Non-native plant species are much more widespread than natives.
A new study, the first comprehensive assessment of native vs. non-native plant distribution in the continental United States, finds non-native plant species are much more widespread than natives, a finding that lead author Bethany Bradley at the University of Massachusetts Amherst called “very surprising.”
“Ecologists typically think of invasive species as being introduced in one spot and gradually spreading out from there. But, we found that even species with only a handful of occurrences were distributed all across the U.S.,” she says. “The future may already be here.”
The international team explored the geographic distributions of over 13,000 plant species, comparing those that are native and non-native to the continental United States, to identify differences in their overall geography. Their comparative analysis highlights the fact that native plants are strongly limited in their distributions compared to non-native plants, probably because they have a harder time dispersing into suitable climates. That is, people aren’t moving them around as much, Bradley says.
The researchers analyzed the distributions of 13,575 plant species (9,402 native, 2,397 endemic, 1,021 alien and 755 invasive) across the U.S. For each species, they recorded the total number of grid cells (roughly county-sized) occupied, calculated potential range based on climatic conditions, and measured their latitudinal and longitudinal extents. They then used the number of occupied and potential grids to calculate occupancy of potential range (range infilling) for each.
Bradley says although non-native and invasive species are much more widespread than natives, they have “filled in” much less of their potential range. Native species on average occupied about 50 percent more of their potential range than non-native species. For managers dealing with invasive species, Bradley says, “watch out.”
She adds, “We’re likely to see more problems from invasive species ahead as they continue to expand locally into suitable environments.” As the paper title states, invasive plants have plenty more space to invade. (2015) January University of Massachusetts Amherst Press Release.