Last year’s Castle Fire in California’s Sierra Nevada is estimated to have killed more than 10 percent of the world’s giant sequoias, the largest trees on earth. Sequoias can live through many fires over life spans that last thousands of years; their bark is fire-resistant and they rely on fire to reproduce. But as climate change intensifies, wildfires are growing larger and more intense. According to state officials, six of the seven largest wildfires in California history took place roughly within the past year.
To help restore fire-ravaged forests and temper the effects of climate change, a handful of young companies want to scatter seeds from drones. At least three—Dendra Systems, CO2 Revolution, and Flash Forest—have pledged to plant a billion trees, or more.
But it’s not clear how effective drone-led reforestation can be. One study found that fewer than 20 percent of seeds dropped by drone take root and grow into trees. None of the companies contacted by WIRED would disclose how many trees they’ve successfully grown to date.
Now, there’s a new obstacle: a seed shortage that’s expected to last for years is prompting forestry officials to make the most of every seed they have.
After the Castle Fire, the California Department of Forestry and Fire Protection considered working with DroneSeed, a Seattle company that uses drones the size of washing machines to plant trees within six months of a fire, to help restore Mountain Home State Forest. DroneSeed is the only company in the US with FAA approval to fly multiple drones more than 55 pounds beyond line of sight, but the plan was put on hold.
Chief Stewart McMorrow, supervisor of the Cal Fire Reforestation Center, which has run the state’s tree seed bank since the 1950s, says planting trees with drones may have merit. But he says it’s hard to test the idea when seeds are scarce, because so few of the drone-scattered seeds will turn into trees.
“We absolutely want to make the DroneSeed option work, but the way that it is functioning right now, it is not a viable option, because clearly the amount of seeds they need to make it work is not supported by the number of seeds that we have,” McMorrow says.
Planting trees from the sky is particularly attractive in areas that are hard for human crews to reach, and burned slopes are susceptible to erosion and mudslides. It has the potential to speed reforestation—one of humanity’s most effective weapons to combat climate change, according to the UN’s Intergovernmental Panel on Climate Change. The US Forest Service predicts that replanting on federal lands alone could reduce the nation’s carbon footprint by 14 percent. Globally, a group of scientists said in a 2019 paper that there was room on Earth to plant hundreds of billions of trees, which could reduce atmospheric carbon levels 25 percent.
Whether drones can help depends on how many of the drone-dropped seeds take root and grow into trees—which can be affected by factors such as flight path, the distribution of seeds, the speed with which they hit the ground, and whether they get eaten by squirrels or other wildlife.
“I’m sure there’s lots of people that have big ideas for drones,” says Robert McNitt, creator of the Forest Seedling Network, which maps seeds to certain areas in Idaho, Oregon, and Washington based on elevation and connects nurseries selling seedlings with small landowners. McNitt started planting trees in the 1950s. In the 1960s, he did some aerial seeding in Oregon that he characterized as unsuccessful. “It takes a lot of other steps beyond the scattering of seed to grow a forest, in my mind,” he says.
Not every drone-fired seed must take root for the method to be successful. According to Canadian startup Flash Forest, two drone pilots can scatter as many as 100,000 seeds a day. By comparison, a person working by hand can plant about 1,000 seedlings a day.
In a landmark study released this summer, researchers from more than a dozen government agencies, universities, and companies in seven countries conclude that drone seeding has the potential to restore forests and cool the planet, but low seed survival rates and other challenges stand in the way.
The researchers identified 10 tree-planting drone companies as well as university research in India and government reforestation efforts in New Zealand and Madagascar. In Myanmar, Thailand, and the United Arab Emirates, drones have been used to help plant mangrove trees, a potentially impactful development, since trees planted near the equator capture more carbon than those planted elsewhere.
But the researchers said few companies have shared success rates or research into how seeds fare after they’re dropped by a drone. They called on those involved in drone seeding to be more open about their results. They label pledges to grow a billion trees a year “propaganda.”
Mikey Mohan is a PhD candidate at UC Berkeley and lead author of the paper. He thinks commitments to grow a billion trees are largely promotional tactics by companies looking to raise funds from investors. He said half of the social media posts he saw pertaining to drones planting trees had to do with promises to plant a billion trees.
What actually matters is the number of seeds that grow into trees after two or three years, he said, not the number of seeds you can drop on the ground in a day.
