In the realm of forest ecology and climate science, a long-held assumption has guided our understanding of carbon sequestration: that the act of photosynthesis in trees directly correlates with growth, particularly in the production of woody biomass. However, groundbreaking research now challenges this fundamental belief. A recent observational study, conducted across diverse oak tree populations in the United States, reveals a surprising disconnection between photosynthetic activity and actual tree growth. Presented in the esteemed journal Science Advances, the findings suggest that trees, despite maintaining substantial photosynthetic rates late into their growing seasons, halt their physical expansion months earlier than previously thought.
At its core, photosynthesis is the process by which trees assimilate atmospheric carbon dioxide (CO2) and convert it into organic compounds using sunlight. It has been widely accepted that this carbon fixation necessarily translates to tangible increases in trunk diameter, branch thickness, and root volume—the woody structures that represent long-term carbon storage. Yet, the new study’s intensive measurements depict a nuanced reality: photosynthesis continues late into the year; however, the physiological growth of the trees—measured by the expansion of trunk girth—ceases by midsummer in eastern U.S. oaks and stops by August in Californian variants. This decoupling shakes the foundational assumptions of carbon cycle models that factor tree growth as a primary carbon sink.
This finding holds profound implications for climate modeling and forest management. Models currently employed to predict global carbon dynamics often assume a tight coupling between photosynthesis and biomass accumulation. As atmospheric CO2 levels rise due to anthropogenic emissions, these models hypothesize enhanced photosynthetic rates, resulting in accelerated tree growth and greater carbon storage. However, if photosynthesis does not directly lead to increased wood production, the capacity of forests to act as long-term carbon sinks may be substantially overestimated, thereby impacting forecasts of climate change mitigation.
The research team, led by ecoclimatologist Mukund Palat Rao from the Lamont-Doherty Earth Observatory at Columbia Climate School, employed an integrative approach involving satellite-based photosynthesis assessments, in situ CO2 flux monitoring, and precise dendrometric measurements from trunk sensors. These sensors captured minute changes in tree diameter, allowing the team to track real-time growth activity. Their analysis extended over multiple sites across eastern United States and California, leveraging over seven decades of growth ring data and regional temperature records to contextualize observed patterns.
Notably, trees exhibit daily cycles of expansion and contraction, influenced by water uptake and transpiration. The trunks expand during nighttime when roots absorb water, swelling the wood and cells. Conversely, daylight hours induce slight shrinkage due to transpiration-driven water loss. Despite these fluctuations, genuine growth—reflecting cell division and expansion leading to increased woody biomass—occurs only during defined seasonal windows. The data reveal that the crucial growth window for eastern U.S. oaks spans May through July, while in California, it predominantly occurs from December to April, both ceasing well before photosynthetic activity tapers off.
This temporal mismatch becomes particularly apparent during periods of water limitation. Trees require adequate internal water pressure to sustain cell growth; thus, dry, hot conditions promptly halt growth activity. Intriguingly, photosynthesis proves more resilient, continuing at moderate levels despite reduced soil moisture, albeit at a slightly diminished rate. This physiological decoupling may be attributed to the distinct cellular processes governing carbon fixation versus cell expansion and biomass formation, highlighting an intricate regulatory mechanism in plant metabolism.
The carbon absorbed during these late photosynthetic phases appears to be allocated towards non-structural functions. Instead of contributing to woody tissue, it supports the synthesis of foliage and root structures or feeds metabolic pathways that maintain cell viability through dormancy phases. Some of this carbon serves as starch reserves that enable rapid bud and shoot growth in subsequent seasons. Beyond the tree itself, a portion of this assimilated carbon is released into the rhizosphere, where it sustains microbial communities essential for nutrient cycling and pathogen defense.
Quantifying the exact fraction of carbon locked into long-lived woody biomass remains challenging. Current evidence suggests that a significant share is diverted into short-term physiological roles rather than permanent sequestration. This revelation necessitates reevaluation of carbon budget models that rely heavily on tree growth as a proxy for forest carbon storage capacity—particularly under future climate scenarios marked by increased CO2 concentrations and extreme weather variability.
Moreover, the research highlights that in years characterized by erratic local climate—oscillating between drought and precipitation extremes—the disconnect between photosynthesis and growth intensifies. Such fluctuations are anticipated to become more frequent in a warming world, potentially exacerbating the divergence between carbon uptake and wood production. This insight signals an urgent need to refine predictive models to incorporate the complex interactions of hydrological stress, phenological shifts, and metabolic allocation.
Future research directions are already underway, spearheaded by Rao and collaborators, seeking to determine whether this decoupling phenomenon extends beyond oak species to other tree taxa and ecosystems globally. Preliminary expectations suggest variance across forest types and climatic zones, potentially influenced by species-specific physiology and environmental constraints. Clearly, this line of inquiry opens a new frontier in understanding forest carbon dynamics, with critical repercussions for managing natural carbon reservoirs amid accelerating climate change.
In summary, this study reveals that photosynthesis and tree growth, long assumed synonymous, are mechanistically independent under certain conditions. This paradigm challenges existing climate models and urges the scientific community to rethink estimates of forest carbon sequestration. As forests remain a cornerstone of global carbon management strategies, deeper insights into these physiological processes are indispensable to accurate forecasting and effective climate policy development. The discovery underscores the complexity inherent in ecological systems and the ongoing need for integrative, high-resolution research methodologies.
Subject of Research: Not applicable
Article Title: New Research Indicates That in the Future, Trees May Store Less Carbon Than Expected
News Publication Date: 12-Jun-2026
Web References: http://dx.doi.org/10.1126/sciadv.ady7139
References: Palat Rao, M., et al. “New Research Indicates That in the Future, Trees May Store Less Carbon Than Expected.” Science Advances, 12 June 2026.
Image Credits: Not specified
Keywords: Carbon cycle, Biogeochemistry, Biogeochemical cycles, Dendrochronology, Photosynthesis, Plant physiology, Plant respiration, Climate change
