Decadal changes in masting behaviour of oak trees with rising temperature

1. 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 insufficient statistical analyses of long-term data on masting.

2. 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 years to a 2-year cycle.

3. 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.

4. Synthesis. By conducting 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 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.