In January 2012, the US Department of Agriculture released the “Plant Hardiness Zone Map”. Planting guidelines were provided, showing which trees are most likely to withstand the winter months.
The map has already been made obsolete as researchers have devised a new method of mapping cold weather zones. The country was originally divided into zones depending on annual average temperatures taken between 1976 and 2005.
The revised method considers rapidly rising temperatures, resulting in a 2 degree Farenheit warmer recording than the previous 30 year average. Over one third of the country has shifted half-zones.