Permafrost

Dendroclimatic investigations of forests on permafrost, Central Yakutia,
North-Eastern Russia
A.N. Nikolaev
(Melnikov Permafrost Institute SB RAS, Yakutsk, Russia)
Abstract: The Republic of Sakha (Yakutia) occupies a huge area in north-eastern Russia
situated within the permafrost zone. The region has a sharply continental climate. The response
of dominant tree species to large seasonal temperature variations, from extremely low
temperatures in winter (up to -70°C) to high temperatures in summer (up to 30°C), is of
considerable interest. Climate is known to be a primary control on the distribution of forest
types, as well as on growth and dynamics of woody vegetation. Trees record the evidence of
climatic change in the varying widths of their annual rings.
In the permafrost zone, larch and pine, the dominant forest species, require different
ecological and soil hydrothermal conditions. Larch is more tolerant to cryogenic processes and
grows on the major portion of Yakutia. This is because its root system is normally within 50 cm
depth from the surface. Pine is less tolerant to permafrost conditions. It occupies dry soils with
deep seasonal thawing.
The correlation analysis of tree-ring chronologies from larch and pine growing in different
forest types has revealed relationships between tree growth and soil hydrothermal regime in the
forest type. Tree-ring growth has been found to be significantly correlated with mean monthly
soil temperatures.
The correlation analysis of tree-ring chronologies developed from larch from the
Spasskaya Pad site shows the best correlation with soil temperature conditions at different
depths in the winter season. The higher is the soil temperature, the faster is soil warming, which
promotes timely onset of active tree growth in the beginning of the growing season. Summer
temperatures impose no limitations on radial tree growth. There is a sufficient amount of heat
for rapid tree growth during this period.
The response function of pine growth indicates that it is positively correlated with winter
soil temperatures (until late May) at the upper and lower boundaries of the active layer at depths
of 20 cm and 120 cm. In the depth interval 40-80 cm, the positive effect of temperature is
observed during the spring months. It leads to early thawing of soil and causes growth
processes to begin. In contrast to larch, however, a considerable negative effect of summer
temperatures on pine growth is observed at some depths. This may be explained by significant
moisture deficit in drier soils where warm temperatures have a desiccating effect.
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