The effect of soil conditions on climate-growth correlations at two Pinus nigra sites

Climate change is modifying precipitation distribution and increasing drought events frequency, leading to decline in many stands. Pinus nigra was introduced to Poland in the 19th century as a measure to mitigate negative effects of soil pollution. This species is also known to be well adapted to drought conditions. However, its response to drought on different soil conditions remains unclear. The aim is to investigate the growth relation of P. nigra to drought and its resilience under the same climatic conditions but different soil types (fertile and poor soils) in central Poland. Two mature stands of P. nigra were selected, one on fertile soil and one on poor soil. Tree-ring data were collected and analysed to assess growth patterns and climate sensitivity. Resilience indices were calculated for seven common drought years, i.e. 1940, 1954, 1963, 1976, 2003, 2006 and 2015, to compare the impact of soil conditions on drought response. The study found similar climate-growth correlations for both soil types, with March temperatures and summer precipitation positively affecting growth, highlighting the significant influence of local climatic conditions on growth. However, resilience to drought varied between poor and fertile soil, with opposite trends observed in the drought year 1976 (characterized by dry June, wet July and dry August) and in the drought years 1963 and 2006 (characterized by wet June and dry July and August). With a higher resilience for the trees on poor soil in 1976 and a higher resilience on fertile soil in 1963 and 2006. Moreover, differences were not consistently observed: only 3 of the 7 years were significantly different. The study indicates that soil conditions partially influence the resilience of P. nigra to drought, but the relationship seems drought episode-dependent. Relationships between soil fertility and climate-growth dependencies are complex, and to draw more robust conclusions, further studies are needed, incorporating additional soil types.