Invasive species get a bad ___1___—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 porcelain. When it creeps into forests, it forms dense carpets that can ___2___ native tree seedlings. And in the last 15 years, the grass has ___3___ rural roads throughout Pennsylvania's Rothrock State Forest—much faster than foresters expected.

Researchers thought the cause could be another human activity—___4___. They spray-painted 320,000 dead safflower seeds, and placed them along state forest roads. After routine road ___5___, they combed through the gravel 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 Ecological Society of America. [Emily Rauschert and David Mortensen, Human-mediated spread of invasive plants across a landscape]

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.
【视听版科学小组荣誉出品】
rap choke out infested road maintenance grading
入侵物种引来骂声一片——而令它们迅速蔓延的却是我们人类。柔枝莠竹就是入侵物种之一，它是一种瓷器垫料，一百多年前从亚洲传入。柔枝莠竹渐渐在森林里蔓延开来，形成厚厚的一层“地毯”，阻碍当地树木幼苗的生长。过去15年里，柔枝莠竹遍布宾夕法尼亚州立原始森林公园的小路上，蔓延速度比林业学家预期得要快得多。 研究人员认为造成这种后果可能是因为另一项人类活动——道路维修。他们喷涂了32万株干红花种子，把它们铺在公园道路旁。道路频繁维护之后，它们从石砾缝中钻出来重新覆盖路面。研究人员还发现有些种子是从几百英尺的地底下被带出来的，要比它们自己上窜的距离大多了——这也许能解释柔枝莠竹迅速蔓延的原因。 研究人员在美国生态学会的一次会议上公布了这项研究结果。 然而道路安全仍然相当重要，于是研究人员提议每次少翻修一点路段，或者不要翻修得太频繁。漂洋过海，跋山涉水，不管怎样，人类走到哪里，入侵物种就跟到哪里。