Test of the temperature difference model predicting masting behavior

The differential temperature (Delta T) model, based on the assumption that masting plants respond to the difference in the temperatures during the growing seasons 1 and 2 years prior to seed production, has recently been proposed to explain the proximate factor of masting. In this study, we used a 28-year series of data on pollen cone and seed production in Cryptomeria japonica D. Don in Japan and compared several models based on temperatures and resources to test whether Delta T acts as a cue or is a proxy for resource limitation. Of all the models tested, models including Delta T, previous summer absolute temperature Tn-1, and reproduction in the previous year provided the best fit. The number of pollen cones and seeds produced was proportional to the difference in the mean daily maximum temperature during June to August between the preceding two years. In addition, to test whether the double mast events in consecutive years was less common than consecutive warm summers, we used our dataset and 12 datasets of pollen dispersal of 17 years or longer of C. japonica in Japan. Although consecutive warm summers occurred in 4.4% of pairs, double mast events occurred in 1.0%. The Delta T model was a considerably better predictor of the rare phenomenon of double mast events, which occur only after a specific sequence of cold-moderate-hot absolute summer temperatures. Thus, Delta T acts as cue for masting in C. japonica.