Habitat-specific responses of shoot growth and distribution of alpine dwarf-pine (Pinus pumila) to climate variation

Alpine dwarf-pine (Pinus pumila) in dominant in the alpine regions of Japan, and often forms the krummholz zone of stunted alpine forest. The distribution of P. pumila is strongly related to the distribution of snow, and shoot growth is also sensitive to weather conditions. Changes in temperature and snowmelt regimes may well affect the distribution patterns of the krummholz zone. P. pumila usually occupies the habitat between the fellfield and snowbed communities, and responses to climate change may differ depending on whether plants are close to the fellfield or the snowbed. We compared the distribution and shoot growth patterns of P. pumila close to both surrounding ecosystems in the Taisetsu Mountains, northern Japan. P. pumila has expanded its distribution area by 14 % toward both edges over the last 32 years. Annual shoot growth was positively affected by summer temperature and sunshine duration, but negatively related to spring temperature toward the fellfield side. Shoot growth was greater at the southeastern edge of patches, where snowdrifts were formed. The results indicated that shoot growth and distribution area increased in warm summers. However, warm springs might have a negative influence on shoot growth, probably because the earlier reduction in cold-resistance enhances the risk of frost damage in spring close to the fellfield side. This study suggests the importance of understanding the site-specific responses of shrubs to predict the impacts of climate change on alpine ecosystems.