Growing Trees and Mushrooms Together Could Merge Afforestation Efforts With Food Production

Plant-forward diets in rich countries could have an astounding "double dividend" climate impact thanks to their combination of direct emissions reductions and potential land-use changes for carbon sequestration, according to the findings of a new study. Now, a new study published in the journal Science of the Total Environment suggests combining afforestation with mushroom cultivation could displace some need for cattle ranching, while simultaneously regenerating biodiverse, minimally managed, mixed-species hardwood forests in the tropics. 

Specifically, researchers Paul W. Thomas and Luis-Bernardo Vazquez looked at the potential for cultivating native tree species that have been inoculated with Lactarius indigo (aka indigo milk cap), a mushroom that is highly prized, easy to identify, and already grows naturally across much of South, Central, and North America. What they found was that, theoretically at least, mushroom production could actually outcompete cattle ranching for nutritional value. Here’s how they describe the potential in the abstract: 

“... We show that a protein production of 7.31 kg per hectare should be possible, exceeding that of extensive pastoral beef production. In contrast to commercial agriculture, L. indigo cultivation may enhance biodiversity, contribute to conservational goals and create a net sink of greenhouse gases whilst at the same time producing a similar or higher level of protein per unit area than the most common agriculture use of deforested land.”

Thomas explained to Treehugger via a Zoom interview that the research came out of discussions that he and Vazquez had been having about mushroom cultivation as a potential strategy for rural income and food security projects in Mexico. Combining these goals with an emerging understanding of just how badly climate change will impact biological systems, it seemed like a potentially powerful strategy for balancing the competing demands of agriculture, biodiversity, conservation, and carbon sequestration.  

Thomas says because Lactarius indigo is an ectomycorrhizal fungi, meaning it forms a symbiotic relationship with the roots of certain trees, it should be possible to regrow large amounts of a forest while simultaneously producing valuable food.

“You see all these lofty goals on tree planting," said Thomas. "The UK’s Climate Change Committee says we should be planting 30,000 hectares a year, for example, but we are not even close. And the same is true of countries all around the world. Around 70% of the deforested Amazon rain forest is currently felled for pasture, so it’s clear that something needs to change.”

What would these proposed mushroom farms look like? He described a landscape that would look very similar to naturally occurring forests.

“In Costa Rica, for example, you have very little virgin rainforest left. What you have is secondary growth forest, which was once felled, but has been allowed to regenerate," said Thomas. "The kind of systems we’re proposing would look very much like that. The trees inoculated with milk caps would be combined with a mix of different native species for biodiversity, and there would be minimal forest management needed year-round. Once established, the main activity would then be sending in foragers to harvest the mushrooms when conditions were right for fruiting.” 

As for whether there were advantages purely in terms of tree growth, given the symbiotic relationship between fungi and trees, he was careful to offer a word of caution.

“Theoretically, in the lab, there are benefits in associating tree seedlings with mycorrhizal fungi. Out in the field though, that’s much harder to say," said Thomas. "After all, we’re not short of fungi out in the real world—as soon as you plant a tree, it’ll naturally start forming relationships with different fungi and bacteria. While it might be nice to believe that these inoculations give trees a boost too, in practice, the primary conservation benefits come from the fact that producing significant amount of protein while simultaneously replanting forests reduces the threat of deforestation.”  

While there’s a lot of intriguing promise in this paper, Thomas was also clear that much work remains to be done. Having looked at the theoretical potential in terms of food production, as well as the viability of identifying viable host species and inoculating them successfully, Thomas and Vazquez are now keen to turn their attention to the sociological and economic factors. For example, Thomas noted there will likely be tradeoffs between how land will be managed. More intensively managed land, for example, might produce more food, but with less conservation value. Similarly, it might be possible to grow really biodiverse, healthy forests but at the cost of making mushroom cultivation a less significant, ancillary benefit.