For generations, foresters have observed a curious phenomenon: certain trees grow better when planted alongside different species. Now, research from Zhou and colleagues has revealed the hidden mechanics behind this “nursing effect”. They studied how different combinations of trees affected the growth of Sitka spruce, Britain’s most important timber tree. They found that pines help foster beneficial soil fungi that can aid the young spruce trees.
The effect was large. Sitka spruce seedlings grew up to 60% more when planted in soil previously inhabited by Scots pine. The increased growth was correlated with a doubling in root colonisation by beneficial ectomycorrhizal fungi – from roughly 20% in spruce-only soil to over 40% in pine-conditioned soil. These fungi helped the saplings by helping them access nutrients, particularly by transforming phosphorus into forms the young trees.
The researchers devised a two-part experiment at Cannock Chase Forest in the UK to peek into the hidden life of forest soils. First, they carefully tended different tree combinations – spruce growing alone, pine growing alone, birch alone, or all three mingling together – for 34 weeks. Next, Zhou and colleagues planted spruce seedlings in these “conditioned” soils. They then watched the saplings grow for 24 weeks, measuring everything from root patterns to fungal connections.
The results won’t surprise foresters. It’s been known for a long while that diverse woodlands often flourish where single-species plantations struggle. The value of this research is that it explains why. There’s more to a forest than a lot of trees. They’re communities where species interact with each other in many different ways. With a theoretical basis for how these species help each other, there’s now a basis to work out how mixes of species can help each other.
Zhou, Y., Tao, T., Cox, F., & Johnson, D. (2024). Plant–soil feedback drives the ‘nursing effect’ on Sitka spruce. Journal of Applied Ecology. https://doi.org/10.1111/1365-2664.14848 (FREE)
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