Unveiling China’s natural and planted forest spatial-temporal dynamics from 1990 to 2020

Tree planting has been suggested as a potentially effective solution for mitigating climate change. China has implemented the world’s largest afforestation and reforestation project since the 1970s, but high-resolution maps of China’s planted forests remain unavailable. In this study, we explored the use of multi-source remote sensing images and crowdsourced samples to produce the first high-resolution (30-m) map of China’s planted forests. We constructed a Google Earth Engine (GEE)-based mapping framework using spectral, temporal, structural, textural and topographic features derived from multi-source remote sensing data. Combined with over 600,000 field samples, we generated wall-to-wall planted forest maps at 30-m resolution for China every-five years from 1990 to 2020. Our maps were compared with planted forest map of National Forest Inventory and the reported National Forestry Statistical Yearbook, showing minor differences in the area and significantly positive relationships (R2 ranged from 0.8 to 0.9, P < 0.01). The overall accuracies for the generated quinquennial maps ranged from 77.3% to 81.8% from 1990 to 2020. Quinquennial maps of China’s planted forest from 1990 to 2020 reveal that the area of planted forests expanded at an annual rate of 14,613 km2, representing a 94.33% net increase from 464,715 km2 in 1990 to 903,099 km2 by 2020. This increase in planted forest area was the combined result of a gain of 479,681 km2 and a loss of 41,297 km2, leading to a net increase of 438,384 km2.
Natural forest label as 2；Planted forest label as 33.

植树造林被认为是缓解气候变化的潜在有效手段。自20世纪70年代以来，中国实施了全球规模最大的造林与再造林工程，但目前仍缺乏中国人工林的高分辨率分布图。本研究探索利用多源遥感影像与众包样本，生成了首幅中国人工林高分辨率（30米）分布图。我们基于谷歌地球引擎（Google Earth Engine, GEE）构建了制图框架，提取了多源遥感数据的光谱、时间、结构、纹理与地形特征。结合逾60万个野外实测样本，我们生成了1990年至2020年间每5年一期、分辨率为30米的全覆盖中国人工林分布图。将本研究生成的人工林分布图与国家森林清查人工林图及公开的《中国林业统计年鉴》数据进行对比，结果显示两者在面积上差异较小，且呈现显著正相关关系（决定系数R²介于0.8至0.9之间，P < 0.01）。1990年至2020年间生成的各期五年期人工林分布图总体精度介于77.3%至81.8%之间。1990年至2020年的中国人工林五年期分布图显示，人工林面积以每年14613平方公里的速率扩张，相较于1990年的464715平方公里，至2020年时累计净增长94.33%，总面积达903099平方公里。人工林面积的增长源于新增面积479681平方公里与减少面积41297平方公里的共同作用，最终实现净增438384平方公里。天然林标注为2；人工林标注为33。