The role of mechanized harvesting in the development of bluestain in pine

The influence of mechanized harvesting on the development of bluestain was assessed by comparing pine logs felled and trimmed with a chainsaw with those felled by a commercial harvesting machine. Corsican pine (Pinus nigra var maritima (Ait.) Melville) grown in the United Kingdom was cut in June and August, and the logs were assessed for bluestain 3, 6, 9, and 12 weeks after felling. Mechanically harvested logs were in two groups: maximum damage (mean amount of bark loss ~35% of total cover) and minimum damage (~12% mean bark loss). However, all mechanically harvested logs were much more susceptible to attack by bluestain fungi than chainsaw-processed logs, which typically had <1% bark loss. Mechanically harvested logs had bluestain on ~10% of the surface area of sample discs compared with <1% in the chainsawharvested logs. Little bluestain developed if bark loss was <10%. The most extensive stainers were Ceratocystis coerulescens (Münch) Bakshi and Leptographium wingfieldii Morelet; other frequent bluestain fungi included Ophiostoma piceae (Münch) H. & P. Sydow, Sphaeropsis sapinea (Fr.) Dyko & Sutton, and a Graphium species. Bluestain bark beetle vectors were excluded from the logs, but other arthropods apparently acted as vectors. Using data from the study, a model was devised to predict of stain development following a known amount of bark damage.