Stand structure and recent climate change constrain stand basal area change in European forests: a comparison across boreal, temperate, and Mediterranean biomes

Abstract

European forests have a prominent role in the global carbon cycle and an increase in carbon storage has been consistently reported during the twentieth century. Any further increase in forest carbon storage, however, could be hampered by increases in aridity and extreme climatic events. Here, we use forest inventory data to identify the relative importance of stand structure (stand basal area and mean d.b.h.), mean climate (water availability), and recent climate change (temperature and precipitation anomalies) on forest basal area change during the late twentieth century in three major European biomes. Using linear mixed-effects models we observed that stand structure, mean climate, and recent climatic change strongly interact to modulate basal area change. Although we observed a net increment in stand basal area during the late twentieth century, we found the highest basal area increments in forests with medium stand basal areas and small to medium-sized trees. Stand basal area increases correlated positively with water availability and were enhanced in warmer areas. Recent climatic warming caused an increase in stand basal area, but this increase was offset by water availability. Based on recent trends in basal area change, we conclude that the potential rate of aboveground carbon accumulation in European forests strongly depends on both stand structure and concomitant climate warming, adding weight to suggestions that European carbon stocks may saturate in the near future.