By the end of the century, Alabama cherry trees might find themselves unwelcome in Montgomery, replaced by blue jacarandas, now native to Latin America. In Washington, D.C., cabbage palmettos — the state tree of Florida and South Carolina — could thrive, while Fraser firs — popular as Christmas trees — could die out.
As greenhouse gas emissions nudge temperatures higher, trees’ growing ranges are shifting northward, projections from the U.S. Forest Service show. Trees near the southern edge of their geographic ranges — what scientists refer to as “plant hardiness zones” — will be left behind, while northern latitudes will welcome new species from the south.
Plant hardiness zones represent the 30-year average of the coldest temperature at each location across the country. Zones increase with each 10-degree Fahrenheit (5.6-degree Celsius) interval. Factors besides extreme cold — such as soil, rainfall and humidity — influence which trees grow.
“The hardiness zones have always been a useful tool — not necessarily a Bible — but a tool to help people think about what they’re planting and why and where,” said Dan Lambe, the Arbor Day Foundation’s chief executive.