Comparative ecophysiology ofChrysanthemum pacificum Nakai andsolidago altissima L. 1. whyS. altissima cannot be established on the seashore

A fieldsurvey was made to elucidate whether salt spray is a major factor in preventing a common inland weed,Solidago altissima, from being established on the seashore of Boso Peninsula. Seasonal changes in the intensity of salt spray, sodium content in the soil water and soil water contents were measured at the seashore and inland. Seeds ofS. altissima were sown at both sites with those of a common maritime species,Chrysanthemum pacificum. The number of surviving shoots of the seedlings were periodically counted for 1 year. The intensity of the salt spray, sodium content and water contents of the soil on the seashore fluctuated seasonally. There were some periods when the intensity of salt spray was comparable to that of the inland site. Most of theS. altissima seedlings survived at the inland site. AllS. altissima seedlings germinated at the seashore were completely eliminated. The death rate ofS altissima seedlings at the seashore was not constant. Ninety-five percent of theS. altissima seedling in total died out during the four periods of intensive salt spray. The death rate ofC. pacificum seedlings on the seashore was not especially high during those periods. Correlation between seasonal changes in the death rate ofS. altissima seedlings and the sodium content or water content of the soil was low. These results indicate that intensive salt spray, intermittently blown in from the sea, is one of the most critical environmental factors that eliminatesS. altissima from the seashore.