A single ancient tree in southern Chile, estimated to be more than 2,400 years old, harbors more than twice the underground fungal diversity found beneath younger saplings nearby. The finding, drawn from soil samples collected beneath 31 individual Fitzroya cupressoides trees, suggests that the largest and oldest specimens in these slow-growing rainforests serve as disproportionate anchors for the microbial communities that keep the ecosystem functioning. As warming and drought increasingly threaten the carbon-storing capacity of these forests, the discovery adds urgency to understanding what lives beneath them.
Mapping Fungi Beneath Millennial Trees
The peer-reviewed study, published in Biodiversity and Conservation, sampled soils beneath 31 Fitzroya cupressoides individuals, according to the journal. The trees ranged from young saplings to the famed “Alerce Abuelo,” a specimen estimated to be roughly 2,400 years old. Fitzroya cupressoides, commonly known as alerce, is a conifer native to Chile and Argentina that grows at an exceptionally slow rate and exhibits very low mortality, per institutional summaries of the research.
To catalog the hidden fungal communities, the research team used soil metabarcoding with ITS2 genetic markers for broader soil fungi and SSU markers specifically for arbuscular mycorrhizal fungi, according to the study. These DNA-based techniques allowed the researchers to identify hundreds of fungal species from soil alone, without needing to observe fruiting bodies above ground. The approach revealed that large-diameter trees like Alerce Abuelo host more than twice the underground fungal diversity of smaller, younger trees in the same forest.
The authors also highlight that most previous soil fungal surveys have focused on ectomycorrhizal forests in the Northern Hemisphere. By contrast, the alerce stands in Chile’s temperate rainforests are dominated by arbuscular mycorrhizal associations, making them an important counterpoint for understanding how different kinds of fungal partnerships respond to environmental change.
That gap in diversity between old and young trees is not simply a curiosity. It points to a structural feature of these forests: the oldest trees are not just storing carbon in their wood. They are actively maintaining a richer underground community of organisms that, in turn, helps the broader forest withstand environmental stress.
Why Root Fungi Matter for Tree Survival
Mycorrhizae, the partnerships between fungi and plant roots, are among the most widespread biological relationships on Earth. These are fungus-root associations in which colonization of roots by mycorrhizal fungi benefits the host tree by improving access to water and nutrients. In return, the fungi receive carbohydrates produced through photosynthesis. The arrangement is mutual, and for trees growing in nutrient-poor or drought-prone soils, it can mean the difference between survival and decline.
The alerce study builds on this basic biology by showing that not all trees contribute equally to sustaining these fungal networks. Soil fungi play major roles in ecosystem functioning and plant resilience to environmental stresses, but most prior research on these relationships has been conducted in forests dominated by ectomycorrhizal tree species in the Northern Hemisphere. The Chilean alerce forests represent a different and far less studied system, one where individual trees can persist for millennia and where the relationship between tree size, age, and belowground biodiversity had not been quantified until now.
One common assumption in forest ecology is that protecting canopy coverage is sufficient to preserve biodiversity. The alerce findings challenge that idea. If the oldest, largest trees are disproportionately responsible for fungal diversity underground, then losing even a few of those individuals could trigger a decline in soil health that ripples through the entire stand. Younger replacement trees simply do not host the same breadth of microbial life, at least not for centuries.
Climate Threats to an Ancient Carbon Sink
The stakes extend well beyond fungal taxonomy. Fitzroya cupressoides rainforests sit in Chile’s Coastal Range, where separate research has tracked their response to warming and drying conditions. Carbon flux measurements conducted from February 2018 to January 2021 using eddy covariance and chamber techniques found that these forests are sensitive to warm and dry conditions, with seasonal patterns that weaken their capacity to absorb carbon, according to a study indexed in PubMed.
Alerce forests grow slowly and die rarely. According to institutional reports summarizing the new research, one alerce tree lived more than 3,600 years, making the species one of the longest-lived on the planet. That extreme longevity means these forests store carbon over timescales that dwarf most other ecosystems. But it also means they recover slowly from disturbance. A drought severe enough to kill mature trees could erase centuries of accumulated carbon and the fungal communities that supported those trees.
The tension between the forests’ slow pace and the accelerating pace of climate change is the central problem. If warming continues to erode the carbon sink capacity of these rainforests, the underground fungal networks documented in the new study could be among the first casualties, weakening the trees’ ability to cope with stress precisely when they need it most. Loss of fungal diversity could also make regeneration less reliable, as seedlings without robust mycorrhizal partners struggle to establish in increasingly harsh conditions.
Microbial Conservation Goes Global
The implications of the alerce work resonate with a broader push to protect the world’s unseen biodiversity. Microbial ecologists have called for coordinated efforts to safeguard Earth’s terrestrial microbiome, arguing that soil organisms underpin food security, climate regulation, and ecosystem resilience. In that framework, ancient trees like Alerce Abuelo become keystone hosts for entire microbial communities, not just charismatic organisms in their own right.
Other recent studies underscore how sensitive these underground networks can be. Experimental work in temperate systems has shown that shifts in temperature and moisture can rapidly alter the composition of root-associated fungal communities, with cascading effects on plant performance. In parallel, long-term observations have documented how changing climate and land use reshape forest soil microbiomes, sometimes in ways that reduce their ability to buffer ecosystems against stress.
Scientists working across continents are beginning to connect these dots. At institutions such as the Royal Botanic Gardens Victoria, researchers including Camille Truong study how fungal symbionts vary among tree species and habitats, and how that variation might influence conservation priorities. The emerging picture is that protecting iconic tree species without accounting for their microbial partners risks overlooking a major part of what makes those trees resilient.
Protecting Microbial Allies, Not Just Trees
E. Toby Kiers, an author on related work advocating for conservation of Earth’s terrestrial microbiome, has argued that soil microbes should be treated as critical infrastructure for the planet’s life-support systems. The new alerce research gives that argument a concrete case study: a single, massive tree supporting a uniquely rich fungal community that, in turn, supports the surrounding forest.
For conservation planners, this suggests several practical steps. First, management plans for alerce reserves may need to prioritize the protection of the very largest individuals, not only because of their age and carbon stores but also because of their role as hubs in the underground network. Second, restoration projects that plant young alerce saplings should consider the fungal context, whether by preserving intact soil from old-growth stands, minimizing disturbance around remnant giants, or designing experiments to test how different management actions affect soil communities over time.
The study also raises questions that will require further work. Do similarly old and large trees in other parts of the world, from North American redwoods to ancient African conifers, host comparable spikes in fungal diversity? How quickly do those communities collapse if a giant tree dies, and can they be rebuilt? And at what spatial scale do these effects operate. Are they confined to a few meters around the trunk, or do they influence entire hillsides?
What is clear is that the forest beneath our feet is every bit as intricate as the forest above. In Chile’s temperate rainforests, an ancient conifer has revealed just how much life can gather around a single trunk, given enough time. As climate change tightens its grip, the survival of those millennial trees, and the fungi entwined with their roots, may determine whether these ecosystems continue to function as stable carbon sinks or tip toward long-term decline.
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*This article was researched with the help of AI, with human editors creating the final content.
