Human activities have led to the widespread die-off of boreal forest in the Russian Arctic, according to a new study published on 25 September in Ecology Letters (1), demonstrating the direct and indirect effects of industrial pollution in the local region and beyond.
In the largest study of its kind to date, the team of international researchers led by the University of Cambridge examined tree rings from Norilsk in the Russian Arctic and east of the Yenisei River. The tree ring dataset was used to reconstruct forest die-off in the Russian region.
Norilsk, one of the worlds northernmost cities, is located within the Arctic circle in northern Siberia and regarded as the most heavily polluted place on Earth. The city was established to accommodate mining activities, however, decades of mining without environmental regulations have led to severe pollution.
In addition, more than 15,000 tonnes of diesel oil have spilt into local rivers. A massive oil spill in May 2020 has added to the extreme level of environmental damage.
In a statement, Prof Ulf Büntgen from Cambridge’s Department of Geography explained: “Using the information stored in thousands of tree rings, we can see the effects of Norilsk’s uncontrolled environmental disaster over the past nine decades”.
“While the problem of sulphur emissions and forest dieback has been successfully addressed in much of Europe, for Siberia, we haven’t been able to see what the impact has been, largely due to a lack of long-term monitoring data.”
The ring width and wood chemistry measurements were combined with soil characteristic studies and computer modelling to assess the environmental damage caused by copper and nickel mining. The scientists discovered that airborne emissions from the Norilsk industrial complex have destroyed around 24,000 square kilometres of boreal forest since the 1960s.
After quickly realising the immense scale of the circulation patterns, the researchers decided to expand their analysis to boreal forests outside Norilsk’s mining complex. They were astonished by the extent of the damage, which has spread up to 100 kilometres.
“Since atmospheric pollution in the Arctic accumulates due to large-scale circulation patterns, we expanded our study far beyond the direct effects of Norilsk’s industrial sector and found that trees across the high northern latitudes are suffering as well.” Büntgen added: “What surprised us is just how widespread the effects of industrial pollution are — the scale of the damage shows just how vulnerable and sensitive the boreal forest is”.
Pollution in the atmosphere reduces trees’ ability to turn sunlight into energy through photosynthesis. Although global warming is expected to increase the rate of boreal tree growth, trees in this region will not grow as quickly or as strong as they would in areas with lower pollution levels. Apart from making forests more vulnerable to disease and death, slower growth also reduces the amount of carbon that can be sequestered.
The scientists suggest that air pollution in the area is partly responsible for the “Arctic dimming” phenomenon, which provides new evidence to explain the so-called divergence problem – the decoupling of tree ring width from rising air temperatures observed since the 1970s.
(1) Kirdyanov, A.V. et al. Ecological and conceptual consequences of Arctic pollution. Ecology Letters (2020). DOI: 10.1111/ele.13611.