Carbon sequestration by ecosystems is disrupted in major regions of the world

A study led by researchers from the University of Antwerp and CREAF, the Catalan Research Center for Ecology and Forest Management, shows that vast natural areas around the world are showing signs of instability and are therefore on the brink of radical change. In doing so, the ability of these areas to sequester carbon may be affected.

A study published this week in the prestigious journal Nature points to clear signs of disruption of carbon sequestration in terrestrial ecosystems across large parts of the world. According to the study, the Mediterranean region, Southeast Asia and the West Coast of North and Central America are the most vulnerable areas for instability. In the Mediterranean, sudden changes can turn forests into thickets of undergrowth.

The difference between CO2 absorption and emission in these regions fluctuates more and more, with some years of strong vegetation growth (and therefore high carbon sequestration) and other years of weak vegetation growth (and low carbon sequestration). The authors of the study warn that this increasing variability indicates environmental perturbation, resulting in abrupt changes.

Forests become thickets

“Not only is the variability of these ecosystems increasing, but their ‘memory’ is also increasing, where the increase in carbon in a given year is increasingly related to the increase in the previous year. For example, lower carbon uptake is likely to be followed by an even lower increase in the following year,” says lead author of the study, University of Antwerp and CREAF. Researcher Marcos Fernandez.

“These are clear signs of the destabilization of key ecosystems, which can cause sudden changes in landscapes. For example, in Mediterranean ecosystems, forests may turn into thickets with undergrowth, a process that is irreversible in the current climate.

The study confirms that regions at risk of instability have less forest cover and more cropland, are hotter and experience greater temperature fluctuations. This may be associated with an increase in extreme weather conditions such as heat and cold waves. These risk areas include the West Coast of North and Central America, the Mediterranean, East Africa, India, Pakistan, and Southeast Asia.

For this study, the research team worked with global net ecosystem production data for the period 1981-2018 from two global atmospheric inversion models, CAMS and CarboScope. They also used data on net ecosystem production from TRENDY, a suite of twelve dynamic global vegetation models.

Instability makes carbon sequestration difficult

The study shows that the ability to sequester carbon has been compromised in recent years in regions at risk of destabilization, while that capacity has actually increased in areas where variability has decreased, such as the Amazon and parts of central and northern Europe. “Although carbon was lost in the Amazon during the study period, the losses are becoming smaller as the carbon sequestration capacity of these systems increases,” explains CREAF researcher Joseph Penuelas.

“Predicting the carbon cycle is essential if we want to fight climate change, because terrestrial ecosystems currently capture a third of human carbon emissions. If these areas’ ability to sequester carbon declines, we will all have to limit our CO2 emissions even more,” says one of the study’s authors, Sarah Wicka (UAntwerp). ).

“We don’t yet know whether such sudden changes will change the climate or the ability of plants to sequester carbon, but either way, the potential destabilization of large areas of the biosphere makes it very difficult to make predictions.”