Phenological disorder induced by atmospheric nitrogen deposition : Original causes of pine forest decline over Japan. Part II. Relationship among earlier phenological development, extreme of minimum air temperature, and forest decline of pines over the Japan

Abstract

Since the early 1970s, more than 25% of Japanese red pine forests have died or declined in Hiroshima Prefecture, Japan. Mass mortality phenomenon of pine trees has appeared throughout Japan, expanding northward from the Prefectures in southern Japan such as Nagasaki, Kogashima. The mortality was above 80% in Nagasaki, Kumamoto, Miyazaki and Tokyo. This study shows that the massive mortality of pines forest mainly occurred in south-facing slopes, where mortality was 90% in Gokurakujisann Mount, Hiroshima. The mortality was very low, < 3.7%, on north-facing slopes and mountain peaks. On west-facing slopes, the mortality was 20–40%. The foliar phenological development on south-facing slopes was 14 days earlier than that on north-facing slopes, 18 days earlier than that on mountain peaks. The mortality of pine trees in Gokurakujisann Mount increased with earlier phenological development and was significantly correlated (R = 0.98**). The mortality of pine trees in each Prefecture increased from south to north with earlier phenological progress and was significantly correlated (R = 0.56**). The outbreak of pine tree mortality was closely related to appearance of abnormally extreme lowest air temperature in February and March. The annual ring width in Gokurakujisann Mount was decreased from 1972 to 1984, concomitantly the abnormally extreme lowest air temperature in February and March. Based on these, it may be concluded that the combined effects of accelerated phenological progress and reduced frost hardiness caused by acid deposition, mainly nitrogen deposition, and extreme abnormally lowest air temperature in late winter and early spring in February and March are the original main factors of mortality of pine trees on a large scale.