Wind and topography influence the crown growth of Picea jezoensis in a subalpine forest on Mt. Deogyu, Korea

Tree growth in subalpine ecosystems is sensitive to wind due to their wide exposure to strong winds and sparsely wooded short surroundings. This study was conducted to understand the effects of wind and topographic wind barriers on the tree growth in a subalpine ecosystem. The annual shoot growth, bud mortality and needle moisture content of Jezo spruce (Picea jezoensis (Siebold et Zucc.) Carrière) were compared between a wind-exposed site and a wind-protected site. The wind-exposed site was located in a windward position and was exposed directly to the prevailing winds from W and WSW. The wind-protected site was located on leeward slopes with topographic barriers that blocked the prevailing winds. The wind-exposed site had higher air temperature, lower soil water content and shallower snow depth than the wind-protected site in late winter and spring. The annual mean shoot growth on the wind-exposed site was 4 cm – significantly lower than that of 6.1 cm on the wind-protected site (P < 0.01). The bud mortality was highest at 32.9% in the western sectors of the upper crowns in the wind-exposed site, which was the crown sector that was most exposed to the prevailing winds. The needle moisture content decreased by 8–60% from January 2009 to April 2009, and the decrease was significantly higher in the wind-exposed site than in the wind-protected site (P < 0.01), indicating the potential for drought stress in trees in the wind-exposed site. Topographic wind barriers play a decisive role on the tree growth in subalpine areas by changing temperature and moisture regimes, lowering needle moisture loss and bud mortality, and reducing the potential for drought stress.