They can dilute the wild varieties, threatening their existence.
A scientist from the UK wants people to stop throwing apple cores out the car window. After conducting a study of apple trees along the sides of the M9 and A9 highways in Scotland, Dr. Markus Ruhsam, a botanist and molecular ecologist at the Royal Botanic Gardens in Edinburgh, has discovered that more than half have sprouted from supermarket apple varieties that have most likely been pitched out a car window in passing. This is a concern because the cultivated varieties cross-pollinate with wild apples to create hybrids that could lead to the eventual demise of wild varieties.
Ruhsam conducted genetic testing of apple trees throughout Scotland and found that, despite many trees looking wild, approximately 30 percent are hybrids. The Telegraph reported,
"Nowhere was found to have entirely wild trees, but researchers discovered that in areas where ancient woodland is more common, up to nine in 10 crab apple trees are pure. Those last bastions included the southern Highlands, particularly around the Loch Lomond and Trossachs National Park, parts of Dumfries & Galloway and The Lake District."
Amateur apple growers are part of the problem, as their cultivated trees can cross-pollinate with nearby wild ones to create hybrids; but Ruhsam also thinks that tossing apple cores out the car window needs to stop. He is quoted in the Telegraph:
"I wouldn’t want to discourage people from planting apple trees in their gardens. What I would like to discourage is people randomly planting apple trees in the wild. We want to keep wild apples wild. Another thing is not chucking your apple core out of the window. I’m guilty of it as well."
The cultivated apples we enjoy now do originate from wild species, but have undergone an extensive evolution from their original form. They are much sweeter and larger than their crab apple ancestors, but crab apples still deserve a protected place in our world. They have a rich history of literary references and provide shelter to numerous small animals.