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In the early 1900s, the U.S. Department of Agriculture (USDA) requested an order of Callery pear tree seeds from China.
20世纪初，美国农业部要求从中国订购豆梨树种子。
The agency hoped the seeds might be a solution for a bacterial disease harming American pear production.
该机构希望这些种子可以解决一种危害美国梨产量的细菌性疾病。
Today, however, experts from the USDA are studying the best ways to kill Callery pear trees.
然而，如今，美国农业部的专家们正在研究杀死豆梨树的最佳方法。
The flowering fruit trees have become aggressive, invasive plants.
这种开花的果树已经变成了入侵植物。
University of Cincinnati researchers Theresa M. Culley and Nicole A. Hardiman wrote about the plant's history in 2007 for the publication BioScience.
2007年，辛辛那提大学的研究人员特蕾莎·卡利和妮可·哈迪曼在《生物科学》杂志上撰文介绍了这种植物的历史。
They said that, in the early 1900s, a bacteria called fire blight was badly hurting the production of pears in the U.S.
他们说，在20世纪初，一种名为梨火疫病的细菌严重损害了美国梨的产量。
Scientists discovered that combining a pear tree that produced the edible fruit with the Callery pear tree created a specimen that could survive the bacteria.
科学家们发现，将结出可食用果实的梨树与豆梨树相结合，就创造出了一种可以在该细菌中存活的标本。
Over the years, 25 different kinds of ornamental trees were created from this combination.
多年来，这种组合创造了25种不同的观赏树。
The well-known Bradford pear tree was one of them.
著名的布拉德福德梨树就是其中之一。
All of them were able to survive difficult conditions and were planted across the United States.
它们都能在恶劣的环境中生存下来，并被种植在美国各地。
In 1971, the U.S. Department of Agriculture even created a small publication about their care.
1971年，美国农业部甚至制作了一本有关如何护理它们的小型出版物。
The agency described them as trees that flower several times during the year and do well in many climates and soils.
该机构将它们描述为一年多次开花的树，在许多气候条件下和土壤中都长得很好。
That ability to survive easily is part of what makes the trees invasive.
这种容易存活的能力是这些树具有入侵性的部分原因。
Seeds from the inedible fruit that the trees produce can spread easily.
这些树结出的不可食用的果实种子很容易传播。
In addition, the roots can produce above-ground growth.
此外，它们的根还能在地上生长。
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.
如果不经常加以砍伐以阻止它开花，它可以与树的其余部分一起产生肥沃的种子。
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.
辛辛那提大学的研究人员之一卡利说，野生种群有可能来自某个人在其土地上种植的一棵树。
Callery pear trees are the third most common kind of tree planted along New York City streets, said city parks department spokesman Dan Kastanis.
纽约市公园部门发言人丹·卡斯塔尼斯表示，豆梨树是纽约市街道上第三最常见的树种。
But the city is no longer planting them, Kastanis said.
但卡斯塔尼斯说，该市不再种植它们。
Cities in Virginia, South Carolina, Ohio, and Indiana have also banned or are banning the sale of all kinds of Callery pear trees.
弗吉尼亚州、南卡罗来纳州、俄亥俄州和印第安纳州的城市也已经或正在禁止销售各种豆梨树。
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 remains.
包括密苏里州和阿拉巴马州在内的一些州正在要求房主和地主停止种植这些植物，或者砍掉现有的树，并在剩下的树上使用化学物质。
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.
包括北卡罗来纳州在内的其他州正在向地主免费提供本地树木，只要他们提供照片证明他们已经砍了自家土地里的豆梨树。
Without regular work and attention, fields near seed-producing trees can be covered with small seedlings within a couple of years, said scientist James "J.T." Vogt.
科学家詹姆斯·沃格特说，如果不进行定期的清理和加以注意，种子树附近的田地可能在几年内就会被小树苗覆盖。
He is a scientist at the U.S. Forest Service's Southern Research Station in Athens, Georgia.
他是佐治亚州雅典城美国林务局南方研究站的一名科学家。
"They're a real menace," said Jerrod Carlisle.
杰罗德·卡莱尔说：“它们是真正的威胁”。
He lives in southern Indiana.
他住在印第安纳州南部。
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.
他发现，他自家的四棵树和邻居家的一棵树在20公顷的土地上又创造了数千棵树。
He and his 17-year-old son have cut down an estimated 1,400 Callery pears.
他和他17岁的儿子已经砍了大约1400棵豆梨树。
But he estimates that there are about 1,000 more to go.
但他估计，还要砍大约1000棵豆梨树。
Carlisle thinks he is finally getting ahead of his invasion.
卡莱尔认为他终于赶在了入侵之前。
Native trees that have been planted for reforestation are creating enough shade to finally slow the growth of Callery seedlings.
为重新造林而种植的本地树木正在创造足够的树荫，最终减缓豆梨树幼苗的生长。
I'm Gregory Stachel.
格雷戈里·施塔赫尔为您播报。
译文为可可英语翻译，未经授权请勿转载！
