Does summer warming reduce black spruce productivity in interior Alaska?

High-latitude warming has had a discernible effect on the productivity of boreal forests. Here, we report a change in the growth responses of a major biome of boreal North America, black spruce, to climatic warming, based on tree rings sampled at 11 sites in interior Alaska. Tree ring growth was negatively correlated with growing season air temperature, but positively correlated with annual precipitation. The magnitude of the negative correlation increased with increasing growing season temperature until the 1980s, suggesting that warming-induced drought restricted the productivity. However, after the mid-1990s, the negative correlation diminished, and tree ring growth responded positively to air temperature, suggesting that the productivity of the high-latitude forest, and potentially its carbon uptake, will increase under expected warming. The future trajectories of high-latitude forests in interior Alaska and associated carbon cycle feedback will depend on the duration and strength of this renewed response under future climatic warming.