If you were thinking about planting a tree this Fall using the revised USDA Plant Hardiness Zone Map, here's some important news for you: warming temperatures may have already made it obsolete!
The Zone Map predicts which trees and perennials can survive the winter in a given region, and it hadn't been revised since 1990. As expected, temperature boundaries shown in the revised version released earlier this year have shifted northward. However, according to an analysis conducted by Dr. Nir Krakauer, the true zones have moved even farther north.
Krakauer, assistant professor of civil engineering in The City College of New, developed a new method to map cold-weather zones in the United States that takes rapidly rising temperatures into account. Analyzing recent weather data, he overhauled the Department of Agriculture's latest plant zone map released in January.
"Over one-third of the country has already shifted half-zones compared to the current release, and over one-fifth has shifted full zones," Professor Krakauer wrote this summer in the journal Advances in Meteorology.
To create the zone maps, the USDA divides the country into zones based on their annual minimum temperatures, which are used to determine which plants could survive these lows. Professor Krakauer found a weakness in how the USDA came up with the zones, however. The USDA averaged annual minimum temperatures over a 30-year span, from 1976 to 2005, but winters have warmed significantly over that period. Zones now average about 2 degrees Fahrenheit warmer than the USDA's 30-year average.
Professor Krakauer's technique will allow gardeners and farmers to reassess what will survive the next year's winter more frequently than the USDA can produce a new map. "The idea is that you could use this method to keep updating the zone map year by year instead of waiting for the official map - just keep adding new data and recalculate," he said.
Krakauer's hardiness zone warming calculator and hardiness zone change calculators are available online. You might want to check them out before you plant those trees! For more information, see the full text of the research article. The full press release from CCNY also explains the analysis in more detail. Happy planting!
Nir Y. Krakauer. Estimating Climate Trends: Application to United States Plant Hardiness Zones. Advances in Meteorology, Vol. 2012 (2012), Article ID 404876, doi:10.1155/2012/404876
14 Sep 2012 3:52 PM