They're intensely competitive and eminently successful at crowding out native cottonwoods and willows.
Fire is one of their tools.
In the past two weeks, a series of wildfires have scorched more than 2,600 acres of bosque - the riverside forest that creates a green ribbon oasis through the middle Rio Grande valley. Unlike forest fires in the mountains, fire in the bosque is generally considered bad for the ecosystem. Wildfires in mountain forests prepare the ground for aspen seedlings and prompt some conifer seeds to open. Flooding has historically filled that role in the bosque. Fires, on the other hand, kill cottonwoods while giving salt cedars and other non-native species an added boost.