The data of tree-ring widths and stable carbon and nitrogen isotopes of mature Qinghai spruce in the central Qilian Mountains

The data of tree-ring widths and stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes of mature Qinghai spruce (<i>Picea crassifolia</i>) in the central Qilian Mountains, northwest China, from 1840 through 2019.中国西北祁连山中部成熟青海云杉（Picea crassifolia）的树木年轮宽度、稳定碳同位素（δ¹³C）及氮同位素（δ¹⁵N）数据，时间跨度为1840年至2019年。