Conifer forest dominates the northern slopes of the mountains in southern Siberian while the southern slopes are mostly covered by steppe vegetation and hemiboreal forest.

"We found that if the warming observed during the 1990–2014 time frame continues for the next couple of decades, the forest belts on the southern slopes in Siberia will recede upslope and, depending on the height of the mountain, may disappear from the south-facing slopes altogether," Ksenia Brazhnik of the University of Virginia, US, told environmentalresearchweb. "Conversely, on the north-facing slopes, we discovered that the mid-slope productivity increases, species ranges shift, and the lower elevation forests experience decreased growth."

These findings are important, said Brazhnik, because if steppe completely dominates the south-facing slopes there will be increased fire activity, which will inhibit regeneration of forest.

Brazhnik, together with Herman Shugart from the University of Virginia, US, predicted that even with a 2°C increase in annual average temperature, biome shifts from forest to steppe will occur in a large area in southern Siberia. These shifts could lead to significant changes in the biodiversity, carbon storage and ecosystem services provided by these forests in the near future.

"Our study helps us understand the time frame over which the changes in forest functionality and ecosystem services are likely to occur," said Brazhnik. "We are no longer talking about what will happen by the year 2100, as significant changes in forest extent and composition are likely to occur in the next several decades."

To perform their calculations, the researchers developed and applied a new 3D forest simulation model called SIBBORK. The model can keep track of the establishment, growth and mortality of millions of trees across tens of hectares of simulated terrain. It considers the heterogeneous response of vegetation to simple environmental changes, such as temperature, precipitation, and light availability, across the landscape.

Although the model does not, at this point, include environmental factors such as permafrost, winds and seed dispersal, or disturbances such as wildfire and insect outbreaks, the vegetation structure and composition it simulates match previous field observations from southern, middle, and northern taiga in central Siberia. This study extends predictions made by other modelling work for this region, with improved spatial and temporal resolution.

Now the researchers are developing disturbance modules for SIBBORK to investigate how fragmentation by forest fires and logging alters forest composition and functionality, in conjunction with climate change. "Disturbances play an important role in shaping the forest," said Brazhnik. "As the boreal ecosystem faces natural and anthropogenic stressors, the health, structure and composition of the forest will depend on the climate, dominating disturbance regimes, as well as the sizes of the remaining forest fragments."

Brazhnik and Shugart reported their findings in Environmental Research Letters (ERL).

Related links

Related stories