people than annuals can provide. What can science tell us about the carbon sequestering capacity of permanent agriculture strategies like agroforestry, silvopasture, and food forestry?

Intuitively it makes sense that forest-like agriculture will sequester carbon somewhat like a “real” forest. Broadly speaking this appears to be the case. In their excellent 2004 review of the subject (“Carbon sequestration: An underexploited environmental benefit of agroforestry systems,” in Agroforestry Systems 61:281-295), P.K. Nair and Francesca Montagnini state that generally agroforestry systems sequester somewhat less carbon than forests, though still much more than most annual systems (many of which are net releasers of soil carbon to the atmosphere, and they cause emissions as a result of heavy fossil fuel use). I should note that most agroforestry systems integrate functional trees like nitrogen fixing legumes with annual crops, and proper food forestry with mostly perennial crops could come much closer to the amounts of carbon sequestered in “proper” forests.

The amounts sequestered vary hugely, depending on several variables:

  • Rainfall: humid climates sequester more than dry ones
  • Climate: temperate climates sequester more than tropical ones
  • Species: sequestration varies by species, with some standouts like mesquite
  • Management: layout and management practices have a huge impact
  • Design: polycultures sequester more carbon than monocultures in some studies

Allowing for these factors, Nair and Montagnini report estimates of the world carbon storage potential of agroforestry ranging from 9 to 228 tons of carbon/hectare under different circumstances — tremendous variation. They report an estimate of current sequestration by agroforestry at 1 million tons/year. Their document estimates the amount of land that could be converted to agroforestry practices as roughly 585 million to 1.2 billion hectares (the U.S. including Alaska is 770 million hectares). Even at a fairly conservative 25 ton/hectare average, that would sequester 14-20 billion tons — over its lifetime as much as 10% of the total 200 billion tons many experts estimate needs to be removed from the atmosphere even if we stop emissions tomorrow.

Sounds great — but that is a staggering amount of land. It works out to roughly 5-10% of the world’s land (excluding Antarctica), or a whopping 40-80% of currently used arable land.

Permanent agriculture doesn’t just sequester carbon. It is also a fantastic way to restore degraded land to productivity. Much of the carbon we are pulling from the air becomes organic matter, the foundation of productive agricultural soils. The Global Assessment of Human-Induced Soil Degradation (concluded in 1990) found that vast amounts of the planetary surface have been degraded by human activity, through erosion of sloping land, desertification, salinization, and nutrient depletion.

Perennial farming systems are particularly suited to stabilizing slopes and preventing erosion on hillside farms. Roughly 45% of the world’s farmland is classed as sloping at an 8% angle or higher. Regeneration of this quantity of farmland with permanent agriculture would sequester 16.8 billion tons of carbon (at 25t/ha).

About 135 million hectares of farmland have an unbelievable 30% slope or greater. I have seen miles of corn growing on mountainsides far steeper than this in Guatemala. These lands are severely eroding and completely unsuitable for annual crops without extensive terracing, living contour hedgerows, or (preferably) replacement with tree crops. If a targeted international project began just focusing on these most vulnerable agricultural areas, 9% of total world farmland, we could (at 25 t/ha, towards the low end of agroforestry’s potential) still sequester 3.3 billion tons of carbon — equal to a third of all human-caused carbon emissions released annually.

Don Victoriano and Doña Corina of the community of El Matasano in
Chiquimula, Guatemala using an A-frame level to mark contours for living
terraces. In the background are steep mountainsides covered in cornfields.
Photo courtesy Ripple of Hope.

Of course perennial agriculture is only one element to incorporate in a larger effort to slow global warming. Reducing fossil fuel use, converting to clean energy sources, and reevaluating everything from transportation to economic policy are all necessary. But the carbon-sequestering capacity of food forestry and allied systems could and should be a major component of humanity’s efforts to prevent runaway climate change.

So what exactly are the practices that have such great potential to stabilize the climate? The elements of perennial farming systems include perennial crop systems, perennial-annual integration strategies like agroforestry, and livestock-perennial combinations.

Perennial Farming Systems

This suite of practices, which I am collectively calling perennial farming systems, represents some of the best of today’s “permanent agriculture” practices. These strategies improve the productive capacity of the soil over time, leading us to call them “regenerative agriculture.” While permaculture did not invent these practices, we have worked hard to integrate, refine, and adopt them around the world.

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Perennial Crops

The first major category of carbon-sequestering permanent agriculture is perennial crop systems. These crops offer multiple benefits: once established they are no-till, require minimal fossil fuel inputs, and offer long-lived productivity. Systems using these crops include traditional orchards, multi-layer food forests and forest gardens, and herbaceous perennial farming from asparagus and globe artichokes to perennial grain polycultures. While some perennial fruit and nut crops are well known, perennial vegetables are still a fairly new concept for much of the world, and perennial staple crops providing our daily carbohydrates and protein are sadly a rarity. I have been researching the many fascinating perennial staple crops of the world — you can read my article on this here. Though getting people to adopt new foods can be challenging, these crops allow us to eat directly from carbon-sequestering plants.

Mesquite trees are a fascinating example. These nitrogen-fixing trees are highly drought-resistant, with roots a remarkable 450 feet deep. Mesquite pods are edible and nutritionally comparable to wheat. However, mesquite trees can produce as much or more food per acre than wheat or other annual staple crops. Mesquite species are native to arid regions of Africa, Asia, and the Americas, and are under development as a new perennial staple crop. They can sequester up to eight tons of carbon per hectare annually on good soils as a monoculture. Though they are most productive with decent rainfall, mesquites can crop on as little as 4” of rainfall annually! Check out Desert Harvesters’ brand new Eat Mesquite!, a fantastic cookbook with lots of information about this important but neglected crop.

Other Perennial Crops

Perennials provide much more than food. Most material human needs can be met by some form of perennial plant. Fuels are a great example, from coppiced nitrogen fixing firewood to castor oil biodiesel and milkweed gasoline. Timber and construction materials are a major perennial product, with bamboos as a standout plant family providing long-term harvests in perennial systems. Other products include plastics, fibers, herbicides, medicines, mushroom substrates, crafts, and on and on.

Perennial Crop Polycultures

Of course we are not advocating massive monocultures of any of these perennial crops. Vast corporate oil palm monocultures are a perfect example of what can go wrong when promising ideas like perennial crops and biofuels are filtered through the corporate mindset. Rainforests on carbon-banking peat soils are being cleared for oil palm plantations on a massive scale, in the name of “green” biofuels, at a net loss of carbon to the atmosphere. That’s not the win-win we are looking for.