树木是具有木质树干及树枝的植物，可存活多年，人们一般将乔木称作为树。树的分枝距离地面较高，可形成树冠。树木在减少土地侵蚀及气候调节方面具备相当重要的作用，树叶可以从空气中吸收二氧化碳，并将大量的碳储存在自身组织内，从而缓解“热岛效应”。

镰刀菌 (Fusarium) 是一类世界性分布的真菌，它常常会侵染植物，引发植物的根腐、茎腐、花腐和穗腐等多种病害。镰刀菌通常会侵染寄主植物维管束系统，破坏植物的输导组织维管束，并在植物的生长发育代谢过程中产生毒素危害植物，造成其萎蔫死亡，影响其产量和品质。

本篇课程首发于2017年6月5日

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Trees Save Lives

Dead trees mean dead people, and scientists are finally starting to figure out why. It's only been in the past few years that anyone has been willing to go out on a limb and associate morbidity and mortality numbers with nature. Oh, sure, everyone agrees that trees pull particulate-matter pollution out of city air. Simply by dint of being shady, trees reduce the "urban heat island" effect that drives people to run their AC all the time, a contributor to climate change. And, yes, trees inhale carbon dioxide, another win for the climate.

A 2015 meta-analysis of the few studies that had tried to take up the issue showed that higher exposures to green space, even while considering things like poverty and education level, indeed resulted in a statistically significant reduction in death from cardiovascular disease.

The bad news is that a tree disease called Fusarium is on track to kill 26.8 million trees across Southern California in the next few years, almost 40 percent of the trees from Los Angeles to the Nevada border and south to Mexico. That's more than just an aesthetic tragedy. It means that thousands of human beings are going to die, too.

▍生词好句

figure out: it means you have to think about it, and make an effort to solve it. Generally, we intend to figure out something. It does not happen by chance, as in find out.

find out: it means to discover information. Generally, we find out something by chance, in other words, we were not intentionally looking for the information. We happened to discover it.

go out on a limb: put yourself in a dangerous position / at risk because you are doing sth. risky or sth. that doesn't have the support of others. 处于危险的境地；冒险做某事

by dint of: sth. is done as a result of sth. 凭借......；靠......

meta-: meta-: a prefix added to a word, usually a noun that talks about or comments on its own subject or features; it's self-referential, refers to itself ("meta" is an adjective).

take up the issue:  if you take up an issue, a question or a problem, you act on it, or you discuss how you are going to act on it or deal with it.

indeed: adv. in fact / reality / truth 确实；实际上

on track (back on track): if someone / sth. is on track, they are acting / progressing / behaving in a way that is likely to result in success / a certain result