Modelling the Masting Behaviour of Betula platyphylla var. japonica using the Resource Budget Model

Abstract

A masting model of Betula platyphylla var. japonica, a major wind-pollinated tree in Hokkaido, northern Japan, was constructed from the perspective of the resource budget model. An 11-year data series of pollen dispersal by birch showed marked annual fluctuations in flowering. Although flowering fluctuated widely among years, a reciprocal relationship was observed between two consecutive years; very little flowering occurred after a mast year. This suggests that there is a negative relationship between current fruiting and flower bud induction. There was a significant positive relationship in flowering between regions, which suggests that weather conditions regulate flowering in birch. A model that included weather variables and resource allocation systems among years explained 94·5% of the observed annual fluctuations in flowering. In the model, warm spring conditions from bud burst to flower bud development and little flowering in the previous year (t−1) resulted in increased flowering in the current year (t), whereas abundant flowering in year t−2 resulted in a decrease in flowering in the current year (t). The latter indicates that flowering in year t−2 affects resource storage after overwintering; the balance is carried forward to year t−1 and affects the initiation of flower primordia before bud burst. In the model, fluctuating weather conditions in the previous spring strongly affected the masting behaviour of birch.