Fungal Restoration in Cumbria

Mycorrhizal fungal inoculation

SPUN are playing a scientific role in a restoration project in Cumbria called Cumbria Connect. Cumbria Connect is a landscape-scale restoration which includes fungal inoculation to improve tree planting success: one project goal is to re-establish trees in designated valleys and hillsides. Many of the project areas are currently grassland being used for sheep grazing. Grassland soils lack the communities of mycorrhizal fungi that many tree species, including oak and birch, need to establish and grow. SPUN and Cumbria Connect are studying whether restoring mycorrhizal fungi alongside trees will improve restoration success. Restoration success means the percentage of trees which take root and grow. Because recent research highlights the importance of using local, adapted fungal communities, restoration is conducted with soil containing mycorrhizal fungi from Naddle Forest, which is located in the project area. This inoculation approach mimics natural fungal partnerships that trees need to thrive.

"Planting trees where the required mycorrhizal communities are absent is like completely stripping somebody of their microbiome...[and] unlikely to lead to establishment and long-term growth success."

Fungal restoration means re-introducing and encouraging healthy, native fungal communities such as mycorrhizal fungi into underground ecosystems.

SPUN is helping to monitor how mycorrhizal fungal communities change as the Cumbria Connect team carry out active restoration strategies such as grazing exclusion and restoration of scrub habitats. The results will inform restoration and replanting strategies. eDNA sequencing allows researchers to look into the underground and see which mycorrhizal fungi are present, and how fungal communities change alongside restoration practices. This is where SPUN comes in, taking baseline data and measuring change. SPUN’s goal is to produce scientific evidence to support and improve restoration techniques.

Research questions

1. Does inoculation of tree seedlings with whole soil inoculum improve tree establishment?

NOTE: Whole soil inoculum means the application of entire soil microbial communities from a donor site to a restoration area, as opposed to isolated single-strain commercial products. Mycorrhizal inoculation is the introduction of mycorrhizal fungi on plant roots or into target areas in order to establish symbotic relationships between plants and mycorrhizal fungi. Click here for a definition of mycorrhizal inoculation.

2. How do mycorrhizal communities change alongside aboveground active restoration practices?

Hypothesis:

A significant barrier to restoration success is mycorrhizal mismatch. In this case, grassland soils are dominated by arbuscular mycorrhizal fungi (AMF) while many target temperate tree species in Cumbria, including oak and birch, depend on ectomycorrhizal fungi (ECM) partners. Mycorrhizal fungi are one of the hidden variables which may explain why visually similar sites end up with different outcomes during restoration. Ancient woodlands are reference conditions for the fungal community which projects may be trying to recover, and so are candidate sources of local inoculum.

The Cumbria Connect nursery experiment is especially valuable because it is designed to answer a question practitioners often ask but are rarely able to test: does local woodland soil improve tree planting success?

Location

Cumbria is a region in North West England. The mountainous Lake District (a UNESCO World Heritage Site) is located in Cumbria. Cumbria Connect is restoring natural processes across about 34,000 ha in northwest England through woodland, peatland, and grassland restoration, habitat connectivity, and species recovery.

Partners

Cumbria Connect is an RSPB (Royal Society for the Protection of Birds) project, and one of the projects within the Endangered Landscapes and Seascapes Program.

Project summary

This project is a practitioner-oriented example for restoring trees, soils, and belowground recovery across upland pasture-to-woodland transitions. And an example of monitoring mycorrhizal fungal communities across different habitats to identify a mycorrhizal starting point, so that practitioners can identify where passive restoration is sufficient and where active fungal intervention may be necessary. Cumbria illustrates a common restoration problem: aboveground woodland creation is being attempted on landscapes whose soils are still organized around long-grazed grassland communities. In this setting, mycorrhizal restoration is not a standalone intervention. It is a practical way to improve site selection, refine nursery and planting practice, and monitor whether the belowground system is moving from pasture conditions towards a functioning woody mosaic.

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Landscape Scale Restoration

Cumbria is a landscape scale restoration project. This means restoring a large area, a mosaic of habitat types; wetlands, areas around rivers, hillsides, and forest cover. A large landscape is  valuable because it restores multiple components and connects habitats. The RSPB wants to show that farming and food production are compatible with restoration and rewilding; we can support biodiversity and produce good food. Livelihoods and culture also play a role, as Cumbria is in the Lake District, and a UNESCO world heritage site.

The project area includes peat bogs and scrub at the top of the hills (fells), grazed grasslands on hillsides, and fragments of ancient temperate rainforest. A large part of this project involves restoring temperate rainforests. This is a now-rare ecosystem; Atlantic rainforest.

