Those who are old enough can remember how neighborhoods changed overnight with the onslaught of Dutch elm disease. Old, majestic elms, whose branches intertwined above streets like the arches of some organic Gothic cathedral, came down by the hundreds.

People on the ground below were left to bake in the glaring summer sun and gaped in the fall when they realized the annual golden canopy was gone for good and wondered, what the hell just happened?

This summer just about all of the 560 ash trees left in Riverside will be gone. Just eight years ago there were 1,100 ashes in the village. But the emerald ash borer either wiped them out or threatened to, and they needed to go.

That means people who lived through what appeared to be endless removals of elm trees may feel a pang of regret at the loss of so many trees in one season.

But, the lesson of Dutch elm and of the emerald ash borer is that a diverse tree stock and principally native trees are what make a healthy, sustainable urban forest. While the loss of ashes is regrettable, it sets the stage for Riverside to continue to strengthen its natural infrastructure — the thing that’s made Riverside the unique, beautiful village it has been since 1870.