Overview

• An analysis of 188 permanent plots monitored for up to about 30 years finds mean tree diameter in intact Amazon forests rose roughly 3.2–3.3% per decade.
• The Nature Plants study, led by RAINFOR scientists, reports a structural shift toward more large trees and fewer small ones across the basin.
• Authors say the pattern is consistent with a fertilization effect from rising atmospheric CO2, with both large and smaller trees increasing in size.
• Large trees, though a small fraction of individuals, account for about half of carbon cycling and storage, making their protection especially consequential.
• The gains are limited to undisturbed forests as fragmentation, fires, and new clearing linked to roads and agriculture threaten to turn more areas into carbon sources, and scientists warn it is unclear whether the trend will persist under intensifying drought and heat.