Weather conditions favouring cone initiation for Siberian stone pine (Pinus sibirica Du Tour)

Seed production in 25 trees of Siberian stone pine (age 180–200 years) over a 28-year period was examined to determine how the weather factors and their period influence strobilus initiation. Since floral induction in Siberian stone pine occurs in a short period of time only during three weeks at the end of summer, the dynamics of temperature and precipitation during the thirty-days interval, starting from 20 July, were analysed in the present work. The average monthly temperature in July and August, as well as the amount of precipitation in July and August had a weak influence on the number of the cone initiation. There was also a weak influence of weather parameters calculated for shorter time intervals by ten-day interval. Air temperature in the first and second ten-day intervals of July had a weak positive effect on cone initiation, but from the third ten-day interval of this month and throughout August, excessive heat began to negatively affect cone initiation. The only significant negative correlation was found for the temperature of the first ten-day interval of August. This indicates increased sensitivity of initiating cone primordia to air temperature and exactly in this time interval. The example of Siberian cedar pine shows that cool weather during the initiation of macrostrobils favours their abundance. Optimal conditions for cone initiation in Siberian pine are average daily temperatures not higher than +17.5 °C in the first ten-day interval of August. The results of the study expand the understanding of the mechanisms of climatic regulation of generative morphogenesis and are important not only for understanding the fundamental basis of the fruiting process, but also for yield forecasting and management.