Rings of fire: centuries of tree growth show wildfires increasing in Vietnam

火環(huán)：幾個(gè)世紀(jì)的樹木生長(zhǎng)表明越南的野火正在增加

The data suggest human activities are more to blame for the increase than climate change.

數(shù)據(jù)表明人類活動(dòng)比氣候變化更應(yīng)為這一增長(zhǎng)負(fù)責(zé)。

Jude Coleman（作者）

The first centuries-long analysis of wildfires in southeast Asia has been compiled using tree rings from a region in central Vietnam. There has been a drastic increase in the frequency of wildfires in the area over the past 100 years, but climate change is not the primary culprit. Instead, humans lighting fires for agriculture are behind the rising number of forest burns, according to the study1?published in?Geophysical Research Letters.

對(duì)東南亞野火長(zhǎng)達(dá)數(shù)百年的首次分析是利用越南中部地區(qū)的樹木年輪編寫的。在過(guò)去的100年里，這個(gè)地區(qū)的野火頻率急劇增長(zhǎng)，但氣候變化不是罪魁禍?zhǔn)?。相反，根?jù)發(fā)表在《地球物理通訊》上的研究，人類為農(nóng)業(yè)點(diǎn)火是森林燃燒數(shù)量不斷增加的幕后推手。

“Fire has a big impact on the forest structure,” says Thiet Nguyen, a forest ecologist and PhD student at the University of Melbourne in Australia. “There’s a very high level of biodiversity in that forest.”

“火焰對(duì)森林結(jié)構(gòu)有巨大的影響，”澳大利亞墨爾本大學(xué)的森林生態(tài)學(xué)家兼博士生Thiet Nguyen說(shuō)，“那片森林的生物多樣性非常高。”

Many people think of tropical Vietnam as lush with jungle, but in the central highlands, misty montane forests are home to around 100,000 hectares of conifers mixed with broadleaf trees. Whereas tropical trees don’t tend to put on annual growth rings because they grow consistently year-round, the conifers have annual cycles of growth. Nguyen and his colleagues took cross-sections from recently fallen trees of two species,?Pinus kesiya?and?Keteleeria evelyniana, at 12 locations in Bidoup Nui Ba National Park and counted the tree rings back over almost 400 years.

許多人認(rèn)為熱帶的越南叢林茂盛，但在中部高原，霧蒙蒙的山地森林是大約10萬(wàn)公頃針葉樹和闊葉樹的家園。熱帶樹木不會(huì)因?yàn)槿瓿掷m(xù)生長(zhǎng)而形成年輪，而針葉樹則有每年的生長(zhǎng)周期。Nguyen和他的同事們?cè)贐idoup Nui Ba國(guó)家公園的12個(gè)地點(diǎn)拍攝了最近倒下的兩種樹木的橫截面，這兩種樹木分別是卡西亞松和云南油杉，并統(tǒng)計(jì)了近400年前的樹木年輪。

When trees are exposed to non-lethal fires, their bark chars, leaving behind a burn scar within the tree rings. The team dated the earliest definite fire scar to 1772. Between then and 1905, only 17% of years contained clear fire scars, although Nguyen admits that the farther they went back in time, the smaller was the available number of samples, reducing their confidence in the findings. After 1905, they had good clear tree rings to work with. From then until 1963, 71% of years showed scars from fires, however the fires often affected only a small number of sites. But from 1964 to the present day, fire has occurred almost every year, often affecting a larger number of sites.

當(dāng)樹木暴露在非致命的火災(zāi)中時(shí)，它們的樹皮會(huì)燒焦，在樹環(huán)內(nèi)留下燒傷疤痕。研究小組將最早確定的火災(zāi)痕跡定為1772年。從那到1905年，只有17%的年份有明顯的火災(zāi)痕跡，盡管Nguyen承認(rèn)，他們回到的時(shí)間越遠(yuǎn)，可用的樣本數(shù)量就越少，這也降低了他們對(duì)發(fā)現(xiàn)的信心。1905年以后，他們有了很清晰的樹木年輪。從那時(shí)到1963年，71%的年份展現(xiàn)了火災(zāi)的痕跡，然而火災(zāi)總是只影響少數(shù)地點(diǎn)。但是從1964年到今天，火災(zāi)幾乎每年都會(huì)發(fā)生，往往影響到更多的地點(diǎn)。

‘A big problem’

‘一個(gè)大問(wèn)題’

Until the advent of this study, “we had no idea how the fire regime has been changed”, says Nguyen. “If the fires are increasing rapidly, that can reduce biodiversity and forest density,” he adds. “It’s a big problem.”

