Diversity and ecology of aphyllophoroid fungi on driftwood logs on the shores of the Baltic Sea

Driftwood is woody debris that is floating on the sea or brought onto the shore by the sea. It can have a natural origin but often it originates from human activities. Driftwood has a significant ecological role as a microhabitat for a large range of species. Dead-wood-associated aphyllophoroid fungi on driftwood have been studied rather little globally, and there are hardly any studies conducted in the Baltic Sea. We studied the diversity and ecology of polypores and corticioids growing on driftwood (man-made logs) on the shores of the Finnish SW-archipelago. In total, 394 driftwood logs were surveyed for visible fungal sporocarps. We found altogether 145 species (1023 records) of which approximately three-fourths were corticioids. The driftwood logs hosted several rare and noteworthy species, such as one new corticioid species, 16 nationally rare species, and 40 new species to the region. The five most common species accounted for one-third of all observations, whereas 82 species (11% of all records) were recorded only once or twice. Larger logs hosted, on average, more species compared to small-diameter logs. The mean number of species increased significantly when comparing the logs in the first and the middle stages of decay. Our results show that driftwood logs can host a wide variety of species and they provide an important substrate for many dead-wood-associated fungi, including species of conservation concern and species with restricted ecological requirements. Driftwood hosted several species that have not been previously found in the archipelago forests, and the logs clearly enrich the fungal diversity in the area. Our results encourage to increase dead wood for fungi in coastal forests where it has been dramatically decreased as a result of strong hemeroby.