Scientists have examined the relationship between forest fungi and mature trees in greater detail than ever before.
Turns out the more fungal colonies they're connected to, the better the trees grow – an important discovery for forest management and climate change response.
Previous research has shown how fungal organisms can support trees at the seedling stage by passing over nutrients and water, and how older trees can support seedlings in the same way via this fungal network. Here, the team wanted to look specifically at the link between fungi and older trees.
Core samples taken from 350 Douglas firs in British Columbia showed that the wider a tree's network – connections to other trees enabled by fungi colonising their roots – the more growth the tree saw year on year. It's not certain that the wider network is causing the extra growth, but it's a strong correlation.
"We found that the more connected an adult tree is, the more it has significant growth advantages, which means the network could really influence large-scale important interactions in the forest, like carbon storage," says ecologist Joseph Birch from the University of Alberta in Canada.
The researchers explain that fungal networks act as a sort of highway for tree resources – and they can even transmit warnings from other trees about insect attacks and other dangers. When certain trees are struggling, and in poor health, other trees can help out.
Another finding from the study was that trees with connections to more varied fungi types also fared better in terms of growth. Apparently, the more diverse the underground support network, the better for these older trees.
Understanding this symbiotic relationship is going to be crucial in protecting forests for the future and keeping them in good health – not only are trees good at soaking up carbon, they also excel at protecting against soil erosion.
"Large trees make up the bulk of the forest, so they drive what the forest is doing," says Birch. "These networks may help them grow more steadily even as conditions become more stressful, and could even help buffer trees against death."
There's plenty more investigation to be done – this study only looked at one type of tree in one part of the world over 16 years, and these sorts of fungal networks are likely to vary from area to area and even year to year. Having more data is always helpful in understanding exactly what's going on in an ecosystem.
Future studies will also need to take a closer look at exactly what nutrients and resources are being passed from fungus to tree root and back again. It's possible that we might find a way of making trees more resistant to the rigours of climate change.
We can thank fungi for helping animal life on Earth get started in the very beginning, and now it seems these fascinating organisms are going to have a crucial role in conserving life on the planet as well.
"Knowing whether fungal networks are operating the same way in other tree species could factor into how we reforest areas after harvesting them, and it could inform how we want to plant trees to preserve these networks," says Birch.
The research has been published in the Journal of Ecology.