For 230 years, since the times of the French Revolution, a white ash tree grew in a forest beside a stream that much later became part of Baltimore. My house was built it its shadow in 1904. And by the time I moved in in 1998, its trunk was five feet across.
It was on this tree that I built a rope swing that my daughters – now off to college – flew on in their white first communion dresses when they were young. Then all the neighborhood kids adopted the swing, to play on after school.
Last week, I called in a tree crew with a crane to cut it down.
The white ash had been infected with an invasive species of flying beetle from Asia: the emerald ash borer, which has been killing millions of ash trees across Maryland and the Eastern U.S. over the last decade and a half.
The loss of ash trees across my neighborhood in North Baltimore and the U.S. made me reflect on the often catastrophic impact of invasive species and globalization on our environment.
The journal Science last month reported that the spread of an almost invisible fungus called chytrid perhaps originally from Korea, is killing off frogs and salamanders around the world at a rate faster than anyone thought. At least 500 amphibian species are in decline because of the chytrid fungus, and 90 species have gone extinct because of it.
One might expect that Asia – as the largest landmass on the globe, with the most species and therefore the most intra-species competition – would be the source of most of the invasive species elsewhere. But even life forms native to North America are wreaking havoc when they are accidentally transported in ships around the world.
The Chesapeake Bay’s feisty blue crab, for example, has spread in ship ballast water into Mediterranean Sea, where it is now multiplying and threatening to outcompete crabs native to Europe.
American bullfrogs, exported to Asia and South America as food, have escaped from their frog farms and are exploding in numbers, gobbling up local species of amphibians. Oddly enough, these American frogs are spreading the Asian chytrid fungus, to which they appear to be immune.
Not all exotic species are harmful. For example, the common aquarium plant hydrilla – originally from Asia – was seen as threat when it started spreading in the Potomac River in the 1980s. But biologists later concluded that the fast-growing plant was beneficial, because it stabilized the barren river bottom, providing habitat for fish and native plants, and food for ducks and geese.
Fear of globalization is now driving American politics, most prominently by President Trump’s crusade to wall out immigrants from Mexico. Blue collar workers are angry that American manufacturing jobs are migrating overseas.
It would be impossible to stop globalization – and perhaps dangerous to try. But that doesn’t mean we should just throw up our hands and say we can’t do anything about it. We can improve conditions in our own back yard.
In my case, to replace my infected white ash tree, I planted a new native species: an American sycamore. It was in some ways painful to see the inch-wide sapling looking scrawny where the majestic ash had once soared.
But I have faith the stick will eventually grow to a towering beauty, with its white and brown skin and seed balls dangling like ornaments on a Christmas tree. It will be a gift to future generations.
