Database led to breakthrough in forest research

Systematic forest data have been collected in Sweden for over 100 years. Every year, the Swedish National Forest Inventory (NFI) gathers data on the state and changes within the country’s forests. This long-standing resource is invaluable for researchers, especially considering the extensive time series of permanent plots that allow for the study of changes over time.

Swedish Leadership in Research

National forest inventories, such as the Swedish NFI, are present in many countries worldwide. The ways in which these data sets are used have evolved over time. A pivotal peer-reviewed study by Swedish ecologists significantly advanced ecological research.

In 2013, the article “Higher levels of multiple ecosystem services are found in forests with more tree species” was published in Nature Communications. In writing the article, the researchers used survey data in an innovative way that was ground breaking at the time.

- That article was a game changer, says Bertil Westerlund, a researcher at SLU Riksskogstaxeringen and the lead on Swedish data deliveries to the Global Forest Biodiversity Initiative (GFBI). It gave us insights into how ‘failing’ to regenerate and manage a forest might result in the natural regeneration of more species. This is exactly what we see happening in Swedish forests.

The article’s impact stemmed partly from the Swedish NFI’s use of permanent sample plots for decades, as well as advances in data technology and modelling. According to Westerlund:

- It was a whole new way of working. We trialled new models, applied them to larger areas, and drew conclusions based on that. This was possible thanks to repeated measurements on permanent plots, which began in 1983. Additionally, significant advances in research methods and data technology enabled us to apply our survey data in new ways.

Merging Data on a Global Scale

Historically, national inventory data like Sweden’s NFI were mainly used for statistical analysis and traditional forest research, but not much for ecological studies. The realization that a global database could aid biodiversity research led to the creation of GFBI.

- This data collection has helped us understand ecological mechanisms across different regions, leading to conclusions we could never have drawn otherwise, says Tom Crowther, one of GFBI’s founders and a professor at the Department of Environmental Systems Science at ETH Zürich.

Crowther and his team initially aimed to conduct a global tree analysis. By reaching out to institutions worldwide for inventory data, they collected information from hundreds of thousands of sample points, eventually publishing a study showing that there are over three trillion trees on Earth. A global analysis of this scale had never been attempted, although national estimates existed.

- After this initial data collection, I was contacted by Jingjing Liang at Purdue University, who had developed a large dataset examining the relationship between biodiversity and carbon sequestration. We combined our datasets and proved that biodiversity plays a key role in increasing carbon sequestration, says Crowther.

The group formalized their efforts as GFBI, and the initiative later expanded to a web-based platform called Science-i.

Swedish Expertise in GFBI

Sweden’s data contributions to GFBI are focused on the permanent sample plots of the Swedish NFI, which account for around 60 percent of the data collected annually and data are updated regularly.

- We’ve provided data, but also expertise, having used survey data for so long and learned how to use it effectively, says Bertil Westerlund. We’ve answered questions on how to compile data for the global database and balance the various data subsets with research objectives.

While only a subset of all the available data is used—such as tree species and biomass growth—it must be harmonized for compatibility across borders.

- Inventory programs don’t use the same sample plot sizes or the same number of sample plots per unit area, so we must balance the data along with sample intensity (the number of plots per hectare). It’s essentially one large harmonization effort, explains Westerlund.

Some of the most influential studies using Swedish NFI data include Climatic controls of decomposition drive the global biogeography of forest-tree symbioses (Nature 2019), The number of tree species on Earth (Proceedings of the National Academy of Sciences, 2022), and Co-limitation towards lower latitudes shapes global forest diversity gradients (Nature Ecology & Evolution, 2022). Numerous other studies have been published based on the same data, with SLU deciding on a case-by-case basis whether to appear as co-authors.

According to Westerlund, GFBI’s global approach offers a distinct advantage: the ability to generalize findings beyond a local or regional scale.

- In forest biology and ecology, research typically evaluates causal relationships at smaller scale, such as the interaction between tree species and soil fungi or the effects of tree diversity on biomass production. What GFBI has enabled us to do is extend these findings to broader global ecosystems, including entire biospheres.

Text: Translation made by AI tool, edited by Anna-Lena Axelsson.