Bjerkandera

Bjerkandera is a genus of fungi within the Meripilaceae family, recognized primarily for causing white rot in various hardwood species. The most common species, Bjerkandera adusta, acts as a saprotroph and occasional pathogen, effectively degrading lignin and cellulose within the host structure. This degradation leads to the progressive weakening of the tree's mechanical integrity.

This fungus typically affects broad-leaved trees, including birch, beech, oak, lime, and maple. While it thrives on dead wood and fallen logs, it can also infect living trees through open wounds, pruning cuts, or damage caused by environmental factors like frost or wind. By colonizing the woody tissue, it disrupts nutrient flow and compromises the overall health of the tree.

Symptoms of Bjerkandera infection include the presence of fruit bodies, which appear as thin, leathery, shelf-like structures on bark. These caps are usually greyish-brown with a distinct dark or scorched-looking edge. When the wood is split, the infected internal structure shows signs of white rot—the wood becomes pale, soft, and fibrous, losing its structural strength significantly over time.

The development and spread of the fungus are heavily dependent on environmental conditions, specifically high humidity and moderate temperatures. Spores are released from the fruiting bodies and dispersed by wind or splashing rain. Once they land on a vulnerable or wounded area of a tree, they germinate, initiating the colonization process within the vascular and structural tissues of the host.

The impact of Bjerkandera is notable in both natural forest ecosystems and managed urban landscapes, as it increases the risk of structural failure and windthrow of infected trees. Effective management involves rigorous sanitation, such as removing heavily infested wood, protecting trees from physical injury, and ensuring that trees are not subjected to chronic stress, which makes them more susceptible to fungal colonizers.