Many climate change plans include planting billions of trees to clean the air, protect water sources and cool down cities. But a new study published in Bioscience found that U.S. tree nurseries don’t grow enough trees to meet these goals. Nor do they have the species diversity needed to improve urban trees’ resilience towards invasive pests, air pollutants and other stressors.
“Trees are this amazing natural solution to a lot of our challenges, including climate change. We urgently need to plant many millions of them,” said Tony D’Amato, study co-author and forest ecologist at the University of Vermont, in a statement.
However, according to the study, there might not be enough seedlings to accomplish this.
Why Do We Need Trees?
Trees do more for our health than just clean up the air we breathe. Being around trees lowers stress, improves cognition and boosts longevity. They also cool cities by up to 2.9 degrees Fahrenheit when comparing urban forests to unforested urban areas.
Because of this, D’Amato, and his team looked at 605 plant nurseries in 20 northern states to see if there were enough nurseries for an increase in planting. Out of those 605, only 56 nurseries grow and sell tree seedlings in amounts needed for reforestation and conservation goals, and 14 of the nurseries studied were government operated.
How the Seed Shortage Impacts Reforestation
The team also found that the nurseries lacked a diverse selection of species and seedlings adapted to local conditions and weather. The tree seeds on hand often had commercial timber value over other species needed to conserve and restore forests in a warmer future.
“We know we’re losing ecologically important species across North America and around the world. So, the goal is: can we restore these trees or replace them with similar species? It’s a powerful idea,” said Peter Clark, the new study's lead author and forest ecologist at the University of Vermont in a statement.
Planting Trees for Climate Change Mitigation
Ecologists found that while the number of seeds is one challenge, there is also a bigger challenge: curating seed collections with species needed to restore ecologically complex forests and support diverse flora and fauna.
Red spruce, for example, is an ecologically important species found in eastern North America that has been under climate stress, pests and deforestation for decades. Despite this, only two tree nurseries out of the study’s survey of 20 states had red spruce. In 2022, only 800 red spruce seeds were commercially available for purchase. That many seeds only reforests less than one hectare. To meet restoration goals, conservationists need millions of seeds.
“It really points to just how bare the cupboard is when it comes to the diversity of options,” said D’Amato. “But also, the quantity that's needed to make any meaningful impact.”
Diverse Tree Species Needed
When planting trees along the sidewalks of cities, it’s better to have multiple species of native trees lining the streets. If there is just one type of tree, urban forests are vulnerable to species-specific pests and diseases, such as the emerald ash borer.
This pest is an invasive jewel beetle that has destroyed 40 million trees in Michigan alone and tens of millions in North America. The Dutch elm disease, a fungus called Ophiostoma ulmi, has also decimated 90 percent of American elms that lined the streets of large metropolitan areas since the 1930s.
Investing in Tree Nurseries to Fight Climate Change
The study's researchers argue that increasing seedling production and diversity in nurseries across North America is key to addressing climate change. But, the idea, the authors note, is not without risks involved. Investments have to be made in growing trees that are more adapted to the changing climate, and it might be a high financial risk. There are also less tree nurseries overall.
Seeds also need to originate from areas similar to the geographic or bioclimatic zones they are planted in because seeds brought from an outside region are less likely to succeed. Aside from this, younger seeds are more susceptible to stress and may not survive misalignment with seasons on when they can be planted.
“People want trillions of trees,” said Clark, “but often, on the ground, it’s one old farmer walking around to collect acorns. There’s a massive disconnect.”