The deadly meteorite that wiped out the world's dinosaurs 66 millions years ago also devastated the forests of North America, setting the stage for a competition that saw winners and losers in the leafy rivalry that ensued, scientists say.
The massive impact, with its mega tsunamis and wildfires decimated evergreen plants to a much greater extent than deciduous varieties, they say, leading to new forests that would have been foreign to any plant-eating dinosaur.
"When you look at forests around the world today, you don't see many forests dominated by evergreen flowering plants," says study lead author and ecologist Benjamin Blonder. "Instead, they are dominated by deciduous species, plants that lose their leaves at some point during the year."
In the vast woodlands stretching from Mexico to Canada, more than half of all plant species became extinct in the harsh conditions following the impact off Mexico's Yucatan Peninsula, setting up a competition among surviving plant species to see which ones would dominate in the new climate conditions.
The slow-growing trees and shrubs that had fed the dinosaurs for millions of years had trouble adapting to the climate swings that followed the meteor impact, the researchers say.
Deciduous species recovered much more quickly than evergreens, they report in a study published in PLOS Biology.
Ecosystems in the colder and darker years following the event, known as the impact winter, favored faster-growing plants, they say.
The researchers studied thousands of preserved leaves in a fossil formation in North Dakota to find out which plants were better equipped to withstand the harsher climate.
They looked at a measure known as leaf mass versus area, an indication of the amount of carbon plants need to invest to grow leaves.
"[This] tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one," Blonder says.
In the dark impact winter, leaves would have been a drain on a plant's resources when photosynthesis was curtailed, creating a burden for the evergreen species that never dropped their leaves, the researchers suggest.
That favored deciduous species, which could drop their leaves for a portion of the year and reduce the resource drain, says Blonder.
"Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species," he says.
It also suggests the extinction of plant species was not random and why modern forests are for the most part deciduous rather than evergreen, he added.
