VOA标准英语2011--Vines Overwhelming Trees in Rain Forests

Vines Overwhelming Trees in Rain Forests

Tropical rain forests in the American Hemisphere and other regions of the world are changing rapidly. Studies conducted over recent decades indicate that increasingly, most of the trees in South and Central American rain forests must compete for light and nutrients¹ with "lianas" or woody vines. Studies also show that lianas are growing so abundant as a result of climate change and higher levels of carbon dioxide in the atmosphere that they are overwhelming their host trees, and in some cases, killing² them.
Deep in the tropical forest of Panama, on the island known as Barro Colorado, scientists from the Smithsonian Tropical Research Institute have been studying the flora³ and fauna⁴ for nearly 100 years.
Stefan Schnitzer is one of those scientists. He studies "lianas" or woody vines, structural⁵ parasites⁶ that require trees for support. He found out that vines growing on tree crowns have more than doubled over the last four decades.
"What we found is that probably about 80 percent of the trees that are around us now have some competition with vines," Schnitzer noted⁷. "Vines are affecting nearly all of the trees. So most of their growth rate is being reduced because of vines."
Not only growth. Lianas compete for nutrients in the soil, deprive trees of light, and can choke and kill them.
"You can call them natural born killers," Schnitzer added. "What's very interesting about these lianas is they climb up a tree, that tree falls, the liana falls with it, but the tree dies and the liana stays alive."
Schnitzer estimates that some lianas are hundreds of years old, cover dozens of trees at one time and stretch for nearly a kilometer over tree tops.
Although some lianas produce fruits and habitat for animals, they are devastating⁸ for most trees. One liana we found had more than 10 different rooting points within a few square meters.
"This is an enormous liana and it's rooted right there next to the tree; it's competing for all sorts of resources," Schnitzer explained. "And then, to add insult to injury, it's sending this giant stem up into the canopy⁹ where is competing for light as well."
Schnitzer says he believes lianas are growing faster because of drought and warmer temperatures. He says these woody vines prevent trees from growing and capturing carbon dioxide.
In another clearing we saw, there were no trees, the vines had completely taken over.
"What you get is tree gaps that never recover or take them 20-30 years to recover back to full canopy, because there are so many lianas preventing trees from growing," Schnitzer said.
Schnitzer and his team are also working on the nearby peninsula of Gigante in another protected area. Here, hundreds of tree seedlings¹⁰ from 14 native species are ready to be planted.
Schnitzer's team will plant these seedlings in 16 plots, half with lianas and half without them.
"We will measure mortality or survival every 2-3 months, and then we measure growth every 6 to 12 months. And after two or three years we'll know which tree species are going to regenerate¹¹ better when lianas are present versus¹² when lianas are absent," Schnitzer explained.
At the end of 20 years, Schnitzer says they will know how the tropical forest is changing and how to restore and conserve¹³ it.
"The forests are changing and moving in a direction that may result in more liana- dominated forest and forests dominated by trees that can tolerate lianas," Schnitzer said.
Why should we care? Because, Schnitzer says, tropical forests contain about one third of all global terrestrial carbon. Without trees to capture that carbon dioxide, global climate change would be an even greater threat.

1 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》

2 killing   

n.巨额利润；突然赚大钱，发大财

参考例句：

• Investors are set to make a killing from the sell-off.投资者准备清仓以便大赚一笔。
• Last week my brother made a killing on Wall Street.上个周我兄弟在华尔街赚了一大笔。

3 flora   

n.(某一地区的)植物群

参考例句：

• The subtropical island has a remarkably rich native flora.这个亚热带岛屿有相当丰富的乡土植物种类。
• All flora need water and light.一切草木都需要水和阳光。

4 fauna   

n.(一个地区或时代的)所有动物，动物区系

参考例句：

• This National Park is an area with unique fauna and flora.该国家公园区域内具有独特的动物种群和植物种群。
• Fauna is a biological notion means all the animal life in a particular region or period. 动物群是一个生物学的概念，指的是一个特定时期或者地区的所有动物。

5 structural   

adj.构造的，组织的，建筑（用）的

参考例句：

• The storm caused no structural damage.风暴没有造成建筑结构方面的破坏。
• The North American continent is made up of three great structural entities.北美大陆是由三个构造单元组成的。

6 parasites   

寄生物( parasite的名词复数 )； 靠他人为生的人； 诸虫

参考例句：

• These symptoms may be referable to virus infection rather than parasites. 这些症状也许是由病毒感染引起的，而与寄生虫无关。
• Kangaroos harbor a vast range of parasites. 袋鼠身上有各种各样的寄生虫。

7 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

8 devastating   

adj.毁灭性的，令人震惊的，强有力的

参考例句：

• It is the most devastating storm in 20 years.这是20年来破坏性最大的风暴。
• Affairs do have a devastating effect on marriages.婚外情确实会对婚姻造成毁灭性的影响。

9 canopy   

n.天篷，遮篷

参考例句：

• The trees formed a leafy canopy above their heads.树木在他们头顶上空形成了一个枝叶茂盛的遮篷。
• They lay down under a canopy of stars.他们躺在繁星点点的天幕下。

10 seedlings   

n.刚出芽的幼苗( seedling的名词复数 )

参考例句：

• Ninety-five per cent of the new seedlings have survived. 新栽的树苗95%都已成活。 来自《现代汉英综合大词典》
• In such wet weather we must prevent the seedlings from rotting. 这样的阴雨天要防止烂秧。 来自《现代汉英综合大词典》

11 regenerate   

vt.使恢复，使新生；vi.恢复，再生；adj.恢复的

参考例句：

• Their aim is to regenerate British industry.他们的目的是复兴英国的工业。
• Although it is not easy,you have the power to regenerate your life.尽管这不容易，但你有使生活重获新生的能力。

12 versus   

prep.以…为对手，对；与…相比之下

参考例句：

• The big match tonight is England versus Spain.今晚的大赛是英格兰对西班牙。
• The most exciting game was Harvard versus Yale.最富紧张刺激的球赛是哈佛队对耶鲁队。

13 conserve   

vt.保存，保护，节约，节省，守恒，不灭

参考例句：

• He writes on both sides of the sheet to conserve paper.他在纸张的两面都写字以节省用纸。
• Conserve your energy,you'll need it!保存你的精力，你会用得着的！