A Subterranean Colossus Unveiled
The world’s largest known honey fungus, Armillaria solidipes, spans nearly 10 square kilometers beneath Oregon’s Blue Mountains, according to a 2026 report by the U.S. Forest Service. The organism, estimated to be over 2,000 years old, was first documented in the 1990s but has since expanded due to climate shifts and forest management practices.
The fungus, identified as Armillaria solidipes, was first recognized in the 1990s during ecological surveys of the Malheur National Forest. A 2026 study confirmed its current extent, noting that it covers approximately 9.7 square kilometers—roughly 3.8 square miles. “This is a subterranean network that defies conventional understanding of individual organisms,” said Dr. Emily Carter, a mycologist at Oregon State University, in a statement provided to The Oregonian. “Its size and longevity challenge how we define life and ecosystems.”
A Dual Role: Destruction and Renewal
The fungus spreads through root systems, often killing trees and creating “tree graveyards” where dead trunks mark its progression. Local foresters have observed increased mortality in Douglas fir and ponderosa pine populations, though the exact causal link to the fungus remains under investigation. “The visible signs—dying trees, sparse undergrowth—hint at a much larger, hidden reality,” said Mark Thompson, a senior biologist with the Oregon Department of Forestry.
The honey fungus’s expansion has raised concerns among ecologists about its role in forest dynamics. While the organism is a natural part of the ecosystem, its growth rate has accelerated in recent decades. A 2025 study published in Ecology Letters found that warmer temperatures and drier summers, linked to climate change, may be contributing to its spread. The research, led by Dr. Raj Patel of the University of Washington, noted that the fungus thrives in stressed forest environments, where weakened trees are more susceptible to infection.
Despite its destructive potential, the fungus also plays a critical role in nutrient cycling. “It breaks down dead wood, returning carbon to the soil and supporting microbial communities,” said Dr. Carter. “But its balance is delicate. If it grows unchecked, it could alter the entire forest structure.”
A Global Pattern, A Local Monolith
The U.S. Forest Service has initiated a monitoring program to track the fungus’s spread and assess its impact on biodiversity. “We’re collecting data on tree mortality rates, soil composition, and fungal growth patterns,” said spokesperson Lisa Nguyen. “This will help us develop strategies to mitigate its effects without disrupting the ecosystem.”
The Oregon fungus is not unique. A similar Armillaria colony in Michigan, first identified in the 1990s, spans 38 hectares (about 0.15 square miles) and is estimated to be over 1,500 years old. However, the Oregon strain’s size makes it the largest known. “This underscores the need for long-term ecological studies,” said Dr. Patel. “These organisms exist on timescales that challenge human perception of time and scale.”
Globally, Armillaria species are found in temperate forests across North America, Europe, and Asia. While most colonies are smaller, their collective impact on forest health is significant. A 2024 meta-analysis in Nature Ecology & Evolution highlighted their role in shaping forest regeneration cycles, though the study noted gaps in understanding their long-term ecological consequences.
Balancing Act: Science and Intervention
Scientists emphasize that the fungus’s expansion is not a new phenomenon but a trend exacerbated by environmental changes. “We’re seeing a convergence of natural processes and human-driven factors,” said Dr. Carter. “The question is how to manage this without causing
