Unraveling the paper jungle of biodiversity and ecosystem services relationships

Policy makers make use of ecosystem services as a focal point for conservation efforts. The relationships between biodiversity and ecosystem services – services ecosystems provide for humans, such as water supply, oxygen production, and carbon sequestration – have been studied for a long time. However, so far some studies on tropical forest ecosystem services show contradictory results. New research by the Copernicus Institute of Sustainable Development may shed some light and consolidate these seemingly conflicting relationships. Though the positive relationship between biodiversity and carbon storage seems to stand true, relationships with other ecosystem services are still largely unclear. Is nature conservation actually achieved when ecosystem services are protected?

Different plant species in the understory of a forest in Surinam
The plant species-rich understorey of a tropical forest in Suriname. Credit: Gijs Steur

"It seemed like every reported relationship had been tested in a different way, for example by using different methods, assumptions, or different definitions for plant biodiversity,” says Gijs Steur, PhD candidate at the Copernicus Institute of Sustainable Development and lead author of the study. “When I started looking into these relationships, I landed in this paper jungle of different results, reports and a seemingly fragmented state of knowledge, and it was very difficult to connect everything into a coherent complete collection.”

Carbon storage supporting biodiversity

Thus, Steur carried out a meta-analysis on this paper jungle. What he and supervisors Pita Verweij, René Verburg and Martin Wassen found is that there is indeed a positive relationship between biodiversity and carbon storage in tropical forests. “We found evidence that forests with a higher amount of woody plant species also contain higher carbon stocks, suggesting that if we protect forests with high amounts of carbon, we also protect a large number of plant species,” Steur explains.

Birds-eye view of the diverse tropical forests of Suriname
Birds-eye view of the diverse tropical forests of Suriname. Credit: Luc Haverhals

Although some studies have reported negative or no relationships between biodiversity and carbon storage, Steur may have found a reason: “The size of the research area seems to influence the relationship you find. Imagine you’re studying relationships between biodiversity and ecosystem services on European islands. If you only look at the Dutch Wadden Islands, you will probably find different relationships than when you also include, say, the Greek Islands,” Steur explains. “You can’t just throw all of that data together and assume that you compare like with like. It might be that the situation on the Wadden Islands is completely different than that on the Greek Islands, although they are all islands.” If you include all islands in a comparison when these differences are large, you could find no relationship or a different relationship than when you would compare them separately.

“This is exactly what was happening in the studies that we reviewed. Those studies that reported a different outcome usually compared tropical forests that were far apart from each other. Until our meta-analysis, we were relatively unaware that differences between tropical forests can cause different outcomes. What we have learned is that when tropical forests lie far apart one need to either study them separately, or take the differences into account in the analysis, to be able to communicate unambiguously to policy makers.”

Three palm nuts that are used to produce edible or medicinal oils. From left to right: amana (Astrocaryum aculeatum), bugrumaka (A. sciophilum), awarra (A. vulgare).
Three palm nuts that are used to produce edible or medicinal oils. From left to right: amana (Astrocaryum aculeatum), bugrumaka (A. sciophilum), awarra (A. vulgare). Credit: Jeffrey Brand

Next on the agenda

Though it is a good sign that Steur found an overwhelming positive relationship between biodiversity and carbon sequestration, that doesn’t mean policy makers can now relax their efforts: biodiversity may not have such a positive relationship with other ecosystem services. Reports on the services of the production of timber and other valuable forest products (non-timber forest products – for example the palm nuts used to make edible and medicinal oils, shown in the photo), which are important services for local forest dwelling communities, were more difficult to draw general conclusions from. “We found hardly any studies that considered relationships of these services with plant diversity.” Whether there are synergies between protecting these two ecosystem services and conserving biodiversity is thus still unclear, and is the next topic on Steur’s PhD research agenda.

Publication: Steur, G., Verburg, R.W., Wassen, M.J., Verweij, P.A., 2020. Shedding light on relationships between plant diversity and tropical forest ecosystem services across spatial scales and plot sizes, Ecosystem Services, Volume 43, 101107, ISSN 2212-0416, https://doi.org/10.1016/j.ecoser.2020.101107.