Effects of Strong Wind and Ozone on Localized Tree Decline in the Tanzawa Mountains of Japan

Abstract

The numerical simulation of wind and ozone (O3) transport in mountainous regions was performed with a computational fluid dynamics technique. A dry deposition model for O3 was designed to estimate O3 deposition in complex terrain, and the qualitative validity of the predicted O3 concentration field was confirmed by comparison with observed data collected with passive samplers. The simulation revealed that wind velocity increases around ridge lines and peaks of mountains. The areas with strong wind corresponded well with the sites of tree decline at high altitudes, suggesting that it is an important factor in the localization of tree/forest decline. On the other hand, there is no direct relationship between forest decline and O3 concentration. The O3 concentration, however, tends to increase as wind velocity becomes higher, thus the O3 concentration itself may be a potential secondary factor in the localized decline phenomena. While the diffusion flux of O3 is not related to localized tree decline, the pattern of advection flux is related to those of high wind velocity and localized tree decline. These results suggest that strong wind with large advection flux of O3 may play a key role in the promotion of tree/forest decline at high mountain ridges and peaks.

Keywords

• tree decline
• strong wind
• ozone
• deposition model
• computational fluid dynamics