New global database opens the door for better understanding of terrestrial ecosystem productivity

(Press-News.org) With CMCC’s contribution a new study and database provides scientists with an unprecedented resource for understanding how Earth's land systems store carbon and produce biomass, establishing a benchmark for calibrating vegetation models and assessing ecosystem responses to environmental change.

Net primary production (NPP) represents the carbon accumulated by plants through photosynthesis after accounting for their own respiration - essentially the amount of biomass ecosystems produce annually. This fundamental measurement underpins our understanding of global carbon cycling, food production, and climate change impacts on terrestrial systems.

"Net primary production is a fundamental measure of biomass production in ecosystems," explains Balzarolo, who contributed to this study. "It represents the carbon accumulated annually by plants through photosynthesis, corresponding to the remainder of the photosynthetic gain, or gross primary production, after accounting for the autotrophic respiration."

The importance of NPP extends far beyond academic research. As Balzarolo emphasizes, "It's the carbon invested for the annual production of plant biomass and a key service for society by providing foodstuffs, fibres, fuel, and construction material. NPP is also a key variable in the global carbon cycle and resulting impact on the Earth system."

Despite decades of research that have led to the accumulation of large quantities of data, a consistent global NPP database has remained elusive. This gap stems partly from methodological differences that lead to poor data harmonization, but also from a lack of comprehensive synthesis efforts since the International Biological Program of the 1960s-70s. 

More recent databases typically focus on single ecosystem types, rarely accounting for measurement methodology and methodology uncertainty associated with the data added to the database. Crucially, many exclude estimates for belowground production, which represents over 30% of global annual NPP and is expected to be even higher in water-limited ecosystems.

Filling the gaps

The new database addresses these limitations by providing harmonized NPP measurements across six major biome types: forests (206 sites), grasslands (145 sites), croplands (34 sites), northern peatlands (34 sites), tundra (21 sites), and dry shrublands (16 sites). The geographic coverage spans all continents across 50 countries, with measurements extending from 1959 to 2023.

"In situ NPP global databases rarely account for the measurement methodology and thus quality of the data, and often do not include estimates for belowground production," notes Balzarolo. The team's rigorous approach ensures approximately 95% of NPP estimates derive from direct biometric methods.

The database's strength lies in its methodological rigor. A key innovation is the development of a system that provides consistent quality assessments across diverse measurement approaches making it easier to compare or combine results. The research team created site-specific uncertainty estimates accounting for biome-specific variances, method-specific reduction factors, and monitoring time spans.

This uncertainty framework proves particularly valuable when constructing regression models. The researchers demonstrate that accounting for measurement uncertainties when fitting NPP-climate relationships can result in 40% different estimates compared to ignoring data quality variations.

The database can reveal important patterns in terrestrial productivity across climate regions, which enables a comprehensive analysis of how environmental conditions drive productivity patterns across Earth's major terrestrial ecosystems. 

Broader scope

The implications for climate science are profound. Dynamic Global Vegetation Models used in climate projections rely heavily on empirical NPP relationships for construction, calibration, and validation. "The database can be used to study the environmental drivers of NPP, explore patterns in terrestrial NPP, in particular differences in above and belowground production, as well as serve as a benchmark for the calibration and validation of process-based vegetation models and remote-sensing products," explains Balzarolo, who is also Scientific Leader of CONCERTO, a project coordinated by CMCC that aims to revolutionize the way we understand and monitor the global carbon cycle.

The comprehensive dataset, therefore, enables researchers to track ecosystem responses, which is essential as "tracking ecosystem NPP helps scientists and policy makers in monitoring changes in biomass production, sustainable resource management, and modelling plant biomass losses due to climate change, drought, wildfires, or deforestation," notes Balzarolo.

The database represents extensive international collaboration and stems from a long collaboration with Prof. Matteo Campioli and colleagues of the University of Antwerp in Belgium. “The new model for NPP in the CONCERTO project will crucially rely on this database," she says.

“We are particularly satisfied with this publication and database, because it is an important recognition of the work not only of today’s junior researchers, such as the leading author Marie Rodal, but also of the efforts of thousands of experimental scientists who, since the 1970s conducted NPP measurements in the field. Without their work, the database construction would have not been possible, whilst at the same time the database greatly valorizes their old data,” says Matteo Campioli, co-author of the study and researcher at the University of Antwerp. 

By providing standardized, high-quality productivity measurements across Earth's major ecosystems, this database will support more accurate climate projections, enhance ecosystem management strategies, and inform evidence-based environmental policies addressing the global climate crisis.

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