Trees with edible leaves can boost human nutrition: New book, free download

Trees are good for many things, and their widespread planting is promoted as a solution to challenges ranging from climate change to biodiversity loss, desertification of cropland and rangeland, to declining freshwater resources.

One less-appreciated benefit of growing trees is for their leaves for human nutrition, but a new book, Trees with Edible Leaves: A Global Manual, details more than 100 species whose leaves are highly nutritious and can be grown in many regions of the world, not just in the tropics.

Mongabay contacted the author of this new resource, which is available as a free download. Eric Toensmeier is the author of several books about sustainable agriculture and agroforestry, including The Carbon Farming Solution, Perennial Vegetables, Paradise Lot and Edible Forest Gardens. The common theme of these is how they center perennial plants as a solution that society can harness toward a more sustainable future. Reached via email, his responses have been edited for clarity.

Mongabay: Readers might be surprised to know that there are scores of trees with edible leaves, and that these can be quite nutritious. Are they familiar species, or unusual ones?

Eric Toensmeier: Hundreds of species of trees have edible leaves, with over one hundred grown for that purpose. Mongabay readers may be familiar with temperate species like mulberry and linden, plus commercially available species like moringa and nopal cactus, or iconic trees like baobab and ceiba.

As a group, trees with edible leaves have the highest concentrations of the nutrients that billions of people are missing in their diets, in both the Global North and South. A disproportionate number of the world's most nutritious vegetables are actually trees with edible leaves. These outstanding species include chaya, Siberian ginseng, cassava, noni, moringa, mulberry, and Chinese toon. We should note that these species are usually pruned back to 1-2 meters [3-6 feet] high each year for ease of harvest and to ensure a long season of tender leaves.

Mongabay: Beside the nutritional benefits, why eat tree leaves?

Eric Toensmeier: Some trees with edible leaves are delicious, with unique flavors like chicken soup or root beer. They are much easier to grow than annual vegetables, being very simple to maintain once established. They sequester carbon and make food production more resilient in the face of climate change. And they are well-suited to agroforestry systems, which represent the high bar of ecosystem functionality for food production. The shade tolerance of many species makes them perfect to grow under other trees in multi-layered agroforestry systems.

Mongabay: Can you say more about the species that grow in temperate zones?

Eric Toensmeier: We profiled 102 species in the publication, all of which are cultivated for their edible leaves, and 19 are temperate. I’ve grown species including mulberry, linden, edible-leaf goji, and Chinese toon for over a decade in Massachusetts, where winters are often very cold.

South Korea and temperate China are very active in bringing new temperate tree leaf vegetable species into cultivation. Over 30 species are suited to tropical and subtropical drylands, and 49 to the humid tropics (the total is over 102, because some species grow in multiple climates).

Mongabay: Can such trees also provide food for livestock (i.e. "fodder"), and for wildlife?

Eric Toensmeier: That's a good question, as it happens, I’m also working on a book about tree leaves for livestock, and many of the same species (like mulberry) and techniques (like pollarding) are used.

Tree fodder for livestock brings several important benefits – increased carbon sequestration in the pasture, reduced emissions of enteric methane from the animals that consume many (but not all) species of tree fodder, and better availability of foliage during long droughts, or during the dry season.

I imagine that these species offer benefits for wildlife as well, but because they are heavily pruned they tend not to flower or set seed, which limits their usefulness to pollinators and seed- and fruit-eating organisms like birds.

Mongabay: As a publisher of Creative Commons/freely available news and information about the environment, Mongabay appreciates that the book is available as a free download. Is there a goal of making the information as widely available as possible?

Eric Toensmeier: Because we were fortunate to have funding from the Trees for Climate Health initiative of Jonas Philanthropies, we are able to offer the publication as a free download. As a result, it was downloaded over 16,000 times in the first month.

We are at work on the Spanish translation and are seeking funds for translation to other languages as well.

Download a free copy of the book from Perennial Agriculture Institute's website, here.

View Mongabay's ongoing series about agroforestry here.

Banner image: Moringa stenopetala is a tree originally domesticated by Ethiopian and Kenyan farmers for its highly nutritious leaves. Image via Wikimedia Commons.

Related audio from Mongabay's podcast: Agroforestry is an ancient climate change solution featuring trees which also boosts biodiversity and is now being adopted around the world: a discussion with three guests, listen here:

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