Tree decline at the somma of Lake Mashu in Northern Japan

Abstract

Decline of the mountain birch (Betula ermanii) has been observed at the somma of Lake Mashu in northern Japan. To clarify its causes, ozone (O3) and fog chemistry were evaluated. O3 concentration was lower in summer, but higher in spring, with a monthly mean of 50-60 ppbv. The results of on-site open-top-chamber (OTC ) experiments using birch seedlings suggested the possibility that O3 decreased the leaf photosynthetic capacity and shifted biomass allocation to the roots. The results of fog measurements showed that the fog acidity was not serious; however, nitrogen input via fog deposition was estimated to be 30 meq m-2 in the plant-growing season, and this could be the main nitrogen source for trees in this area. These results indicated that anthropogenic air pollutants have influenced plant growth in this area. However, there is still great uncertainty about O3 effects on the mountain birch, such as its effects causing stomatal sluggishness, water stresses, and these effects combined with nitrogen input. Further evaluation of these factors is necessary to assess the tree decline.