Shoot dynamics of Pinus pumila in relation to altitudinal and wind exposure gradients on the Kiso mountain range, central Japan

Seasonal shoot dynamics of Japanese mountain stone pine (Pinus pumila Regel.) growing at six sites with different altitudes and slope aspects on the Kiso mountain range in central Japan were investigated. The shoots followed a similar growth pattern at all sites; current shoots elongated rapidly during June and July, and the current needles grew during July and August. Final lengths of the current shoots and needles decreased with increasing altitude. Current-shoot lengths were also shorter at the windward sites than at the leeward sites. At all sites, leaf senescence occurred intensively between mid-August and mid-September. Needle longevity, i.e., the age of the oldest living needle attached to a shoot, increased with increasing altitude. Fascicle density, i.e., the number of current needle fascicles on a unit shoot length, was greater at higher altitudes and windward sites than at lower altitudes and leeward sites. Seasonal dynamics of the P. pumila shoots were characterized by simultaneous replacement of old needles with new needles in the early autumn, thus avoiding any loss of canopy photosynthetic production during the growing season. Increases in needle longevity and fascicle density were associated with declining air temperature and increasing wind exposure. Needle longevity and fascicle density were characteristics of adaptive plasticity in P. pumila that prevent a reduction in growth potential in the stressful conditions of alpine regions.