Tree diversity makes its strongest mark belowground

Measuring a forest from the soil upwards

A study published on 31 August 2026 in Nature Ecology & Evolution shows why a forest’s diversity cannot be read from its canopy alone. Increasing tree species richness in a young experimental stand was associated with higher abundance and richness in many belowground groups. Responses aboveground were more limited. Huimin Yi and colleagues considered microorganisms alongside invertebrates, allowing them to follow changes across several levels of the food web. Read the original study.

The MyDiv experiment is in Bad Lauchstädt, Germany. Established in 2015 on land previously used for agriculture, it contains eighty plots planted with one, two or four deciduous tree species. The design separately accounts for trees predominantly associated with arbuscular mycorrhizal fungi, ectomycorrhizal fungi, or mixtures of both. This lets researchers distinguish the number of tree species from their main form of fungal partnership and test whether those factors interact.

Separate influences do not guarantee synergy

The team identified nearly one hundred thousand invertebrates and assigned them to feeding groups. They also assessed bacteria, soil fungi and fungi associated with leaves. Greater tree diversity supported richer belowground communities, from microorganisms and nematodes to some predators feeding on other invertebrates. The response was not identical for every group, and abundance and taxonomic richness are different measurements.

Mycorrhizal type also strongly structured belowground food webs. However, mixing trees associated with different mycorrhizal types did not produce a general benefit exceeding their additive effects. This challenges an easy assumption that any mixture must generate an exceptional additional response. In this experiment, tree diversity and mycorrhizal type largely behaved as distinct influences on the wider community.

The researchers linked parts of the pattern to leaf quality, canopy complexity and nutrient availability. These offer plausible routes through which trees affect other organisms. Statistical models can identify relationships consistent with those routes, but they do not directly test every proposed mechanism. Root growth and turnover, for example, remain useful subjects for further investigation.

A field perspective, with limits

For a forest observer, the study encourages attention to trees together with their litter and soil. The kinds of fallen leaves and the structure of a stand can be recorded alongside its tree species. Such notes cannot count underground fungi or forecast a flush of mushrooms. This research concerns community diversity and ecological relationships, rather than the quantity of edible fruiting bodies available to collect.

The setting also matters. Young deciduous plantings on fertile soil do not represent every forest. Conifers were deliberately excluded to avoid adding further differences in litter quality and soil conditions. An April 2026 review additionally stresses that relationships between mycorrhiza and tree diversity change with spatial scale. MyDiv therefore provides a specific experimental reason to include belowground organisms when studying forests. Applying its results to older stands, other soils or different climates requires additional evidence rather than a universal planting recipe.