However, “as horticulturalists tinkered with Callery pears to produce new versions, they made the individuals different enough to escape the fertilization barrier,” McEwan wrote. As wind and birds spread the trees’ seeds, wild populations of the trees became established and started crowding out native species.
Today, Callery pear trees are such scourges that several states have banned them. Others are paying residents to cut them down and replace them with native plants.
2. Tiny organisms, big impacts: Zebra and quagga mussels
Invasive species don’t have to be large to cause outsized damage. Zebra and quagga mussels – shellfish the size of a fingernail – invaded the Great Lakes in the 1980s, clogging water intake pipes and out-competing native mollusks for food. Now they’re spreading west via rivers, lakes and bays, threatening waters all the way to the Pacific coast and Alaska.
As Rochester Institute of Technology environmental historian Christine Keiner wrote, it took several decades for the U.S. and Canada to regulate ships’ management of their ballast water tanks, which was the route by which the mussels were introduced to North America.
“Now, however, other human activities are increasingly contributing to harmful freshwater introductions – and with shipping regulated, the main culprits are thousands of private boaters and anglers,” Keller wrote. Limiting the destructive impacts of invasive species “requires scientific, technological and historical knowledge, political will and skill to persuade the public that everyone is part of the solution.”
However, “as horticulturalists tinkered with Callery pears to produce new versions, they made the individuals different enough to escape the fertilization barrier,” McEwan wrote. As wind and birds spread the trees’ seeds, wild populations of the trees became established and started crowding out native species.
Today, Callery pear trees are such scourges that several states have banned them. Others are paying residents to cut them down and replace them with native plants.
2. Tiny organisms, big impacts: Zebra and quagga mussels
Invasive species don’t have to be large to cause outsized damage. Zebra and quagga mussels – shellfish the size of a fingernail – invaded the Great Lakes in the 1980s, clogging water intake pipes and out-competing native mollusks for food. Now they’re spreading west via rivers, lakes and bays, threatening waters all the way to the Pacific coast and Alaska.
France's second largest listed bank Credit Agricole has decided to replace precious metals with trading in the regulated carbon markets starting from 2025, three