The world hungers for more food while wildlife yearns for untouched habitats. So goes the conflict between our seemingly insatiable need for agricultural land, razing forests to make way for cattle and crops.

But an unlikely food source could go some way to ameliorating the loss of forested lands to agriculture. A new study suggests that edible fungi may represent a mighty opportunity to produce protein-rich food stuffs and lock away extra carbon in soils – all while expanding tree plantations.

"We've got very ambitious tree-planting targets in Scotland and across the UK more generally," explains Alastair Jump, a plant ecologist at the University of Stirling in the UK, who co-authored the new study with fungi expert Paul Thomas.

"Those trees have got to go somewhere and that can be at the expense of agricultural land," says Jump. "This [approach] gives us an avenue to get trees and an edible crop into the same space."

While a diet of only mushrooms isn't sustainable or appetizing, edible fungi are high in fiber, contain essential fatty acids, and could substitute other sources of protein, such as beef, pork, and poultry, in people's diets.

On a global scale, and based on the past decade of tree-planting efforts, the researchers estimate that growing edible fungi on existing forestry lands could bump up food production without clearing more forests, while feeding millions of people annually.

That is, of course, if emerging techniques for co-culturing fungi and seedlings can be scaled up.

The pair's big idea is that edible mushrooms, such as the easily identifiable blue milk cap (Lactarius indigo), could be cultivated amongst trees that are either planted in an orchard-like system, or to restore forests in line with conservation goals.

The fruiting bodies of mushrooms like L. indigo could be collected and grown in the lab, with the spores then used to inoculate young tree saplings before they are planted.

The fungi naturally form an intimate relationship with trees, entwining themselves around spindly plant roots, where they exchange minerals and nutrients in return for carbon. As the trees develop, the underground fungal network also grows, sprouting mushrooms as it goes.

If cultivated on a large enough scale, this could "lead to more food production, with all the benefits forests bring and without the environmental burdens of intensive farming such as fertilizer, water use or the growing of additional feed," Thomas, who holds a stake in a mushroom cultivation company, explained in a recent article for The Conversation.

It's a well-known and escalating problem that many aspects of agriculture release greenhouse gasses; from the plowing and tilling of soils – which, if left undisturbed, can hold onto the carbon that plants worked hard to absorb and draw down into their roots – to the manufacturing of fertilizers, which also release nitrous oxide when applied to crops.

On the other hand, mycorrhizal fungi can store carbon in soils over long periods in a vast web of filaments called hyphae, so long as those soils aren't overturned.

The upper estimates of the analysis, which combines data collected from forestry plots along with remote-sensing data of forest extent, suggest that adding mushrooms to boreal forests in northern environments is an opportunity that represents 12.8 metric tons of stored carbon each year.

Only half as much carbon could potentially be sequestered if the approach were to be adopted in temperate forests.

Bear in mind that boosting the carbon content of soils, at scale, is an imprecise science that comes with a lot of hype and which experts say might be overly optimistic. It relies on good measurements of soil carbon levels – and of course, for forests to be protected in perpetuity.

Experts also warn that reforestation efforts favoring single species over restoring native forests create monocultures that fail to fully recover the biodiversity of intact forests.

The 'wood-wide web' of fungal networks said to connect whole forests of trees has also been called into question recently, with a trio of researchers claiming estimates of its expanse may have been exaggerated.

While growing alternative protein sources certainly could help reduce our meat consumption, it has been suggested that changing our food production systems, tackling food inequity, and eating locally sourced foods are other important ways of cutting greenhouse gas emissions and ensuring food supplies into the future.

The study has been published in PNAS.