How can tree retention mediate the effects of human-introduced disturbance on ectomycorrhizal fungi? Nahuel Policelli  and Senior Editor, Martin Nuñez discuss the recent article, The significance of retention trees for survival of ectomycorrhizal fungi in clear‐cut Scots pine forests.

One of the most important above-belowground interactions is that between plants and mycorrhizal fungi. Acting as symbionts, mycorrhizal fungi are involved in plants’ nutrient uptake and water acquisition as well as protection against pathogens. They also take part in processes at a broader ecological scale: they contribute to plant diversity and community assembly, affect nutrient cycling and are fundamental at ecosystem functioning. Due to their key position at the plant-soil interface, mycorrhizae can be highly affected (both positively and negatively) by any human introduced change in environments.

Our understanding of how belowground communities, including mycorrhizal fungi, are impacted through human-introduced practices that affect the soil is just beginning. In a previous blog post, we discussed the importance of considering belowground communities in plant restoration and management plans, highlighting that it is not possible to restore plant communities without considering belowground organisms. Here our aim is to further discuss how certain management techniques can take into account the complexity of human-impacted ecosystems by acknowledging the role of soil biota. This is based on the recent work by Sterkenburg et al. that highlights the need to keep host trees to maintain mycorrhizal abundance and diversity.

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Retention forestry, a practice that has been implemented in forest management since just a few decades ago, is an alternative to clearcutting, by which a portion of the original stand is left unlogged to maintain the continuity of structural and compositional diversity. Human-introduced disturbance provoked by forestry can greatly differ from natural disturbance in terms of effects on the ecosystem. Retention forestry has emerged as a response to the rapid ongoing modification and simplification of forest ecosystems. It is therefore recognized, not only as a way to conserve the structural, functional and compositional diversity of forest ecosystems, but also as a useful tool for the restoration of impoverished or degraded forests. Mycorrhizal fungi are within the organisms that benefit the most from tree retention ( see Rosenvald & Lohmus, 2008). In their recently published paper Sterkenburg et al. asked how the amount of retention trees relates to the maintenance of ectomycorrhizal fungal biomass and diversity during time following forest harvest.

The approach of Sterkenburg et al. considers the idea of preserving not only the set of organisms that are part of the interaction (plant host and ectomycorrhizal symbiont) and that are somewhat partially independent, but also the interaction itself – increasing our understanding of the possible implications of retention forestry. The authors present hard evidence that clearcutting in Scots pine forest in North Sweden directly affects the community of ectomycorrhizal fungi (EMF). They found that fungal species abundance and richness depend on the amount of host trees retained and that retention trees are capable of maintaining EMF biomass and diversity up to three years following forest harvest. Interestingly, even when clearcutting causes EMF communities to be strongly impoverished, there is a set of common EMF species that survive harvest. These EMF may have a set of ecological traits that allow them to resist increasing logging. Furthermore, the more trees that are retained, the higher richness of EMF is preserved, as less frequent fungal species are maintained.

Sterkenburg et al.’s results have implications for both fungal ecology and forest restoration. To evaluate whether this pattern of mycorrhizal diversity is consistent in other managed forest systems, future studies should be performed in tropical and temperate forests in which the practice of retention forestry is increasingly being implemented. Future research may also shed light into changes in the fungal community provoked by human-introduced practices that may be independent of changes in the plant community. Clearcutting, for example, could be greatly affecting hyphal links and disassembling the mycorrhizal network present in the soil which would in turn affect future restoration efforts of logged areas. Finally, although short-term studies are necessary, extrapolation of results obtained by short-term studies is often tricky. Whenever possible, long-term responses to management techniques should be addressed using natural experiments that validate short term results. On the way forward it seems inevitable to take into account the role of soil biota in management practices. Keeping mutualistic fungi by keeping their plant hosts is another example of how successful results of management techniques are highly conditioned by belowground organisms.

Read the full article, The significance of retention trees for survival of ectomycorrhizal fungi in clear‐cut Scots pine forests in Journal of Applied Ecology.