Decadal changes in masting behaviour of oak trees with rising temperature

Abstract

Decadal changes in masting behaviour—directional changes in seed production with fluctuations on a decadal time-scale—are attracting widespread attention in the context of global climate change. However, our mechanistic understanding of the effects of climate on seed production on a decadal scale is unsatisfactory, partly because of the insufficient statistical analyses of long-term data on masting. We detected decadal changes in masting behaviour in the Japanese oak Quercus crispula based on long-term data (38 years: 1980–2017) from the Kitakami Mountains of Japan. The moving average of seed production in a 20-year sliding window increased, whereas the coefficient of variation decreased. A wavelet power spectrum, as well as a second-order log-linear autoregressive (AR) model showed that masting intervals shortened from 3- or 4-year cycle to a 2-year cycle. The moving average of seed production increased linearly as the moving average of temperature increased. Temporal variations of the two AR model coefficients as a function of temperature were well described by concave curves. Synthesis. By conducting the statistical analyses of a long-term seed production dataset, we obtained significant evidence of decadal changes in the masting behaviour of the Japanese oak and showed that the shortening of the masting interval was associated with rising temperature. A resource allocation shift and an environmental veto were discussed as possible mechanisms underlying the decadal change.