地球上的森林覆蓋是多了,還是少了？

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.

盡管人們普遍認為地球上的樹木正在逐漸消失，但發(fā)表在《自然》雜志上的一項研究發(fā)現(xiàn)，地球上樹木的總比例實際上在35年內增加了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.

研究人員通過收集和分析衛(wèi)星圖像來確定這一點，以監(jiān)測高大植被的變化，如樹木，短植被和裸地。 1982年至2016年間，樹木比1982年以前覆蓋了更多的地球，大約864,869平方英里(224萬平方公里)，約為德克薩斯州的三倍。他們的作品于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.

雖然這是一個層面上的好消息 - 更多樹木! - 在其他方面這是個壞消息。雖然森林覆蓋面積可能有所增加，但在同一時期，我們已經失去了大量的熱帶森林覆蓋。整體增長抵消了損失，但這仍然是來自關鍵環(huán)境領域的損失。

"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."

馬里蘭大學地理科學教授、這項研究的合著者馬特·漢森在一份聲明中說：“重要的是要明白，我們正在收獲的樹木并不在雨林中。”當我們看到熱帶以外的高海拔地區(qū)的森林覆蓋增加同時，熱帶森林砍伐仍在繼續(xù)，由此產生的有害碳排放也在繼續(xù)。”

This is where climate change comes in

這就是氣候變化發(fā)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.

高海拔地區(qū)的樹木覆蓋也表明了氣候變化導致的地球溫度變化。在北極周圍的地區(qū)，如西伯利亞東北部、阿拉斯加西部和魁北克北部，氣候變暖使得木本植物在以前沒有的地方生長。

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.

最近的科學證實了這個概念。在2019年5月的一份報告中，研究地球上最北端樹種Dahurian落葉松的研究人員發(fā)現(xiàn)，2005年至2014年，中國北方森林的耐寒樹木比過去40年增長得更多。他們懷疑溫暖的土壤溫度正在助長這棵樹的繁榮，進入永久凍土層，并使樹根——尤其是數(shù)百年樹根——有更多的活動空間。

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.

與此同時，馬里蘭的研究人員通過觀察高分辨率衛(wèi)星圖像并使用概率抽樣，估計35年期間約60%的土地變化與人類活動直接相關，而剩下的40%則是由氣候變化等間接因素造成的。

"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."

漢森說：“這項研究的結果反映了人類主導的地球系統(tǒng)。”從農業(yè)的集約化和擴大到森林和城市土地利用的增加，每一大洲都有人類對景觀的直接作用，這對全球生態(tài)系統(tǒng)服務的維護具有重要意義。”