If you drive through town at this time of year, one of the first trees to bloom is the Bradford or Callery pear tree. They’re covered in big white flowers and since nothing’s blooming yet, you can tell they’re everywhere.
This reminds us of a popular line in the movie Jurassic Park. A scientist scoffs at the idea that the park’s dinosaurs were biologically engineered to prevent them from reproducing. The scientist has no faith that they really won’t reproduce, saying, “Life will find a way.”
In fact, the next movie found hatched dinosaur eggs in the wild, showing that life did indeed find a way.
While not as dangerous as reproducing dinosaurs, a similar story is playing out in our own backyards and parks, and it involves the Bradford/Callery pear tree. Scientists once boasted that they were safe here because they were genetically engineered never to reproduce.
Why scientists thought the Bradford pear was ‘safe’
However, the Bradford pear tree is different. Scientists brought this tree species over to use as ornamental landscape trees in gardens. The trees are not the fruit trees you think of when you think of pear trees. These trees only produce berries that we cannot eat.
They live freely in China and cause no problems at all. They grew quickly and were resistant to many different pests. Best of all, the trees were unable to pollinate with other Callery pear trees and therefore failed to reproduce. A plant cannot be invasive if it cannot reproduce.
Life will find a way
As always, the plan didn’t quite work out as hoped. In fact, Callery pear trees cannot self-pollinate or be pollinated by the same species of tree.
However, then mistakes were made as people worked with genetics to create different lineages of these pear trees to create a tree with even better characteristics.
The newly created pear tree lines were similar enough to the original Callery pear trees but different enough that they could now cross-pollinate to produce fertile seeds that would produce new, wild Callery pear trees.
These new, wild trees were able to produce fruitful seeds every year and since then this tree has conquered vast fields and forests. It has become a real invasive species.
Life has found a way – and it’s suffocating other species that our natural ecosystem counts on to stay in balance.
Why are these trees a problem for us but perfectly fine in China? China has other trees and organisms that keep the Callery pear trees in check. We don’t have the same competitors to keep our invading trees under control.
Problems with the pear trees
In addition to becoming invasive, this tree has other problems that make it unloved by homeowners who have it. The trees grow incredibly fast, which often means the wood is very soft. Soft wood breaks in strong winds and heavy snowfall. The majority of the branches that fall after a spring or summer storm are from Callery pear trees. This often costs owners far more than the original trees in the tree felling service.
Another problem is the flowers of the tree. These flowers are one of the reasons people love these trees, but as the trees grow taller and have more flowers, their owners realize that the flowers produce an odor that reminds people of rotting meat. Nice!
Simple solutions we can adopt
Controlling invasive callery pear trees is not as difficult as controlling invasive honeysuckle since the pear trees have not yet taken up as much land as the honeysuckle.
The first step in controlling this growing problem is to remove all Callery/Bradford pear trees on your property and stop buying the trees. Once you’ve cut down the problem tree, replace it with a tree native to the area, such as redbud, oak, maple, or dogwood.
What happens if we don’t address the problem of invasive species? Again life will find a way. We’ll still have ecosystems – they just won’t be what we’re used to. Most importantly, organisms dependent on native species will be disrupted and possibly replaced by other non-native species.
Mike Szydlowski is a science teacher and zoo director at Jefferson STEAM School.
TIME FOR A POP QUIZ
What is an invasive species?
What is the same and what is different between invasive and non-native species?
Should farmers stop growing the pears we eat? Why or why not?
Why are most of our invasive species not a problem in their original habitat?
If you find a store that still sells ornamental pear trees (not fruit trees), what could you do to improve the situation?