"In the 1960s and '70s, the Minneapolis urban forest was 90 percent elms," North said. "They grew well here, they were beautiful. When Dutch elm disease struck, all those trees went away. The city did a very thoughtful job of diversifying. Now there is no one species that accounts for more than 30 percent of the urban forest. There will always be the next pest or pathogen — emerald ash borer, for example — but ash trees are only 24 percent of the urban system. Diversity makes the system more stable."
Read the full article at the Minneapolis StarTribune.