Some observations of phenology and ecophysiology ofDaphne kamtschatica Maxim.var.jezoensis (Maxim.) Ohwi, a shade deciduous shrub, in the forest of northern Japan

Abstract

The phenology and leaf traits ofDaphne kamtschatica Maxim. var.jezoensis (Maxim.) Ohwi, the only summer deciduous shrub (20–40 cm) in the temperate forest of northern Japan, are examined. This plant carries through the winter mature leaves and well formed flower buds. It flowers in early spring during snowmelt and begins photosynthesis under relatively high irradiance under an open forest canopy. Our results show that there is significant carbon gain during the period when new leaves and fruit maturation also take place. Beginning in June, as the forest canopy closes, leaves onDaphne shoots senesce acropetally and the plants become completely bare in mid-July. After a period of 20-day dormancy, the shoots begin to resprout. Leaves become mature in early October and remain on the stem over winter. Leaf traits and photosynthesis measurements suggest as follows. 1) By becoming summer deciduous,D. kamtschatica avoids the cost of maintaining leaves inefficient under deep shade. 2) The onset and breaking of the summer dormancy is triggered by photoperiod since plants at the forest edge also become dormant even when light remained relatively high. However, the decreased duration of dormancy with higher light levels suggests that there is a tendency towards shorter dormancy where summer shade is absent and this could eventually lead to an evergreen habit such as that found in the alpine speciesDaphne miyabeana.