Warming trend visible in the trees

Rising temperatures are allowing Southern trees to thrive farther north and stressing trees used to colder weather, according to new national guidelines issued by planting experts.

The National Arbor Day Foundation last month updated the Agriculture Department’s “hardiness zones” map, which was last issued in 1990. The group acted after noticing that some tree species were thriving where they had not before, while others were doing poorly in what had been a suitable region on previous maps.

The shift in zones may allow people in northern areas to experiment with flowering Southern trees such as apple and cherry where they used to plant only fir, spruce and pine, says group spokesman Woodrow Nelson.

The map divides the nation into 11 planting zones tied to average low temperatures. It shows significant boundary changes as the continent has warmed. For example, in southern Texas, the edge of one zone moved more than 200 miles north to the Panhandle. A few locations jumped two zones.

USA Today