Many of us are used to picturing tree growth as a straight line: in summer a tree actively photosynthesizes, processes carbon dioxide, and immediately thickens its trunk and branches. Simple and logical. But for decades scientists were puzzled by a strange paradox: in one year a tree may intensively absorb carbon yet barely thicken, while in another year the growth of its annual rings turns out excellent even though photosynthesis was surprisingly weak.
Because of this mismatch, it seemed obvious that forest growth is limited by internal factors — the respiration needs of plants or the available carbohydrate reserves — rather than by the amount of carbon assimilated. But a new study published in the journal Nature Plants in 2026 under the leadership of Ngoc Nguyen, Miao Zhang and Trevor Keenan refutes this logic.
The authors conducted a large-scale analysis, combining three types of data: observations from carbon flux towers of the FLUXNET and AmeriFlux networks, measurements of tree-ring width, and global vegetation models. Covering 31 forest plots and analyzing data for the period from 1951 to 2020, the scientists discovered something unexpected: short-term fluctuations and mismatches do not affect the long-term picture. Over 70 years, wood mass grew strictly in proportion to photosynthesis. In other words, trees may temporarily put carbon "in storage" because of uneven uptake, but on the scale of decades they remain a reliable filter for carbon dioxide.
Imagine a river flowing into a lake. The water level in the lake rises in proportion to the volume of inflow, even if the water moves unevenly because of rapids and the zigzags of the riverbed. So it is with trees: their annual rings record not every fluctuation of photosynthesis but the net carbon balance accumulated over the year. This finding has important consequences for climate models. To correctly assess the role of forests in combating global warming, one must rely not on short-term measurements but on long, multi-year observations. Only they reveal the true capacity of forests to accumulate carbon and serve as a climate stabilizer.
