ALBERT

Description: Tree and tall shrub above ground biomass (AGB) samples were taken in five areas: a treeless mountainous tundra (16-KP-04; Lake Rauchuagytgyn area), tundra-taiga transition zone (16-KP-01, Lake Ilirney area; 18-BIL-00) and a northern taiga (18-BIL-01, 18-BIL-02). In total, 31 sample plots with 15-m radius were investigated for tree and tall shrub AGB. The only present tree species there is Larix cajanderi Mayr. By tall shrubs we mean Pinus pumila (Pall.) Regel, Alnus viridis ssp. fruticosa (Rupr.) Nyman and Salix spp. L. Three living trees (the lowest, a tree with the average height and the highest) per each site were cut down. From each individual tree certain representative samples were taken: samples of branches, needles, cones and tree stem discs. Sampled branches were divided into four categories: 1) big (first order, connected to the stem), 2) medium (second order, connected to the big branches), 3) small (third order, connected to the medium branches), 4) dead (including dead cones). Needles are typically found on the third order branches. Cones were divided by colour (red, brown and grey). Tree stem discs were taken at the base of a tree (0 cm, disc A), breast height (130 cm, disc B) and top/close to the top of a tree (260 cm, disc C). To estimate each tree's stem biomass, the stem was assumed to have a cone shape. Dead trees were also sampled, but irregularly (not at every sample plot). In most cases, they did not have branch and needle material, so the samples of dead trees mostly consist of tree discs' samples. Tall shrubs were representatively sampled similarly to trees – three individuals per site. Samples included branch, leaves/needles and cones/catkin biomass. All harvested AGB samples were weighed fresh in the field and subsampled. All subsamples were oven dried (60 °C, 48 h for shrub and tree branch samples, up to one week for tree stem discs) and weighed again. Protocol for total tree and shrub AGB estimation can be found enclosed as a separate file. All data were collected by scientists from Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research and University of Potsdam, Germany, The Institute for Biological problems of the Cryolithozone, Russian Academy of Sciences, Siberian branch, and The Institute of Natural Sciences, North-Eastern Federal University of Yakutsk, Yakutsk, Russia.” All data were collected during the “Chukotka 2018” expedition, that has been supported by the German Federal Ministry of Education and Research (BMBF), which enabled the Russian-German research programme “Kohlenstoff im Permafrost KoPf” (grant no. 03F0764A) and by the Initiative and Networking Fund of the Helmholtz Association and by the ERC consolidator grant Glacial Legacy of Ulrike Herzschuh (grant no. 772852).