The Role of Trees and Perennial Plants in creating Climate-Friendly Food Systems
As we confront the impacts of climate change and assess the role of food systems in either exacerbating or alleviating climate catastrophe, it becomes apparent that our industrialized model of food production is no longer viable. The conventional industrial agricultural model is extractive and destructive, often using a disproportionate amount of energy (resources, labor, fuel, and capital) to produce food while externalizing costs to people and the planet. Thankfully, there are lessons to be learned and valuable insights to be gained from the ways that indigenous peoples cultivated food in pre-colonial and pre-industrial times.
While our earliest ancestors depended on the cycles and systems of nature for sustenance, such perennial food systems continue to be central to indigenous foodways around the world today. In her book titled Edible Perennial Gardening, Anni Kelsey points out that “variations on the forest gardening theme occur in traditional cultures around the globe. However, ‘development’ and the importation of European/western agricultural practices have largely displaced the old ways. With its roots deep in ancient practices, forest gardening is being rediscovered as a remarkably useful and relevant approach to growing food.” Learning to produce food from perennials is a matter of critical importance if we are to continue to feed ourselves in a rapidly changing climate.
In normal gardening lingo, ‘perennial’ is typically used to describe a low-growing herbaceous or evergreen non-woody plant that doesn’t require replanting year after year. However, it’s important to take a wider perspective to include trees and shrubs with edible fruits, roots, shoots, and leaves; aquatic perennial plants; vines; bulbs; roots; tubers; and even so-called “replant perennials” like potatoes. Perennial grains should also be considered, as the cultivation of land to grow annual grains – on which a large proportion of the human population depends – is one of the factors that make agriculture such a large emitter of greenhouse gasses. Thus perennial grain crops must be an essential part of our future food strategy.
Hackberry tree loaded with berries in a drought year
Unfortunately, the way agriculture has developed into an almost entirely short-lived and highly mechanized method of growing monocultures of vegetables and grains, means that perennials have been somewhat left behind. Our myopic focus on yield, along with our perceived need for mechanical tillage, mechanical harvesting, and toxic agricultural chemicals to keep our systems weed-free and productive have led us down this path. It’s true that mechanical and chemical weeding and harvesting aren’t easy with perennials; nor do they boast rapid single-season yields when compared to their annual counterparts. Although, over its lifetime the perennial will usually yield many times the yield of an annual.
Moreover, a comparison of yields is meaningless unless it takes a wider view of the system as a whole. This constant push for the highest annual yield causes us to lose sight of the many hidden yields and services provided by the farm ecosystem, which go unnoticed and undervalued in our conventional agricultural systems. These ecosystem services – including nutrient cycling, soil building, carbon sequestration, increased biodiversity, erosion control, water conservation, and provision of beneficial habitat, shade, and windbreak – must be considered in our true cost accounting of the overall value of a system.
Annual soil tillage is one of the worst offenders in agriculture in terms of carbon emissions, so it’s important to note that most perennials (excluding root crops, tubers, and replant perennials) avoid the need for tillage. This lack of disturbance helps maintain the integrity of the soil ecosystem, both in terms of the soil structure – critical for holding water and preventing erosion – and the rich microbial life in the soil, including the network of beneficial mycorrhizal fungi. This network helps feed plants in a symbiotic relationship where the fungal hyphae (the fungal equivalent of roots) supply plants with hard-to-get nutrients in return for some sugars from the plant. Mycorrhizal fungi also protect plants from pests and disease, allowing them to communicate and move nutrients long distances through the soil, and they are critical in the sequestration of carbon in soils. Maintaining the integrity of the soil microbiome improves the overall health and fertility of the system, making it more productive and less reliant on resource-intensive inputs like pesticides, herbicides, and fertilizers.
Three different kinds of pollinators jostling for position on this allium flower
A mass of fungal hyphae called mycelium growing on biochar
Climate change has worsened the frequency, intensity, and impacts of extreme weather events, creating another opportunity for perennials to shine. Once established, perennials are able to cope with drought much more effectively than their annual counterparts, only requiring watering under exceptional circumstances of prolonged periods without rain. When we do get rain in this era of climate upheaval, it tends to arrive in more intense bouts, and perennial systems with their deep root systems and robust soil organic matter create a living sponge that is better equipped to absorb water without washing away precious topsoil or drowning the plants.
Perennial food systems also offer genetic advantages that make them more resilient in the face of climate change. Developed varieties of most annual plants have had their naturally-evolved disease and pest defenses bred out of them, whereas many perennials retain some of their natural defenses, adaptations, and genetic diversity. It’s worth noting that even within the category of perennials, some crops, such as apples, pears, peaches, and blueberries, have undergone extensive selection and breeding in the interest of domestication and at the expense of resilience, so opting for perennials that have undergone less selection and breeding like persimmon, papaw, saskatoon, native grapes, and hardy kiwis will reap greater rewards.
Interplanting perennial plants into polycultures with varying heights, root depths, structures, and leafing and fruiting times offers a number of additional ecological benefits. Keeping the soil covered with plant growth of various heights and widths protects soil structure and prevents erosion of precious topsoil by shielding it from drying sun, heavy wind, and pelting rain or hail. Keeping various depths and varieties of living roots in the soil year-round provides diverse sources of nourishment and habitat for beneficial soil microorganisms, which, in turn, provide nutrients and natural pest control to the green bodies of the plants. Diverse polycultures also attract diverse beneficial insects, providing food and habitat for insects that pollinate crops and/or prey upon “pest” species, eliminating the need for insecticides.
Additionally, plants in diverse polycultures offer different system functions which contribute to greater health of the system as a whole, benefiting all soil life and ultimately everything that grows in it. For example, in a well-designed agroecosystem, there may be pollinator-friendly plants, plants that attract beneficial insects, plants that are nitrogen-fixers, and plants that are mineral accumulators (those with deep roots that are very efficient at extracting minerals from deep in the soil, accumulating them in the roots and green body of the plant) so that those nutrients can be shared with shallow-rooted plants in the vicinity. Designing productive food systems with these factors in mind allows for a closed-loop, ecologically harmonious system.
In short, perennial food crops contribute to climate change adaptation and mitigation and offer resilience by providing ways to prevent erosion, improve soil structure, increase ecosystem nutrient retention, facilitate carbon sequestration, improve water infiltration, and reduce the need for resource-intensive inputs. Overall, these regenerative systems help ensure food and water security over the long term. Incorporating perennial crops in polycultures (mixtures deliberately grown together in ways that minimize competition and make use of beneficial interactions between plants) allows for an expansion of these benefits and can give birth to productive closed-loop ecosystems in our farms and gardens, even when we still want annual crops in the mix. To learn more, visit The Land Institute at landinstitute.org.