The significance of retention trees for survival of ectomycorrhizal fungi in clear-cut Scots pine forests, Sterkenburg et al. 2019

Industrialized forestry simplifies forest structure and harms biodiversity. To mitigate this harm, retention forestry has been adopted in places such as Sweden, where this study was conducted. “Retention forestry” avoids clearcutting and instead preserves some 5-30 percent of trees to benefit populations of birds, lichens, fungi and other types of organisms.

The authors focused on the effects of retention on ectomycorrhizal (ECM) fungi (also commonly abbreviated as “EM” fungi), an ecologically important group of species.

ECM fungi represent a large part of the biodiversity in boreal forests. They depend on carbohydrates from their host trees and are vital for forest production, as uptake of nutrients and water by the trees is mediated by the soil ECM symbiosis. ECM fungal mycelium forms a basis for soil food webs. The largely cryptic life of ECM fungi has hampered understanding of their biology and their importance for ecosystem processes, impeding adaptation of forestry to sustain ECM fungal diversity [Sterkenburg 2019: 2].

Aiming to quantify the decline in ECM fungi species abundance and richness in relation to the proportion of trees logged, the authors established an experiment with two levels of trees retained (30% and 60%), which was then compared to unlogged forest (100% retained) and clear-cut forest (0% retained). They found that ECM fungal diversity and relative abundance is preserved in proportion to the amount of retained trees.        

“In clear-cuts, ECM fungal relative abundance had decreased by 95%, while ECM fungal species richness had declined by 75%, compared to unlogged plots” [Sterkenburg 2019: 1]. The latter result meant that the less common species of ECM fungi were lost, while the more dominant ones survived. The authors noted that even at the Swedish Forestry Council’s sustainability threshold of 5% tree retention (i.e., 95% logged), some 75% of ECM species are lost. In other words, there’s no significant difference between clearcutting and retaining 5% of the trees in terms of the effects on the number of fungal species lost. To preserve fungal diversity, many more trees must be retained when logging.

This study illustrates the unseen damage to forest ecosystems of intensive logging, as well as the potential challenges of re-growing forests following clear-cutting, given a likely dearth of ECM symbionts to aid sapling development.