Root rot

Root rot, caused by fungi of the genus Heterobasidion, is one of the most economically damaging diseases in temperate forest ecosystems. This necrotrophic pathogen primarily targets the root system and the lower bole, causing decay that leads to significant timber volume loss and tree mortality.

The disease has a wide host range, with conifers being the most vulnerable. Species such as Norway spruce, Scots pine, and various firs are particularly susceptible. In dense plantations, the pathogen spreads rapidly, causing tree death and creating gaps in the forest canopy that can expand over several decades.

Symptoms of an infection often include crown thinning, needle discoloration, and a stunted annual growth rate. In advanced stages, trees may show resin exudation near the base of the trunk. Because the root system is degraded, affected trees are frequently windthrown even during moderate weather events, posing a risk to forest stability.

The fungus spreads via basidiospores landing on fresh stumps or wounds, as well as through direct root-to-root contact between infected and healthy trees. Environmental conditions such as moderate soil moisture and specific temperature ranges facilitate the growth of the mycelium, making some sites more prone to infection than others.

Effective management strategies focus on prevention and silvicultural control:

• Stump treatment with biological control agents like Phlebiopsis gigantea immediately after harvesting.
• Minimizing soil compaction and root damage during thinning operations.
• Promoting species diversity to reduce the rate of pathogen spread between hosts.
• Monitoring forest stands to detect and remove infected centers early.