Why Chile’s 2,000-Year-Old Alerce Trees Have Become Magnets for Underground Fungi

The loss of one ancient Alerce tree could wipe out centuries of fungal diversity.

A new study reveals that Chile’s biggest and oldest Alerce trees (Fitzroya cupressoides) act as biodiversity vaults and support far more fungi beneath their roots than younger, smaller trees.

These hidden fungal communities help break down vast amounts of organic matter, cycle nutrients, and support numerous plants. This means that losing an Alerce tree could also mean losing a rich underground ecosystem it has supported for centuries.

Moreover, some of the Alerce trees have survived for more than 3,600 years and are hailed as the second-longest-lived tree species on Earth after the Great Basin bristlecone pine, which is known to live for over 5,000 years. But some Alerce could actually be the oldest trees in the world.

In 2023, Jonathan Barichivich and Antonio Lara estimated Chile’s Gran Abuelo to be about 5,484 years old, with an 80% probability of being older than 5,000 years, potentially making it the world’s oldest living non-clonal tree. They combined a partial tree-ring core containing roughly 2,400 years of growth with growth records from other Fitzroya cupressoides trees and statistical modelling of the missing inner trunk, though their results have yet to be verified independently.

Yet these ancient trees are increasingly vulnerable to habitat destruction, climate change, and wildfires, putting both them and the hidden communities they support at risk. 

“Alerce is currently listed as endangered in the IUCN Red List of threatened species, with only 40% of its distribution occurring within national protected areas. It is currently facing major threats in the Chilean Coastal Range due to habitat destruction from road development and increased wildfires due to climate change,” the study authors note.

Looking beneath the oldest trees

Scientists have long known that old trees can have an outsized influence on forest ecosystems, but much of the research has focused on what happens above the soil. The new study instead looked at whether a tree accumulates a richer underground fungal community as it grows older and larger.

To investigate this, researchers collected soil samples beneath 31 Alerce trees in the Chilean Coastal Range, including saplings, medium-sized trees, and large old-growth individuals. One of them was the famous Alerce Abuelo, estimated to be more than 2,400 years old.

The team measured each tree’s diameter at breast height (DBH) along with its height and biomass. Alerce Abuelo stood out dramatically. 

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Its DBH was 470 centimeters, more than three times that of the second-largest tree sampled, while its estimated biomass was more than 12 times greater.

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The researchers then turned to DNA. Instead of trying to identify every fungus by looking at it, they extracted genetic material from the soil and used a technique called metabarcoding. 

Two genetic markers were used: ITS2 to examine the broader soil fungal community and SSU to specifically examine arbuscular mycorrhizal (AM) fungi.

Tracing the fungal diversity

AM fungi are particularly important because they live closely with plant roots. They help plants obtain nutrients and can improve their ability to cope with environmental stresses. In return, plants provide the fungi with carbon.

The researchers also compared several DNA reference databases. This was important because fungal DNA databases are incomplete, meaning the same genetic sequence can sometimes be difficult to assign accurately to a particular fungal group.

The results revealed a striking pattern. Soil fungal richness increased with tree diameter, biomass, and height. 

“Beneath the Alerce Abuelo, soil fungal richness was 2.25 times higher than the mean richness per sample, harboring 361 unique fungal OTUs. Likewise, arbuscular mycorrhizal (AM) fungal richness was 1.75 times higher than the mean richness per sample,” the study authors said.

The oldest giant also had 361 fungal operational taxonomic units, or OTUs, unique to its soil samples. OTUs are groups of DNA sequences used as proxies for distinct organisms or taxonomic units. The researchers found that large trees generally supported significantly greater overall soil fungal richness than medium trees and saplings.

“Not all trees are the same, and if you remove a millennial tree, the impact on all the other species is going to be bigger than if you remove a smaller one,” Camille Truong, one of the study authors and a scientist at the Society for the Protection of Underground Networks (SPUN), said.

The soil itself also mattered. Available phosphorus was negatively associated with fungal richness and emerged as the strongest predictor of fungal community composition. In simple terms, fungal diversity tended to be higher where phosphorus was less available.

An underground legacy worth protecting

Over centuries or even millennia, a large Alerce can accumulate a distinctive fungal community around its roots, effectively creating an underground reservoir of biodiversity. This makes the enormous tree more than an old piece of forest. It may be providing a long-established home for organisms that younger trees have not yet accumulated.

“By accumulating fungal diversity as they age, large-diameter Alerce trees can act as umbrella species for soil and mycorrhizal fungi, thereby protecting fungal communities for future forest restoration efforts,” the study authors said.

Protecting them could therefore protect many organisms that are easy to overlook but are involved in nutrient cycling, plant productivity and resilience.

The finding is particularly relevant because Alerce forests have already lost much of their former range, while the trees themselves grow slowly and cannot simply be replaced after being cut down. 

The study therefore adds another reason to preserve the largest remaining individuals.

The findings appeared in Springer Nature’s journal Biodiversity and Conservation.