Climate-driven decline of Norway spruce in Central Europe: a threshold crossing in the warming Carpathian Basin.

Norway spruce (Picea abies (L.) Karst.) is an ecologically and economically important conifer species that naturally dominates European boreal forests, the subalpine regions of the Alps, and the Carpathians. It is also widely planted beyond its native distribution area. In 2023, a significant spruce dieback was detected in the Carpathian Basin. To assess the extent of the damage, self-reported data were collected from citizens across Hungary about street, garden, and park spruce trees, covering all counties. A total of 4,081 spruce trees were reported in 2023, of which 2,422 (59.1%) died or showed signs of disease, particularly in areas where summer temperature anomalies exceeded 1 °C. We found a significant positive association (Spearman/Kendall correlation) between mortality rate and mean summer temperatures in previous years, and a negative association with the sum of annual precipitation. The increased spruce mortality in 2023 represents an intensification of a long-term trend that has also been affecting planted spruce forests for decades. The mean annual temperature in the Carpathian Basin seems to be approaching a threshold that exceeds the climatic tolerance of the species. Outside its natural range, the potential shift of areas suitable for planting this species may serve as an indicator of climate change, with ecological shifts progressing faster than previously anticipated. Environmental changes are already visible in the Carpathian Basin, underscoring that continental basins are at heightened risk of climate change. The Norway spruce dieback serves as an example, demonstrating the ecological and economic impacts of species loss due to climate change. Until a global solution is reached, local actions, supported by regional and precise climate models, will be crucial.