気候変動：オーストラリアで高木の枯死が増えている

Tree deaths may have doubled in North Queensland, Australia, between 1984 and 2019, suggests a Nature paper. The findings indicate that tree life expectancy is potentially halving in this region, an effect associated with increased climate change and wind-disturbance events due to cyclones.

Tropical forests are critical to the global carbon cycle and are known to influence the pace of climate change. Previous research suggests that tree death is accelerating in some regions of the tropics, with consequences for the future of the tropical carbon sink, in which carbon dioxide is absorbed from the atmosphere. However, the mechanisms that may be driving tree death, and whether particular species are especially vulnerable, remain unclear.

David Bauman and colleagues analysed patterns of tree death between 1971 and 2019, using 74,135 trees from 81 different species and 24 forest plots in North Queensland. They found that annual tree death risk has, on average, doubled across all plots and species between 1984 and 2019. Trees in drier local climates were found to have a higher average mortality risk. Atmospheric water stress, driven by global warming, may therefore be a primary cause of increasing tree death in moist tropical forests, the authors suggest.

Improved assessments of tree health could advance our ability to assign cause to individual tree deaths, the authors argue.