The data set consists of tree ring width chronologies from tree species. The samples were taken with an increment borer predominantly from the north of the tree at breast height (1.3 m above ground) and were dried in the field. In Potsdam, we sanded, digitized and further processed the scans by identifying the ring layers (from bark to pith and including or estimating the centre) and exporting the tree ring width for each year in one data file. By crossdating we checked against other tree ring width chronologies from the same site for missing rings and corrected them. The data containing files in dendrochronological TUCSON format (1/1000 mm) are added in the Metadata-section as "other version". The region covered is part of the Northern Boreal Forest and the Tundra-Taiga Ecotone (TTE). The fieldwork was planned and carried out by researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). It took place in the peak summer of 2022, from 10 July to 19 August. The study area covers a long bio-climatic gradient from the northern tundra and open forested areas around Inuvik, Northwest Territories, Canada, through the southern Yukon Territory and mountainous terrain across the Mackenzie Mountains and southern Cassiar Mountains, to areas near Fort Nelson, British Columbia, Canada.