The researchers cited a 2020 study by DroneSeed that found survival rates for some conifer tree seeds range between zero and 20 percent, similar to prior efforts to drop seeds from planes or helicopters in the US in the 1950s and 1960s. Like other companies in the field, DroneSeed declined to say how many trees it has planted to date. The company would not disclose the names of customers but says it is working with three of the five largest timber companies in the US, as well as nonprofit conservation groups such as the Nature Conservancy.
Last month, five-year-old DroneSeed acquired SilvaSeed, a 130-year-old company that’s one of the largest private forest seed providers on the US West Coast. For context, SilvaSeed grows more seedlings annually than the Cal Fire Reforestation Center. The acquisition was driven, DroneSeed CEO Grant Canary told WIRED, by the fact that Climate Action Reserve, which tracks the environmental benefits of emission-reduction projects, now includes benefits from reforestation.
“What we see with reforestation and carbon credits is now we're able to take land that’s been burned and make sure there’s a source of capital to reforest it,” Canary says.
In attempts to make seeds dropped by drones more viable, companies apply machine learning and imaging technology to pick optimal places to plant trees and guide drone flight paths. They encase seeds in pellets made with ingredients like clay and soil and sometimes shoot them into the ground. Each seed capsule is designed to contain the moisture and nutrients a seed needs to get started.
DroneSeed, for example, includes hot pepper to deter squirrels or other wildlife from eating its vessels, which are about the size of a hockey puck. How these carrying cases for seeds are made varies. Some contain a single seed, but Dendra Systems says it can pack up to 50 kinds of seeds for trees, shrubs, and native grass in a single capsule.
Asked to comment about the propaganda claim, Flash Forest CEO Bryce Jones said the company still plans to plant 1 billion trees by 2028.
Dendra Systems, previously known as Biocarbon Engineering, is one of the oldest and best-known companies using drones to plant trees. CEO Susan Graham said the company was created with the belief that a key reason humanity has yet to slow the decline in tree populations is that we aren’t using enough technology.
“You can solve the biodiversity challenge, you can solve the livelihoods challenge, and you can solve the carbon challenge all in one, if you can do it at scale,” she said.
She declines to say how many trees the company has planted. Ecologists are employed to verify results, she says, and the results of their work are shared privately with customers. She says Dendra now focuses more on the total area it can restore rather than the number of trees planted.
Former Dendra CEO Lauren Fletcher says he came up with the idea of using drones for planting trees in 2008, and he was one of the first CEOs to make the billion-tree pledge. He doesn’t think any drone-planting company has yet hit that target, but he thinks it remains worthwhile as an example of the big thinking needed to tackle global ecosystem restoration problems.
“The fact is people understand trees. They can see them, they can touch them, they can feel them, and it's a hell of a lot easier to sell,” he said. “Try selling soil microbes.”
Fletcher is currently working with Dendra Systems cofounder Irina Fedorenko on another company aiming to plant trees with small drones, particularly for small landowners. Through a partnership with WeRobotics, Flying Forests wants to plant trees with drones in 30 countries. It is exploring projects in Kenya, Panama, and Uganda.
In April, the company spread seeds on a hillside near Reno as part of a US Forest Service pilot program. Fletcher estimates 1 percent of those seedlings have started to grow. Despite low success rates, Fletcher argues that in areas where it’s tough for people to go or there’s a labor shortage, something is better than nothing.
A spokesperson told WIRED that the US Forest Service is considering using drones in post-fire recovery, particularly in areas that are difficult for people to reach, but that “survival and costs have not been optimal when compared with hand planting.”
Companies planting trees and government reforestation efforts will have to contend with ongoing seed shortages. A World Resources Institute study estimates that the US can grow 60 billion trees by 2040, but a study released earlier this year found that planting even half that many by 2040 would require federal nurseries to more than double their current output. Government forestry and conservation officials that authored the report highlighting gaps in the nation’s tree seed supply chain also call for more investment in seed collection and workforce training.
McMorrow, of Cal Fire, calls 2021 a good year for collecting cones that contain seeds, but he says wildfires and reforestation continue to outpace seed collection. Cal Fire is working with tribal governments and the US Forest Service to ramp up nursery production to double from 250,000 to half a million seedings. He suggests companies interested in drones and automation for planting trees invest resources in collecting seeds.
Updated, 9-28-21, 5:35pm ET: This story has been updated to include that DroneSeed has FAA approval to fly its drones beyond line of sight.