Something odd has been appearing under streetlights in the American west. The ecologist Dr Shannon Murphy was walking her dog through an alley in Denver, Colorado, when she noticed clumps of invasive cheatgrass flourishing under streetlights. She was already growing prairie grasses in artificially lit greenhouses to study how moths interacted with the plants, but was surprised that cheatgrass thrived under the lights, while native grasses did not see any benefit.
That inspired a team of researchers to survey Denver’s alleys, and they found that cheatgrass was three times more likely to grow under streetlights than in unlit areas, or near utility poles without lights. How streetlights boosted the plant left the scientists baffled, although it could explain why cheatgrass is thriving in many other major urban areas.
Cheatgrass is an alien species invading the western US, threatening farms by displacing natural grasses. It also creates a fire menace because it is an annual plant that dies in late spring, leaving tinderbox-dry vegetation that helps fuel wildfires.
Cheatgrass can recover quickly after such fires, helping it to outcompete perennial native grasses that are much slower to grow back. Cheatgrass seeds also disperse easily, so the plant can spread rapidly.
