Forests slow their growth for up to four years after severe drought, a period during which they are less able to act as carbon sinks, a new study reports. The study's results suggest that current Earth system models should incorporate the impact of drought on forests in order to provide more accurate predictions of how drought will alter the global carbon cycle.

Researchers have suggested that climate change could lead to more frequent and/or intense climate extremes, including more severe drought. However, the impacts of climate extremes on forests, while critical for predicting climate-altering carbon cycle changes, are poorly understood. Models that try to capture these impacts typically assume that vegetation recovers quickly and completely from extreme drought, which some scientists have questioned.

Here, William Anderegg and colleagues examined the recovery of tree stem growth after severe drought at 1,338 forest sites around the world, comparing their observations to simulated results of tree stem recovery from various climate-vegetation models.

In the observed data, the researchers found regularly reduced growth for one to four years after severe drought across many taxonomic groups and a broad geographic range, and particularly in dry ecosystems. By contrast, the models they studied showed minimal effects from drought in the same regions, suggesting these tools may need to be reevaluated so that drought impacts are accurately captured.