Does permafrost matter? Permafrost related studies of conifer tree-ring growth in northern Siberia

The world’s largest terrestrial biome, Boreal forest, is prone to the greatest rates of recent and predicted warming. Much of this circumpolar vegetation belt is underlain by permafrost, which further challenges our understanding of the direct and indirect consequences of increasing temperature on the functioning and productivity of these northern latitudinal forests.

Here, we present the results of an on-going study of tree-ring growth of conifers in Russia’s continuous permafrost zone in northern Siberia, from 61-72°N and 90-148°E. Tree-ring data from a variety of habitats between 20 and 600 m asl with different climate and thermo-hydrological regimes of soils are analyzed. While in some cases up to 60-70% of the year-to-year tree-ring width and maximum latewood density variability can be explained by summer temperature variations alone, we find that the seasonal dynamics of permafrost also plays an important role in defining the overall rate of radial tree growth. Wider rings are generally formed on sites with a deeper active soil layer, which itself depends on the geographical location of a site, as well as its ground vegetation, stand parameters and fire history. Waterlogged permafrost may further act as a source of water for trees under exceptionally dry summer seasons.

Our study indicates that the growth response of conifers to temperature and precipitation across the continuous permafrost zone of Siberia is both, site- and species-specific. This implies a range of possible scenarios of further development of northern forests under projected climate change. Seasonal dynamics of the active soil layer and possible permafrost degradation must be taken into account when modelling tree growth variability and forest productivity.