The project wants to explore how mycorrhizal fungi can help restore bare hillsides to fragments of temperate rainforest. Inoculating with specific native soil is intentional active restoration: taking soil from the existing patch of oak and birch forest in Naddle Forest. Taking soils known to contain specific mycorrhizal fungi associated with oak and birch. We know oak and birch specifically are very reliant on ecto-mycorrhizal fungi. The plan is to inoculate saplings of oak and birch growing in a nursery, ready to plant out on the hillside. We're hoping it will improve the success of those trees when we plant them out from the nursery to hillsides.

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There haven't been trees since the Bronze Age in many areas of Cumbria. This tends to mean that the mycorrhizal fungi that support many temperate tree species are absent from these soils. Planting of these species that are dependent on mycorrhizal fungi may therefore suffer from reduced success rates.

People are increasingly turning to mycorrhizal fungi, and suggesting that an explanation of low success rates is the lack of established mycorrhizal networks in the soil. In order to identify the correct partners to the specific plant species intended for establishment, it's important to consider the mycorrhizal fungal communities that are currently present, and the mycorrhizal fungal communities that are required to support the target vegetation.

Planting trees where the required mycorrhizal communities are absent is like completely stripping somebody of their microbiome. This is unlikely to lead to establishment and long-term growth success.

However, further scientific evidence and knowledge is needed to fully understand how restoring mycorrhizal communities can be used to support restoration aboveground. So that's what we're doing in Cumbria: we're producing science in a restoration context, working alongside experienced practitioners who understand the landscape and have specific restoration goals. We are advancing our understanding of how restoration works and how it can be improved using ecological science. We're generating knowledge that other restoration projects and practitioners can use, which is one of our goals.

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Project Design: Treatment and Methodology

In order to begin restoring the fungal communities in a site, we must first understand what is currently present. This is called baselining, and is required to understand the communities of mycorrhizal fungi that currently occupy a site.

One part of the project in Cumbria is baselining the Mardale Grazing experiment, a long-term restoration experiment set up by the RSPB that consists of a large mosaic hillside comprised of block systems. Grazing by deer or cattle is excluded from certain treatment blocks to allow for natural regeneration, and active replanting is practiced in others. We want to see which mycorrhizal fungi are currently there and which species and communities start to come back or emerge with these treatments, and how quickly that happens.

Reforestation and afforestation, the creation of woodland where none currently exists, is an important practice across many countries. Many practitioners want to improve the success rate of tree replanting, especially of oaks and birches, key species in the restoration of the UK’s Atlantic rainforest habitat. As these are ectomycorrhizal hosts, SPUN and the RSPB are exploring how to ensure that this microbiome of fungi is present in the soil for the trees being planted on the treeless hillsides of Cumbria.

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Technique

We are using soil from an existing fragment of Atlantic rainforest local to the replanting sites, where established oak and birch trees and their mycorrhizal symbionts already exist. We therefore know that the mycorrhizal fungi in these soils are the partners of these trees, and are locally adapted.

This technique of transplanting soil microbiomes is well established, and we're trying to develop evidence that this works in individual restoration contexts. We want to measure and quantify how important restoring mycorrhizal communities is to tree establishment and growth, and how mycorrhizal fungal communities develop and change over time in restoration contexts. We will use this information to further develop and inform belowground restoration practices in further projects.

Mycorrhizal mismatch is a potential barrier to success. Long-grazed pasture soils are typically dominated by arbuscular mycorrhizal pathways associated with grasses, while many target temperate tree species in Cumbria, especially oak and birch, depend strongly on ectomycorrhizal partners. If these fungal partners are sparse or absent, tree establishment may be contingent on nearby inoculum sources.

This does not imply that every failed planting is a fungal failure. Herbivory, soil quality, drainage, propagule pressure, and planting stock quality still matter. But mycorrhizae are one of the hidden variables that can explain why visually similar sites produce different outcomes and why tree cover alone is not a sufficient measure of restoration progress.

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Conclusion

This project and its findings matter beyond Cumbria. Across the UK uplands and many other pasture-to-woodland transitions, managers are trying to rebuild woodland on soils that have been simplified by grazing, nutrient legacies, and the loss of fungal-host partnerships. This case study shows how mycorrhizal restoration can move from an understanding that mycorrhizal fungi are important to tree hosts, to an operational framework: diagnose the current situation, match host and fungal strategy, source inoculation safely and locally, and monitor belowground recovery as a restoration outcome in its own right.

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