地球上的森林覆盖是多了,还是少了？

Despite the prevailing notion that Earth is losing all its trees, a study published in Nature found that the overall percentage of trees on the planet has actually increased over a 35-year period by 7 percent.

尽管人们普遍认为地球上的树木正在逐渐消失，但发表在《自然》杂志上的一项研究发现，地球上树木的总比例实际上在35年内增加了7%。

 

Researchers determined this by collecting and analyzed satellite images to monitor the changes in both tall vegetation, like trees, short vegetation and bare ground. Between 1982 and 2016, trees grew to cover more of the Earth than before 1982, some 864,869 square miles (2.24 million square kilometers), or about three times the size of Texas. Their work was published in August 2018.

研究人员通过收集和分析卫星图像来确定这一点，以监测高大植被的变化，如树木，短植被和裸地。 1982年至2016年间，树木比1982年以前覆盖了更多的地球，大约864,869平方英里(224万平方公里)，约为德克萨斯州的三倍。他们的作品于2018年8月出版。

While is this is good news on one level — more trees! — it's bad news in other ways. While the amount of tree cover may have increased, we have lost a significant amount of tropical tree cover over that same period. The overall growth offsets the loss, but it's still a loss from a key environmental area.

虽然这是一个层面上的好消息 - 更多树木! - 在其他方面这是个坏消息。虽然森林覆盖面积可能有所增加，但在同一时期，我们已经失去了大量的热带森林覆盖。整体增长抵消了损失，但这仍然是来自关键环境领域的损失。

"It's important to understand that the trees we're gaining are not in rainforests" said Matt Hansen, a University of Maryland professor of geographical sciences and a co-author of the study, said in a statement. "While we saw an increase in tree cover in higher altitudes outside of the tropics, tropical deforestation continues and so do the harmful carbon emissions that result from it."

马里兰大学地理科学教授、这项研究的合著者马特·汉森在一份声明中说：“重要的是要明白，我们正在收获的树木并不在雨林中。”当我们看到热带以外的高海拔地区的森林覆盖增加同时，热带森林砍伐仍在继续，由此产生的有害碳排放也在继续。”

This is where climate change comes in

这就是气候变化发生的原因

That tree cover in higher altitudes also indicates changes in Earth's temperatures because of climate change. Warming in areas around the Arctic, like northeastern Siberia, western Alaska and northern Quebec, allowed for wood vegetation to grow where it previously hadn't.

高海拔地区的树木覆盖也表明了气候变化导致的地球温度变化。在北极周围的地区，如西伯利亚东北部、阿拉斯加西部和魁北克北部，气候变暖使得木本植物在以前没有的地方生长。

More recent science backs up this concept. In a May 2019 report, researchers studying the Dahurian larch, the northernmost tree species on Earth, found the hardy trees grew more in China's northern forests from 2005 to 2014 than in the preceding 40 years. They suspect warmer soil temperatures are fueling this tree boom, eating into the permafrost layer and allowing tree roots — especially the roots of trees that are hundreds of years old — more room to roam.

最近的科学证实了这个概念。在2019年5月的一份报告中，研究地球上最北端树种Dahurian落叶松的研究人员发现，2005年至2014年，中国北方森林的耐寒树木比过去40年增长得更多。他们怀疑温暖的土壤温度正在助长这棵树的繁荣，进入永久冻土层，并使树根——尤其是数百年树根——有更多的活动空间。

Meanwhile, the Maryland researchers, looking at high-resolution satellite images and using probability sampling, estimate that some 60 percent of land change over the 35-year period was connected directly to human activity while the remaining 40 percent was caused by indirect agents, like climate change.

与此同时，马里兰的研究人员通过观察高分辨率卫星图像并使用概率抽样，估计35年期间约60%的土地变化与人类活动直接相关，而剩下的40%则是由气候变化等间接因素造成的。

"The results of this study reflect a human-dominated Earth system," Hansen said. "Direct human action on landscapes is found over large areas on every continent, from intensification and extensification of agriculture to increases in forestry and urban land uses, with implications for the maintenance of ecosystem services worldwide."

汉森说：“这项研究的结果反映了人类主导的地球系统。”从农业的集约化和扩大到森林和城市土地利用的增加，每一大洲都有人类对景观的直接作用，这对全球生态系统服务的维护具有重要意义。”