Studies on theAbies population of Mt. Shimagare

Abstract

The survivorship curve is estimated for theAbies population of the subalpine wave-regenerated forest on Mt. Shimagare in the northern Yatsugatake Mountains, Central Japan. The repetition of decay and regeneration of nearly even-aged stands is the nature of this forest in a steady-state, so that the survivorship curve is given as the decrease of density with stand age. Four distinct stages are recognized on the curve. The mortality is high in the first 10 years (stage i). Though germination is observed from the floor under dense canopy to the forest edge, only a portion of the seedlings can survive and form a nearly even-aged young regeneration. The established regeneration enjoys a low mortality before it attains a full density state (stage ii, until 32 years). When full density is reached, as indicated by the −3/2 power law, the mortality increases again due to an intensive self-thinning (stage iii). However, mortality rate declines with age. This decline is thought to occur because canopy trees become uniform in size and spatial distribution. In the last stage the aggregative dying-off of trees takes place (stage iv, about 90 years). The uniformity among trees is believed to promote the collapse of the stand.