Is Reforesting Farmland All It’s Cracked Up To Be? The Story Told By Fungi

Cross section of microbial fungi in forest floor
Cross section of microbial fungi in forest floor

Summary

There’s a lot we can learn from mushrooms. Fungi offer a fascinating glimpse into the resilience and complexity of nature, providing numerous lessons in ecology, biology, and even technology. But for those of us who are major forestry nerds, they can also tell us about the health of our tree-planting projects.  

A recent study in “Environmental DNA” takes a look at an increasingly popular type of project: reforesting farmers’ fields. Soil fungi are good at helping fix up places where the environment has been damaged, but we don't know much about how they come back to areas overused for farming or where there have been too many deer. To figure this out, the authors used DNA metabarcoding to study the types of fungi in places where trees have been planted after farms were abandoned and areas overrun by deer. They found that in places where trees have been replanted, there are about 2 to 3 times more types of fungi compared to untouched forests, no matter how many different kinds of trees were planted. However, these replanted areas ended up having a more uniform mix of fungi across the board, which means there wasn't as much variety in the types of fungi from one area to another within these planted forests. This was probably because the environment was more similar throughout these areas, fungi didn't spread as widely, and these areas haven't been growing back for very long. Keeping deer out didn't appear to change the mix of fungi they found.

The Legacy of Historical Land Use

Overall, it looks like the impact of past farming on the types of fungi in the soil sticks around for a long time, even when we try to fix the surface by planting trees. So, we need to be mindful of the soil itself to help bring back a full range of soil life that's been changed.

The study of fungal communities and their richness in forests is not only important for understanding ecosystem processes but also for conservation efforts. Fungi serve as bioindicators of forest and soil health, and changes in their diversity can signal shifts in ecosystem functioning due to natural disturbances or human activities. Therefore, maintaining fungal diversity is essential for sustaining forest ecosystems' resilience and productivity.

Analyzing Soil Fungal Communities

Using advanced environmental DNA (eDNA) techniques, the study analyzed soil samples from areas with varying histories of agricultural use and ungulate presence. Comparisons with undisturbed areas helped quantify how these historical changes continue to impact soil fungal diversity and functionality.

The data here arranges fungal OTUs in decreasing order based on their frequency of occurrence across different sites. This ranking helps in identifying which OTUs are more common versus those that are rare within each treatment group.

The Akaike Information Criterion (AIC) is used to select the best-fitting model for the data. AIC is a widely used measure of a statistical model's quality. It deals with the trade-off between the goodness of fit of the model and the complexity of the model. The model with the lowest AIC value is typically considered the best fit because it offers the right balance between simplicity and the ability to explain the variation in the data.

Enhancing Land Restoration

It’s fascinating to see these results from a study that took place in Northern Japan in 2013. It would also be interesting however to see data sets from other countries, with different climates. What would a similar experiment look like in a tropical environment for example? More data sets from different countries can expand our knowledge of how soil health corresponds with land preparation type. 

Open Data & Code

Raw sequence data files are available at the DNA Data Bank of Japan (DRA003024). Fungal community matrix (OTU ×sites), species’ functional groups, the list of literature we used to determine the functional groups, and consensus sequences are archived in Dryad Digital Repository: https://doi.org/10.5061/dryad.02v6wwq2w (Tatsumi et al., 2021).

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