A decaying pine log colonised by multiple organisms. Pink staining inside the wood indicates extensive fungal mycelial growth, while several lichen species appear on the log surface. Most fungal biomass remains hidden within the wood, where it can be detected using DNA-based methods. Photo: Vincent Buness, SLU.
A decaying pine log colonised by multiple organisms. Pink staining inside the wood indicates extensive fungal mycelial growth, while several lichen species appear on the log surface. Most fungal biomass remains hidden within the wood, where it can be detected using DNA-based methods. Photo: Vincent Buness, SLU.

Rare boreal deadwood fungi do not recover in clear-cut forests

News published:  20/03/2026

Managed boreal forests support far less diverse fungal communities compared to successional forests sprung from forest fires. A new study from the Swedish University of Agricultural Sciences shows stark differences in the abundance of rare species between environments of different forest regimes.

The study, published in Journal of Ecology, paints a clear picture: in forests originating from wildfire disturbance, the amount of fungal species continues to increase as the forest grows older. In managed forests, however, the species richness is much lower, and lags behind over time.

– Over their lifetime, managed clear-cut stands remain far below the diversity observed in unmanaged forests, says PhD student Vincent Buness at the Department of Forest Ecology and Management, lead author of the study.

The researchers systematically surveyed 36 forest sites in northern Sweden for fungal species, areas which varied in time since the last harvest or fire. Through field surveys and hundreds of DNA-analyses of dead wood, they charted the species richness of both visible and hidden fungal communities.

The study compared managed forests of up to 109 years of age with fire-disturbed forests, some of which were much older. Especially for red-listed species, the species diversity was significantly higher in the unmanaged forests. Figure: Vincent Buness, SLU.
The study compared managed forests of up to 109 years of age with fire-disturbed forests, some of which were much older. Especially for red-listed species, the species diversity was significantly higher in the unmanaged forests. Figure: Vincent Buness, SLU.

The differences they found between stand types were stark, especially for rare, red-listed fungal species. On average, the unmanaged fire-origin stands had around 55 more total species than managed clear-cut stands at comparable ages (≤109 years). And the gap grows over time. When looking at even older fire stands, the researchers found ~156 more species on average compared to the managed forests.

Dead wood maturing for centuries

The explanation can be found in the forest structure, as well as in time itself.

Many rare fungi are dependent on large diameter dead wood that has had time to decay very slowly. In northern Sweden, it can take decades, if not centuries, for a tree to reach the final stages of decomposition that some species need to thrive.

– A pine in northern Sweden can easily become 200-300 years old and remain standing for another 200 years after it dies. When it falls, it can take many decades to over a century until they are no longer visible in the forest, and some fungal species only appear once the logs reach very late decay stages, says Vincent Buness.

These old-growth dead wood environments are exceedingly rare. Across all 36 forests in the study, only 13 larger logs at this far end of decay were found in total.

Over time, clear-cutting and forest fires create forests with fundamentally different structures. The depicted stands represent key successional stages following disturbance and are visualized using terrestrial laser scanning in a 30 m radius around the plot centre (stands at the top row: 13, 42, and 100 years since clear-cutting, stands at the bottom row: 56, 121, and 375 years since fire). Figure: Vincent Buness, SLU.
Over time, clear-cutting and forest fires create forests with fundamentally different structures. The depicted stands represent key successional stages following disturbance and are visualized using terrestrial laser scanning in a 30 m radius around the plot centre (stands at the top row: 13, 42, and 100 years since clear-cutting, stands at the bottom row: 56, 121, and 375 years since fire). Figure: Vincent Buness, SLU.

But forest fires can help create the necessary conditions: when the forest burns, trees of different species and ages are damaged, creating a mix of standing and lying dead wood. This forms the first link in an unbroken chain of environments where the fungal communities can establish themselves as the dead wood “matures”.

In managed forests, this process is cut short. Though thinning, clearing and harvesting, the dead wood becomes too scarce and too uniform to host the specialized fungal species over time.

Threatened species in the hundreds

Fungi play a vital role for many of the forest’s inhabitants, not least in helping many plants take up vital nutrients. At the same time, many fungal species are under threat, with more than 800 species appearing on the Swedish red list.

The new SLU study shows that dead wood volume alone is not enough to sustain and preserve these species. To give the most specialized fungi a chance to survive demands centuries of forest ecosystem development over time since disturbance.

– In essence, we can regrow forests, but we cannot create habitat continuity for wood-inhabiting fungi. Many fungal species depend on long, undisturbed periods of growth, death, and decay, sometimes spanning hundreds of years. When this continuity is broken, it cannot be easily recreated within typical forestry rotations, says Vincent Buness.

SLU-authors:

Vincent Buness, Department of Forest Ecology and Management

Maja Sundqvist, Department of Forest Ecology and Management

Michael Gundale, Department of Forest Ecology and Management

Marie-Charlotte Nilsson Hegethorn, Department of Forest Ecology and Management

Torbjörn Josefsson, Department of Forest Ecology and Management

Noel Ingre Weiser, Department of Forest Ecology and Management

Björn Lindahl, Department of Soil and Environment

Tamlyn K Gangiah, Department of Soil and Environment

In collaboration with co-authors from the Technical University of Munich and Umeå University.

Read the full paper

Distinct diversity trajectories of boreal wood-inhabiting fungi following fire versus clear-cutting (British Journal of Ecology, 2026) 

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