Contrasting climate signals across a Scots pine (Pinus sylvestris L.) tree-ring network in the Middle Volga (European Russia)

Since the late-19th century, the Middle Volga has played a major role in the supplying grains and other agricultural products to European Russia. The study area is located in the south of sub-boreal forest in the north and in the forest-steppe in the south. Due to large seasonal differences in rainfall, agriculture in the region, especially in its southern part, strongly depends on hydroclimate variability. According to climate model forecasts, the frequency and intensity of droughts in the Middle Volga are expected to increase due to ongoing warming. Here we introduce 16 new Scots pine tree ring width (TRW) chronologies (Pinus sylvestris L.) from the region and use a dendroclimatological approach to determine what climatic factors drive radial growth. Our analysis revealed contrasting climate signals across the network of sites with chronologies from the north showing weak correlation with May temperature and precipitation (r = ?0.27 and r = 0.28, respectively), while the southern sites demonstrated stronger relationships with climate in the first half of the vegetation season (May to July temperature, r = ?0.26 to ?0.43; May and July precipitation, r = 0.29–0.35). The northern sites did not demonstrate a strong growth response to the self-calibrated Palmer drought severity index (scPDSI) whereas the southern group was more drought sensitive had a strong drought response and positively correlates with scPDSI for the period from previous July to the current October (r = 0.27–0.56). Based on this strong relationship between southern TRW and scPDSI we reconstruct June-September scPDSI using the most sensitive sites (T04S, T06S, T08S) for the period from 1830 to 2014. The model explains 31% of variance. Our reconstruction shows droughts in 19th century: in 1831–33, 1851, 1853, 1859, 1863–65, 1880, 1891–92, 1897–98 and in 20–21th centuries: in 1906, 1921, 1936, 1939, 1967, 1975, 1996, 2010.