Abstract
A long time has passed since it became clear that the so-called "pine withering" phenomenon actually represented large-scale pine deforestation throughout Japan. However, because the implementation of countermeasures against the vector of the pine wood nematode, Bursaphlenchus xylophilus, has failed to halt the progress of deforestation, the mechanism remains unclear. On the other hand, a strong correlation has previously been reported between atmospheric pollution (acid rain, fog, particulate pollutants, etc.) and pine withering. Using Numazu-city and the surrounding area in Shizuoka Prefecture as a survey site, pine needles were collected from black pine trees along roads experiencing large amounts of traffic and roads with relatively small amounts of traffic. The stomata of these pine needles were then inspected for blockages, and the nature of these blockages was determined. In many cases, pine leaves obtained from high traffic areas appeared abnormal, and the anterior cavities of stomata were blocked by particulate substances containing the carcinogens, dibenz [a, h] anthracene and benzpyrene, among others. As pine trees become enfeebled and weak, these chemicals reduce secretions of the natural insecticides stilbene (pinosylvin etc.) in the duramen. As this would render pine trees to susceptible easy attack from the vector of the pine wood nematode, Bursaphlenchus xylophilus, these particulate pollutants are thought to be one of the causes of the "pine withering" phenomenon.