直到這個(gè)研究出現(xiàn)以前，“我們不知道火災(zāi)體系是如何改變的”，Nguyen說(shuō)，“如果火災(zāi)迅速增長(zhǎng)，可能會(huì)降低生物多樣性和森林密度?！彼a(bǔ)充道，“這是一個(gè)大問(wèn)題?！?/span>

Using statistical analysis, the authors looked for relationships between fires, climate and the human population. They discovered that historically, fire patterns were associated with climate; data from Pacific sea surface temperatures (see 'Forests on Fire') showed that weather patterns such as El Ni?o and La Ni?a, which determine dry or wet years, could have influenced how much combustible plant material was available and how dry and flammable it was, for example.

通過(guò)統(tǒng)計(jì)分析，作者尋找了火災(zāi)、氣候和人口之間的關(guān)系。他們發(fā)現(xiàn)，從歷史上看，火災(zāi)體系與氣候有關(guān)；例如，來(lái)自太平洋海面溫度的數(shù)據(jù)（見(jiàn)“著火的森林”）表明，厄爾尼諾和拉尼娜等決定干旱或潮濕年份的天氣模式可能會(huì)影響可獲得的可燃植物材料的數(shù)量以及其干燥和易燃程度。

But after 1963, according to population estimates for the nearby city, Da Lat, an increasing number of people came to live in the area. Humans use fire to clear land for agriculture, Nguyen says, and fire probably spreads to the national park — established in 2004 — from nearby areas. People also start fires in the park. From 1964, the authors found that the signal from humans overwhelmed climate as the driving force behind the fires.

但1963年后，根據(jù)附近城市達(dá)拉特的人口估計(jì)，越來(lái)越多的人來(lái)到該地區(qū)居住。Nguyen說(shuō)，人類利用火災(zāi)為農(nóng)業(yè)開墾土地，火災(zāi)可能從附近地區(qū)蔓延到2004年建立的國(guó)家公園。人們也在公園里生火。從1964年起，作者發(fā)現(xiàn)人類發(fā)出的信號(hào)超過(guò)了氣候，成為火災(zāi)背后的驅(qū)動(dòng)力。

The fires’ increasing frequency, coupled with heightened fire conditions brought on by climate change, will be a problem in the future, says Brendan Buckley, a dendrochronologist at Columbia University in New York, who was a master’s programme adviser to Nguyen but was not involved in this study. “There might very well be some burning that gets out of control in these areas that are protected rainforest.”

火災(zāi)頻率的增加，加上氣候變化導(dǎo)致的火災(zāi)條件的加劇，將成為未來(lái)的一個(gè)問(wèn)題，Brendan Buckley說(shuō)，他是紐約哥倫比亞大學(xué)的樹木年代學(xué)家，是Nguyen的碩士項(xiàng)目顧問(wèn)，但沒(méi)有參與這項(xiàng)研究?！霸谶@些受保護(hù)的雨林地區(qū)，很可能會(huì)發(fā)生燃燒失控。”

Understanding historical and modern fire occurrence is crucial because it gives researchers a baseline to work from, helping forest managers to prepare for climate change, Buckley says. Although fire can be beneficial to a coniferous forest, the rainforest is a totally different ecosystem and can be destroyed by fire, he says.

Buckley說(shuō)，了解歷史和現(xiàn)代火災(zāi)的發(fā)生至關(guān)重要，因?yàn)檫@為研究人員提供了一個(gè)工作基準(zhǔn)，幫助森林管理者為氣候變化做好準(zhǔn)備。他說(shuō)，盡管火災(zāi)對(duì)針葉林有利，但雨林是一個(gè)完全不同的生態(tài)系統(tǒng)，可能會(huì)被火災(zāi)摧毀。

Nguyen says that the species used in this study are common across other parts of southeast Asia, such as Thailand and the Philippines, meaning that the same technique could be used to explore fire history and climate change in other countries.

Nguyen說(shuō)，這項(xiàng)研究中使用的物種在東南亞其他地區(qū)很常見(jiàn)，如泰國(guó)和菲律賓，這意味著同樣的技術(shù)可以用于探索其他國(guó)家的火災(zāi)歷史和氣候變化。

“If we had this kind of study in other countries in southeast Asia, a big historical fire reconstruction for the region, that would be cool.”

“如果我們?cè)跂|南亞的其他國(guó)家進(jìn)行這種研究，為該地區(qū)進(jìn)行歷史大火的重建，那就太酷了?！?/span>

doi: https://doi.org/10.1038/d41586-023-02235-y

（本文僅用于學(xué)習(xí)英語(yǔ)，并未用于其他用途）