Abstract: By the methods of wood analysis and sequential soil core, the biomass and productivity of the tree layers in 20-year old Fraxiuns mandshurica and Larix gmelinii plantations, as well as the carbon (C) and nitrogen (N) storages in the above- and below-ground organs of the stands, were estimated. The biomass of F. mandshurica and L. gmelinii was 681510 g·m-2 and 929595 g·m-2, in which, stem occupied 5732% and 5801%, and fine roots occupied 267% and 180%, respectively. The annual productivity of F. mandshurica and L. gmelinii was 161816 and 210245 g·m-2·a-1, in which, stem accounted for 3934% and 4670%, and fine roots accounted for 1206% and 525%, respectively. The C content in the organs of F. mandshurica was lower than that of L. gmelinii, while the N content was in adverse. The C storage of F. mandshurica was lower than that of L. gmelinii, while the N storage had no significant difference between the two tree species. The biomass, productivity, and C and N storages of aboveground organs were lower for F. mandshurica than for L. gmelinii, indicating the higher construction efficiency of the aboveground part of L. gmelinii. Due to the significant differences in the C and N contents between tree species and between the organs of same tree species, the measurement should be made on different tree species and different organs to have an accurate estimation of forest C and N storages.

Key words: Fraxinus mandshurica, Larix gmelinii, productivity, carbon storage, carbon allocation, Qinghai-Tibet Plateau, degraded alpine meadow, scale.