How the Plant Hardiness Zones are Causing Trees to Move North
The USDA Plant Hardiness Zone Map is invaluable to gardeners and growers to determine which trees, shrubs, and plants will thrive in specific locations across the United States based on weather patterns and temperatures. But climate change is forcing many trees to adapt to warmer temperatures and extended periods of drought – forcing them to go north where conditions are still ideal.
Visit the USDA Plant Hardiness Zone Map to find the interactive map graphic.
With temperatures rising in southern locations, a tree’s growing range (the conditions in which optimal growth and sustainability are possible) is now moving further north, leaving plant hardiness zones in more southern areas of the country struggling to find trees that can sustain the impacts of climate change.
The USDA Plant Hardiness Zones are divided into thirteen zones based on a location’s annual minimum temperatures over a 30-year period, and each zone has a ten-degree range in average annual minimum temperature.
While trees, shrubs, and plants have always had to adjust to drastic changes in climate, over the last century, the earth’s temperature has warmed ten times faster than during the end of the historical ice ages. This accelerated warming is making it difficult for trees to adapt gradually to warmer temperatures and drier conditions, and thus, they’re abandoning these locations for more tolerable conditions.
Climate change often stresses trees, shrubs, and plants, leading them to seek more ideal growing conditions over time. Stressors include:
Lower Productivity
Drier conditions or periods of extreme heat prevent trees, shrubs, and plants from growing optimally, stunting their growth over time. As trees are vital to our ecosystem, the decrease in growth will undoubtedly impact wildlife habitats and food sources, forcing them to move elsewhere.
Invasive Plants
When weather patterns change, native species no longer hold an advantage, which allows more invasive species an opportunity to thrive and overtake an area. Many invasive species can actually strangle or choke the root systems of native species until they have completely obliterated them.
Insects and Diseases
As climate change disrupts trees, shrubs, and plants’ resiliency, they are more susceptible to pests and diseases they were able to combat in the past. Warmer temperatures also mean insects will survive the winter increasing their damaging populations come the spring.
Since trees cannot move to new locations on their own, the migration northward happens in the form of seed spreading, which is often carried by river currents, wind, or even by birds and rodents. Once the seed lands in a new environment, if the conditions are ideal, the seed will sprout and spread. If not, it will simply die out.
With the current warming trend occurring in the southern part of the United States, if seeds are transported to more hospitable growing locations, the tree species could stay viable in other regions while becoming extinct in areas where trees cannot adapt to the rapidly changing weather patterns.
While homeowners often experiment with new trees on their property, it is recommended to consult a certified arborist before purchasing and planting.
Doug Tallamy, professor of agriculture and natural resources at the University of Delaware, says trees “are decorations, but they have ecological functions, too. There is more to consider than will it live here: Will it perform here? Will it function here? Will it support the insects and then the birds that depend on that tree here?”
To see a map of how the plant hardiness zones are predicted to change, click here.
For more information on what types of trees you should plant on your property, call your local SavATree branch today.
