Forest fires threaten wipeout for Siberia conifers as deciduous trees take over – In 2015, 2.6 million hectares of forest burned in Russia

Desdemona Despair

24 February 2016 (Siberian Times) – Global warming spells doom for boreal forests with potentially dramatic implications for carbon release in dark taiga.

Climate change is behind a rise in forest fires which are having a direct impact on the tree balance in Siberia, according to a new international study. This shows that conifers are failing to re-establish after these giant and destructive blazes.

Instead deciduous trees are growing in their place, says the author of the study Susanne Tautenhahn, at the Max Planck Institute of Biochemistry in Jena, who worked with a team that included scientists from Krasnoyarsk in Siberia. ‘Boreal forests are one of the largest stores of carbon on Earth, and two-thirds of these forests are located in Siberia,’ said Tautenhahn.

“Fire acts as an important regulator in the natural development cycle of forests – yet climate change is intensifying the frequency and strength of fires, for instance due to lightning strikes, and the natural regeneration processes are being thrown out of balance”.

The investigation has homed in on burned areas along the Yenesei River in Siberia. They have worked out a model for the regeneration of the forest. Seeds of conifers are being outpaced by deciduous which carry much further by the wind. 

The reduction of typical Siberian conifers, which hold high levels of moisture at ground level, increases the likelihood forest fires even further – part of a vicious circle. 

“This can become a self-reinforcing process that could effectively change the eco-system and pave the way for the dominance of deciduous trees on a long-term basis in Siberia,” she said. […]

According to the Federal Forestry Agency, in 2015 there were 11,800 forest fires in Russia covering 2.6 million hectares. In Siberia – 6,900 forest fires rampaged through 2.5 million hectares. [more]

Forest fires threaten wipeout for Siberian conifers as deciduous trees take over

ABSTRACT: Fire is a primary driver of boreal forest dynamics. Intensifying fire regimes due to climate change may cause a shift in boreal forest composition towards reduced dominance of conifers and greater abundance of deciduous hardwoods, with potential biogeochemical and biophysical feedbacks to regional and global climate. This shift has already been observed in some North American boreal forests and has been attributed to changes in site conditions. However, it is unknown if the mechanisms controlling fire-induced changes in deciduous hardwood cover are similar among different boreal forests, which differ in the ecological traits of the dominant tree species.

To better understand the consequences of intensifying fire regimes in boreal forests, we studied post-fire regeneration in five burns in the Central Siberian dark taiga, a vast but poorly studied boreal region. We combined field measurements, dendrochronological analysis, and seed-source maps derived from high-resolution satellite images to quantify the importance of site conditions (e.g., organic layer depth) versus seed availability in shaping post-fire regeneration. We show that dispersal limitation of evergreen conifers was the main factor determining post- fire regeneration composition and density. Site conditions had significant but weaker effects.

We used information on post-fire regeneration to develop a classification scheme for successional pathways, representing the dominance of deciduous hardwoods vs. evergreen conifers at different successional stages. We estimated the spatial distribution of different successional pathways under alternative fire regime scenarios. Under intensified fire regimes, dispersal limitation of evergreen conifers is predicted to become more severe, primarily due to reduced abundance of surviving seed sources within burned areas. Increased dispersal limitation of evergreen conifers, in turn, is predicted to increase the prevalence of successional pathways dominated by deciduous hardwoods. The likely fire-induced shift towards greater deciduous hardwood cover may affect climate-vegetation feedbacks via surface albedo, Bowen ratio, and carbon cycling.

Dispersal limitation drives successional pathways in Central Siberian forests under current and intensified fire regimes