Old forest is continuity, not a pile of fresh logs

Deadwood is a fundamental resource for thousands of fungi, but the number of cubic metres alone does not describe the full quality of a forest. A study of Central European mountain spruce forests combined an inventory of fruiting bodies with measurements of the volume, dimensions and decay stages of wood. The stand's history was reconstructed dendrochronologically, checking among other things the number of trees older than 250 years.

Total richness of wood-inhabiting fungi correlated best with the amount of lying wood and low stumps. Richness of red-listed species, however, responded more strongly to habitat continuity, indicated by the presence of the oldest trees that had survived earlier management. The result undermines a simple prescription: leaving a few fresh logs in a young stand is necessary, but it does not immediately create the conditions of a forest with an unbroken history.

Different species colonise wood of a particular species, size, moisture content and stage of decay. They also need a source of spores within reach in the landscape. Continuity therefore acts as a record of many overlapping conditions, not as a mystical age of a place. Protection should safeguard old trees, standing and lying wood, a range of decay classes and a humid microclimate.

In forest management this means retention planned over decades and centuries. The most valuable fragments should not be treated as a store that can be cut and recreated with an equal number of logs elsewhere. Monitoring of fruiting bodies is worth combining with a map of the stand's history. The absence of a fruiting body in one season does not prove disappearance, but a loss of continuity may be effectively irreversible on the scale of a human life.

What the field study separated

Researchers used thirty permanent 1,000 m² plots in old-growth mountain Norway-spruce forest in Central Europe. They surveyed wood-inhabiting fruit bodies and deadwood decay, while dating trees dendrochronologically. Total species richness was best explained by lying deadwood and low-snag volume, while red-listed richness was best explained by the number of trees older than 250 years, used as a continuity indicator after historic logging. Adding substrate may raise overall richness but cannot instantly recreate the rare specialist assemblage. This was an observational study in one forest type, and “over 250 years” is a local history indicator, not a universal biological threshold. Absence of a fruit body should not be equated with absence of mycelium.