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Invasive species get a bad rap—but we humans are usually to blame for their spread. Take Japanese stiltgrass, an invasive that arrived from Asia nearly 100 years ago as a packing material for porcelain¹. When it creeps into forests, it forms dense² carpets that can choke out native tree seedlings³. And in the last 15 years, the grass has infested⁴ rural roads throughout Pennsylvania's Rothrock State Forest—much faster than foresters expected.

Researchers thought the cause could be another human activity—road maintenance. They spray-painted 320,000 dead safflower seeds, and placed them along state forest roads. After routine road grading, they combed through the gravel⁵ to recover them. And they found that some seeds had been carried hundreds of feet down the road. Much farther than the few feet seeds can travel on their own—perhaps explaining the grass' rapid spread.

They presented those results at a meeting of the Ecological⁶ Society of America.

Still, roads need to be safe for drivers. So the researchers propose smoothing shorter segments at a time, or doing it less frequently. Because where humans go, invasives often follow—whether by sea or on land.

Thanks for the minute. For Scientific American's 60-Second Science, I'm Christopher Intagliata.

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1 porcelain
n.瓷；adj.瓷的，瓷制的
参考例句：
These porcelain plates have rather original designs on them.这些瓷盘的花纹很别致。 The porcelain vase is enveloped in cotton.瓷花瓶用棉花裹着。

2 dense
a.密集的，稠密的，浓密的；密度大的
参考例句：
The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。 The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。

3 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》

4 infested
adj.为患的，大批滋生的（常与with搭配）v.害虫、野兽大批出没于( infest的过去式和过去分词 )；遍布于
参考例句：
The kitchen was infested with ants. 厨房里到处是蚂蚁。 The apartments were infested with rats and roaches. 公寓里面到处都是老鼠和蟑螂。

5 gravel
n.砂跞；砂砾层；结石
参考例句：
We bought six bags of gravel for the garden path.我们购买了六袋碎石用来铺花园的小路。 More gravel is needed to fill the hollow in the drive.需要更多的砾石来填平车道上的坑洼。

6 ecological
adj.生态的，生态学的
参考例句：
The region has been declared an ecological disaster zone.这个地区已经宣布为生态灾难区。 Each animal has its ecological niche.每种动物都有自己的生态位.