The impact of weather conditions on the development of female cones of Scots pine (Pinus sylvestris L.)

Due to global climate change, the average annual temperature and growing season length have increased in the Northern hemisphere in recent years. In this respect, research of potential changes in seed crop of forest-forming species has become a major problem. Scots pine (Pinus sylvestris L.) is one of the main forest-forming species in the Northern hemisphere. The aim of this work was to study the weather effect in 2006-2012 on the seed cone biometric parameters and seed productivity of Scots pine middle-aged forest stands in mixed coniferous-broad leaved forests (Bryansk region). During the five-year period (2009-2013) about 4 thousands female cones, initiated in 2006-2010, were collected and analyzed. The period of 2006-2012 was characterized by an increase by 12.3% (+1,6°C) in average air temperature from May to October and in the reduction of rainfall by 8.7%, compared to 1961-1990 normal. Through this period in 2010 and 2012 were severe droughts; furthermore, heat wave of 2010 was the strongest during the past 60 yrs. The minimum values of biometric parameters of female cones were observed in the crop of 2012, but not in 2010, as one could expect: 2012<2010 <2009 <2008 <2011. Differences between maximum and minimum values of biometric parameters were (p < 0.01): length - 15.5%; diameter - 14.3%; form factor - 8.4%; weight - 43.2%; number of scales - 17.7%; number of seed scales - 21.6%. Ranking of parameters of seed productivity: 2012<2010 <2008 <2009 <2011 revealed similar trend to cone's biometric parameters. However, ranges of variability between the minimum and maximum values were significantly higher (p < 0,001): mortality of unfertilized ovules - 44.7%; mortality of fertilized ovules - 283.8%; number of plump seeds - 221.5%; weight per 1000 plump seeds - 32.5%; seed efficiency - 201.5% and the number of empty seeds - 165.6%. Strong growth inhibition of female cones in 2012 was associated with intense saturation deficit due to the reduction of rainfall in antecedent off-season and droughty weather in May and June 2012. In contrast, the best development of cones in 2011, contributed to the accumulation of a sufficient amount of precipitation in snowpack and warm humid weather during the growing season in 2011. Synchronous increase in mortalities of unfertilized and fertilized ovules in the crop of 2012, together with minimal crop of cones was associated with abnormal climatological conditions of summer 2010. We showed the futility of using biometric parameters for forecasting of seed productivity due to the high variability of correlation rate for each year. We found out that the cones weight and the weight per 1000 plump seeds are dependable indicators of climatic factors impact in the final year of maturation of Scots pine cones.

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