Growth response of Pinus sylvestris L. and Picea abies [L.] H. Karst to climate conditions across a latitudinal gradient in Sweden

Pinus sylvestris L. (Scots pine) and Picea abies [L.] H. Karst. (Norway spruce) are the most important economic tree species in Sweden. However, like every other tree species, they are affected by climate change, especially drought conditions. In this study, we analysed the effect of climate variability on the radial growth of Scots pine and Norway spruce in Sweden. Sixteen sites of pairwise monospecific stands of Scots pine and Norway spruce distributed across latitudinal gradients in Sweden (55 – 67 ° N) were used. In each site, we sampled at least 15 dominant/codominant Scots pine and Norway spruce trees without any defect in the sampled plots’ buffer zone (3 – 5 m wide). We performed a correlation analysis between climate variables and the radial growth of the species using different timescales; and regressed the coefficients with latitudes. Thereafter, important climate variables for both species were identified. Our results showed that temperature is the main climate factor affecting the radial growth of Scots pine while Norway spruce is more sensitive to early summer precipitation. The impact of summer precipitation on the radial growth of both species transitioned from a positive to a negative trend across a latitudinal gradient. Conversely, a contrasting pattern was noted in the relationship with summer temperature. The radial growth of both species responded positively to spring temperature, particularly at lower latitudes. The resistance of pine and spruce to drought showed a clear linear increase with latitude (p < 0.001). Compared to spruce, pine showed a better capacity to attain pre-drought growth levels (i.e., resilience) and was independent of latitude. Our findings contribute to the understanding of the spatial patterns of the growth-climate relationship of Scots pine and Norway spruce in Sweden; and could offer useful guidance on adaptive forest management in the face of climate change.