Growth characteristics of Sakhalin spruce (Picea glehnii) planted on the northern Japanese hillsides exposed to strong winds

Sakhalin spruce (Picea glehnii), a native species typically found in northern Japan, has been used in reforestation on hillsides exposed to strong winds. In the reforestation areas, there are south-facing (S-slope) and northwest-facing slopes (NW-slope). Climatic conditions are contrasting between the two slopes, with shallower snow cover on the S-slopes. We compared growth responses of the spruce to micro-environment between the S- and NW-slopes through soil nutrients, needle longevity, water status, photosynthesis, and nutrients in the needles. These parameters were measured in needles exposed above the snow in winter and in lower needles protected by snow cover. High-position needles suffered from drought stress, especially in winter, and needles were shed early in the year on both slopes. Low-position needles did not suffer from drought stress, and maintained a high photosynthetic rate on both slopes. However, needle longevity was reduced on the S-slope, and concentrations of nitrogen, phosphorus, and potassium in the needles decreased with needle age. Soil nutrient concentrations were low on the S-slope, which suggests that the needles on the S-slope may remobilize nutrients from aged needles to younger needles prior to shedding. This characteristic is probably an adaptation in Sakhalin spruce to poor soil conditions.