The boreal forest biome represents one of the most important terrestrial carbon stores, which gave reason to intensive research on carbon stock densities. However, such an analysis does not yet exist for the southernmost Eurosiberian boreal forests in Inner Asia. Most of these forests are located in the Mongolian forest-steppe, which is largely dominated by Larix sibirica. We quantified the carbon stock density and total carbon pool of Mongolia's boreal forests and adjacent grasslands and draw conclusions on possible future change. Mean aboveground carbon stock density in the interior of L. sibirica forests was 66 Mg C ha(-1) , which is in the upper range of values reported from boreal forests and probably due to the comparably long growing season. The density of soil organic carbon (SOC, 108 Mg C ha(-1) ) and total belowground carbon density (149 Mg C ha(-1) ) are at the lower end of the range known from boreal forests, which might be the result of higher soil temperatures and a thinner permafrost layer than in the central and northern boreal forest belt. Land use effects are especially relevant at forest edges, where mean carbon stock density was 188 Mg C ha(-1) , compared with 215 Mg C ha(-1) in the forest interior. Carbon stock density in grasslands was 144 Mg C ha(-1) . Analysis of satellite imagery of the highly fragmented forest area in the forest-steppe zone showed that Mongolia's total boreal forest area is currently 73 818 km(2) , and 22% of this area refers to forest edges (defined as the first 30 m from the edge). The total forest carbon pool of Mongolia was estimated at ~ 1.5-1.7 Pg C, a value which is likely to decrease in future with increasing deforestation and fire frequency, and global warming.

Key message Hydraulic conductivity and wood anatomical traits in Larix sibirica are correlated with macroclimate, and growing season precipitation in particular, along a precipitation gradient of 700 mm year 21 . Abstract Empirical (K s ) and theoretical (K p ) sapwood area-specific hydraulic conductivity, hydraulically weighted (d h ) and simple (d) tracheid diameters as well as tracheid density (TD) in roots, stems, and branches were studied in Larix sibirica trees, the dominant conifer at the southern, drought-affected range limit of the boreal forest in Inner Asia. We compared the hydraulic architecture of L. sibirica in two stands in Mongolia to larch trees grown in Central Europe under moist conditions and related hydraulics to macroclimate (precipitation, temperature) and productivity (basal area increment, BAI). K s , K p , d h , and d correlated positively, and TD negatively with precipitation, temperature, and also BAI. Mean growing season precipitation (MGSP) seemed to affect the hydraulic traits more than temperature. A meta-analysis covering data of 14 conifer species from the northern hemisphere revealed a general relationship between MGSP and hydraulic traits. In contrast to expectation, K p and d h did not show a steady decline from roots through the stem to branches in L. sibirica, but were of similar size or larger in the stem. Our results suggest that considerable plasticity in the hydraulic architecture is an important element of the drought adaptation of L. sibirica. It combines with drought-induced fine root abscission (as reported from earlier work) which may help to protect larger roots and the stem from cavitation.

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