Pyrogenic Carbon Pools of the Upper Amur Region

Study relevance. Russian forests have the largest pool of carbon C among terrestrial ecosystems, and they are subject to periodic fires. Combustion products remain in soils for thousands of years and are now the longest term pool of carbon. However, the size of this pool in soils is still not understood very well in terms of knowledge about the C reserve structure in Russian forests. Study objectives. Our objectives are to determine the content and structure of pools of total and highly stable forms of pyrogenic carbon (PyC), estimate the proportions of various PyC forms within the soil C, and study the relationship between the PyC and the stand characteristics and soil properties of periodically burning larch forests of the Upper Amur region. Study objects and methods. This paper presents data from the first field assessment of the total and highly stable forms of pyrogenic C pools in the soils of regularly burning larch forests of the Upper Amur region along a 500-km transect from north to south. Total and stable forms of pyrogenic carbon have been studied; the reserves and thickness of litter, as well as soil density, moisture, pH, and content of Corg and N, have been determined. Study results. In the upper soil layer, the total concentration of PyC varies from 1 to 2.2%, and the stock reaches 3.3 t/ha. The proportion of total PyC in the soil organic C pool reaches 21%, while the proportion of highly resistant PyC forms does not exceed 4%. A principal component analysis revealed that the concentration and stock of total PyC in soils do not depend on soil properties, but tend to increase towards the north. At the same time, the content and reserves of highly stable PyC, which mirrored the high-intensity fires, positively and significantly correlate with the proportion of larch in the forest stand. Conclusions. Our results indicate the predominance of low-intensity surface fires, which do not result in the formation of a large number of highly stable forms of PyC. The fire strength is likely to correlate positively with the larch regeneration.