Department of Geography and Environmental Systems, University of Maryland Baltimore County, Baltimore, MD, USA.
Glob Chang Biol. 2020 Sep;26(9):4679-4690. doi: 10.1111/gcb.15187. Epub 2020 Jul 2.
Two recent global maps of tree restoration potential have identified vast regions where tree cover could be increased, ranging from 0.9 to 2.3 billion hectares. Both maps, however, emphasized dryland regions, with arid biomes making up 36%-42% of potential restoration area. Dryland biomes have repeatedly been recognized as inappropriate regions for expanding tree cover due to the risks of biodiversity loss, water overconsumption, and fire, so maps that highlight these regions for restoration must sustain careful scrutiny. Here, I show that both recent attempts to map restoration potential in arid regions have been hindered by underlying errors in the global tree cover maps they used. Systematic underestimates of existing sparse tree cover led directly to large overestimates of the potential for tree recovery in drylands. The Atlas of Forest Landscape Restoration Opportunities (Laestadius et al., Unasylva, 2011, 62, 47) overestimated tree restoration potential across a third of arid biomes by between 7% and 20% (55-166 million hectares [Mha]). Similarly, Bastin, Finegold, Garcia, Mollicone, et al. (Science, 2019, 365, 76) overestimated tree restoration potential across all arid biomes by 33%-45% (316-440 Mha). These inaccuracies limit the utility of this research for policy decisions in drylands and overstate the potential for tree planting to address climate change. Given this long-standing but underappreciated challenge in mapping global tree cover, I propose various ways forward that keep this lesson in mind. To better monitor and restore tree cover, I call for re-interpretation and correction of existing global maps, and for a new focus on quantifying sparse tree cover in drylands and other systems.
两份最近的全球树木恢复潜力图确定了大片可以增加树木覆盖的区域，范围从 0.9 亿到 23 亿公顷不等。然而，这两份地图都强调了旱地地区，干旱生物群系占潜在恢复面积的 36%-42%。由于生物多样性丧失、水资源过度消耗和火灾的风险，旱地生物群系一再被认为是不适宜扩大树木覆盖的区域，因此强调这些区域进行恢复的地图必须受到仔细审查。在这里，我表明，最近两次试图绘制旱地恢复潜力的尝试都受到了它们所使用的全球树木覆盖地图中潜在错误的阻碍。对现有稀疏树木覆盖的系统低估直接导致对旱地树木恢复潜力的巨大高估。《森林景观恢复机会图集》（Laestadius 等人，《联合国粮农组织林业通讯》，2011 年，62 卷，47 页）对旱地三分之一以上的生物群系的树木恢复潜力高估了 7%到 20%（5500 万到 1660 万公顷[Mha]）。同样，Bastin、Finegold、Garcia、Mollicone 等人（《科学》，2019 年，365 卷，76 页）对所有旱地生物群系的树木恢复潜力高估了 33%-45%（3160 万到 4400 万公顷）。这些不准确之处限制了这项研究在旱地政策决策中的实用性，并夸大了植树造林应对气候变化的潜力。鉴于在绘制全球树木覆盖地图方面存在这一长期但未被充分认识的挑战，我提出了一些前进的方法，牢记这一教训。为了更好地监测和恢复树木覆盖，我呼吁重新解释和纠正现有的全球地图，并将重点放在量化旱地和其他系统中稀疏树木覆盖上。
