Mortality of planted <Emphasis Type="Italic">Pinus thunbergii</Emphasis> Parlat. saplings subject to coldness during winter and soil types in region of seasonal soil frost

To assess and improve methods for the development of coastal forests in Hokkaido, northern Japan, this study examined the factors affecting mortality of planted Pinus thunbergii Parlat. saplings in a region with seasonal soil frost. The needles of pine saplings at the study site turn red in late spring, suggesting xylem embolism, which can lead to death. Sapling mortality was strongly correlated with the degree of cold just after planting and with the occurrence of repeated severe winters. Volcanic ash soil had been supplied to improve the soil nutrients, and the volcanic ash soil always thawed later than the original coastal sand. Saplings in volcanic ash were significantly more damaged than those in original coastal sand. This suggests that hydraulic stress caused by cuticular transpiration under frozen soil conditions during spring may also accelerate damage due to embolisms. Hence, volcanic ash soil should not be applied to soils in regions with seasonal soil frost. A covering of woodchips can help prevent frost from reaching greater soil depths, and, indeed, fewer saplings at the study site died in areas with such coverage. Planting location can also affect pine sapling mortality. For example, shading caused by wood fencing may affect the soil freezing profile during winter; therefore, planting close to a fence should also be avoided in regions with seasonal soil frost. These findings should be used to improve the development of forests in regions with seasonal soil frost.