Forests with numerous tree species, and therefore a mix of water-management strategies, appear more tolerant of drought.

在森林里种植多样树种，并因此使用混合的水管理策略，这样能使森林更耐干旱。

撰文播音：克里斯托弗·因塔利亚塔（Christopher Intagliata）

翻译：陈美娟

审校：郭晓

You've probably heard the financial advice that a diversified portfolio is better in turbulent times? Well that same wisdom may hold true for our stocks of trees. Because ecologists say forests with a diversity of trees are better at weathering drought. The reason: 

你可能听说过这样的理财建议：在动荡时期，多元投资组合是更好的选择。这种智慧同样适用于树木储备。因为生态学家说，树种多元的森林能够更好地抵御干旱。原因是：

"There's a huge difference and a huge diversity of water transport strategies in trees." William Anderegg is an ecologist at the University of Utah. "It's everything from having deeper roots or shallower roots, to having these pipes that are incredibly well armored to withstand drought or incredibly weak in the face of drought."

“不同树种运输水分的策略天差地别。”犹他大学的生态学家威廉·安德艾格如是说。“有的树根深植、有的扎根表面，有的全副武装以抵抗干旱、有的则在干旱面前不堪一击。”

Anderegg and his team studied droughts in 40 forests around the world. And the forests with diverse tree populations, with a mix of water-management strategies, did better than forests made up of just one or a few species. Could be a couple reasons for that.

安德艾格和他的团队研究了全球40片森林里的干旱现象。拥有多树种和不同水分管理策略的森林，比那些单一树种或者少树种的森林能更好地应对（干旱）。这可能有两个原因。

"One is that there are other forces that are acting on the ecosystem at the same time. Other stressors like insect attack, or other things they're competing for, competing for light and for nutrients, and this is why a more diverse forest is going to be more functional. It'll be more resilient to drought but maybe also have higher carbon uptake rates over the long term." 

“其中一个原因是，在干旱时，生态系统中有其他外因同时发挥作用。其它刺激源包括昆虫攻击或者树木竞争的光照、营养等，这就是为什么树种多元的森林功能性更强的原因。这样的森林干旱过后的复原性更高，但同时长期的碳吸收率也可能更高。”

The second possibility, he says, is that a monoculture of drought-ready trees may look really resilient to drought. "Up until the drought is severe enough that a whole bunch of the trees shut down or even die. That threshold cliff response you would get in a one species forest and you may not get in a diverse forest." The full report is in the journal Nature. [William R. L. Anderegg et al., Hydraulic diversity of forests regulates ecosystem resilience during drought]

他说，第二个可能的原因是，单一栽培耐旱树种，森林在旱后可能复原力很强。“但干旱要是严重到让一片树木停止生长或者死亡，这种强复原力也就到头了。这种单树种阈值悬崖反应或许不会出现在树种多元的森林中。”完整的研究报告发表在《自然》杂志上。

The lesson for land managers, he says, is that forest restoration efforts following wildfires and disease outbreaks might want to focus on planting a diverse portfolio of tree species. So that even if water plummets, tree stocks will, hopefully, remain stable.

他说，土地管理者可从中得到的经验是，在森林野火和树木疾病爆发之后的森林重建工作应当注重多树种组合的种植。这样即使水资源骤减，树木量也许还有希望维持稳定。