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.

QcSeedfall.txt

This file is raw data in Appendix S4. It contains 8 columns; site name, date when the contents of the seed traps were collected, trap ID, species name, number of mature seeds and comments. However, from 1980 to 1986 and in 1998, the total number of mature seeds in all collection days for each trap was shown. In 1992, the total number of mature seeds in all collection days and trap was shown.

QcSeedWt.txt

This file is raw data in Appendix S1_Fig. S5. It contains 5 columns; Seed ID, monitoring year, trap ID, weight of a seed (g) and comments. However, from 1987 to 1994 and in 2007, the seed trap ID is unknown.

weatherYabu.txt

This file is data in Appendix S1_Fig. S6, and contains 11 columns; monitoring year, mean temperature (°C) from 20-May to 10-June, mean temperature in June, July, August and September, and total rainfall (mm) in each period. Those data were downloaded from the web site of the Japan Meteorological Agency (https://www.data.jma.go.jp/gmd/risk/obsdl/index.php).