VOA健康报道2022--Invasive Fruit Tree Reported Across the US

Invasive Fruit Tree Reported Across the US

In the early 1900s, the U.S. Department of Agriculture (USDA) requested an order of Callery pear tree seeds from China. The agency hoped the seeds might be a solution for a bacterial¹ disease harming American pear production.

Today, however, experts from the USDA are studying the best ways to kill Callery pear trees. The flowering fruit trees have become aggressive, invasive plants.

University of Cincinnati researchers Theresa M. Culley and Nicole A. Hardiman wrote about the plant’s history in 2007 for the publication BioScience. They said that, in the early 1900s, a bacteria called fire blight² was badly hurting the production of pears in the U.S. Scientists discovered that combining a pear tree that produced the edible³ fruit with the Callery pear tree created a specimen⁴ that could survive the bacteria.

Over the years, 25 different kinds of ornamental⁵ trees were created from this combination. The well-known Bradford pear tree was one of them. All of them were able to survive difficult conditions and were planted across the United States.

In 1971, the U.S. Department of Agriculture even created a small publication about their care. The agency described them as trees that flower several times during the year and do well in many climates and soils.

That ability to survive easily is part of what makes the trees invasive.

Seeds from the inedible⁶ fruit that the trees produce can spread easily. In addition, the roots can produce above-ground growth. If the growth is not cut down often to stop it from flowering, it can create a fertile seed with the rest of the tree.

It is possible for a wild population to come from a single tree that someone plants on their property, said Culley, one of the University of Cincinnati researchers.

Callery pear trees are the third most common kind of tree planted along New York City streets, said city parks department spokesman Dan Kastanis.

But the city is no longer planting them, Kastanis said. Cities in Virginia, South Carolina, Ohio, and Indiana have also banned or are banning the sale of all kinds of Callery pear trees.

Some states, including Missouri and Alabama, are asking homeowners and landowners to stop planting them or to cut existing ones down and use chemicals on what remains⁷. Other states, including North Carolina, are offering free native trees to landowners who show photographic evidence that they have cut down Callery pears on their property.

Without regular work and attention, fields near seed-producing trees can be covered with small seedlings⁹ within a couple of years, said scientist James “J.T.” Vogt. He is a scientist at the U.S. Forest Service’s Southern Research Station in Athens, Georgia.

“They’re a real menace,” said Jerrod Carlisle. He lives in southern Indiana. He discovered that four trees on his property and one on his neighbor’s property had created thousands more of the trees on 20 hectares of land.

He and his 17-year-old son have cut down an estimated 1,400 Callery pears. But he estimates that there are about 1,000 more to go.

Carlisle thinks he is finally getting ahead of his invasion. Native trees that have been planted for reforestation are creating enough shade to finally slow the growth of Callery seedlings.

Words in This Story

edible – adj. suitable or safe to eat

specimen – n. something (such as an animal or plant) collected as an example of a particular kind of thing

ornamental – adj. used to make something more attractive: used for decoration

seedling⁸ – n. a young plant that is grown from seed

menace – n. a dangerous or possibly harmful person or thing

shade – n. an area of slight darkness that is produced when something blocks the light of the sun

1 bacterial   

a.细菌的

参考例句：

• Bacterial reproduction is accelerated in weightless space. 在失重的空间，细菌繁殖加快了。
• Brain lesions can be caused by bacterial infections. 大脑损伤可能由细菌感染引起。

2 blight   

n.枯萎病；造成破坏的因素；vt.破坏，摧残

参考例句：

• The apple crop was wiped out by blight.枯萎病使苹果全无收成。
• There is a blight on all his efforts.他的一切努力都遭到挫折。

3 edible   

n.食品，食物；adj.可食用的

参考例句：

• Edible wild herbs kept us from dying of starvation.我们靠着野菜才没被饿死。
• This kind of mushroom is edible,but that kind is not.这种蘑菇吃得，那种吃不得。

4 specimen   

n.样本，标本

参考例句：

• You'll need tweezers to hold up the specimen.你要用镊子来夹这标本。
• This specimen is richly variegated in colour.这件标本上有很多颜色。

5 ornamental   

adj.装饰的；作装饰用的；n.装饰品；观赏植物

参考例句：

• The stream was dammed up to form ornamental lakes.溪流用水坝拦挡起来,形成了装饰性的湖泊。
• The ornamental ironwork lends a touch of elegance to the house.铁艺饰件为房子略添雅致。

6 inedible   

adj.不能吃的，不宜食用的

参考例句：

• The food was totally inedible.食物完全无法下咽。
• These chemicals make the fruit inedible.这些化学品使这种水果不宜食用。

7 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

8 seedling   

n.秧苗，树苗

参考例句：

• She cut down the seedling with one chop.她一刀就把小苗砍倒了。
• The seedling are coming up full and green.苗长得茁壮碧绿。

9 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》