The Social Life of Forests

The Social Life of Forests

Trees appear to communicate and cooperate through subterranean networks of fungi. What are they sharing with one another?

By Ferris Jabr
Photographs by Brendan George Ko

As a child, Suzanne Simard often roamed Canada’s old-growth forests with her siblings, building forts from fallen branches, foraging mushrooms and huckleberries and occasionally eating handfuls of dirt (she liked the taste). Her grandfather and uncles, meanwhile, worked nearby as horse loggers, using low-impact methods to selectively harvest cedar, Douglas fir and white pine. They took so few trees that Simard never noticed much of a difference. The forest seemed ageless and infinite, pillared with conifers, jeweled with raindrops and brimming with ferns and fairy bells. She experienced it as “nature in the raw” — a mythic realm, perfect as it was. When she began attending the University of British Columbia, she was elated to discover forestry: an entire field of science devoted to her beloved domain. It seemed like the natural choice.

By the time she was in grad school at Oregon State University, however, Simard understood that commercial clearcutting had largely superseded the sustainable logging practices of the past. Loggers were replacing diverse forests with homogeneous plantations, evenly spaced in upturned soil stripped of most underbrush. Without any competitors, the thinking went, the newly planted trees would thrive. Instead, they were frequently more vulnerable to disease and climatic stress than trees in old-growth forests. In particular, Simard noticed that up to 10 percent of newly planted Douglas fir were likely to get sick and die whenever nearby aspen, paper birch and cottonwood were removed. The reasons were unclear. The planted saplings had plenty of space, and they received more light and water than trees in old, dense forests. So why were they so frail?

Simard suspected that the answer was buried in the soil. Underground, trees and fungi form partnerships known as mycorrhizas: Threadlike fungi envelop and fuse with tree roots, helping them extract water and nutrients like phosphorus and nitrogen in exchange for some of the carbon-rich sugars the trees make through photosynthesis. Research had demonstrated that mycorrhizas also connected plants to one another and that these associations might be ecologically important, but most scientists had studied them in greenhouses and laboratories, not in the wild. For her doctoral thesis, Simard decided to investigate fungal links between Douglas fir and paper birch in the forests of British Columbia. Apart from her supervisor, she didn’t receive much encouragement from her mostly male peers. “The old foresters were like, Why don’t you just study growth and yield?” Simard told me. “I was more interested in how these plants interact. They thought it was all very girlie.”

Now a professor of forest ecology at the University of British Columbia, Simard, who is 60, has studied webs of root and fungi in the Arctic, temperate and coastal forests of North America for nearly three decades. Her initial inklings about the importance of mycorrhizal networks were prescient, inspiring whole new lines

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Dendra System’s seed-spitting drones rebuild forests from the air

There is hope, however. A recent study in the journal Nature found that “restoring 15 percent of converted lands in priority areas could avoid 60 percent of expected extinctions while sequestering 299 gigatonnes of CO2.” That’s a third of the total increase of atmospheric carbon dioxide since the start of the Industrial Revolution. 

In response, governments, NGOs, charities and even private businesses have devised and implemented reforestation plans that work much like the “take-a-penny, leave-a-penny” trays next to your bodega’s cash register do. Essentially they seek to replace what has been removed in order to maintain balance within the system. In 2011, for example, Germany and the International Union for Conservation of Nature launched the Bonn Challenge which seeks to restore 350 million hectares (Mha) of land by 2030. To date, more than 43 nations located in tropical and subtropical climates have pledged to restore 300 Mha. 

These are lofty goals indeed. The problem is, reforestation efforts are labor intensive. You need boots on the ground and hands in the soil for these campaigns to be successful and, as such, often become long, slogging affairs. For example, the Worldview International Foundation in 2012, launched a campaign to plant a billion mangrove trees in the nation of Myanmar. In the subsequent seven years, local volunteers managed to plant 6 million seedlings by hand — an admirable effort but simply too slow to make a difference at the scale required. That’s when Dendra Systems, a drone-based forest restoration company, got involved. With the help of modern avionics and automation, the campaign managed to plant an additional 4 million mangrove seedlings in 2019 alone. The company estimates that a pair of operators flying ten drones could plant as many as 400,000 trees per day.

“The human species has been very good at building tools to do deforestation at an industrial scale,” Jeremie Leonard, an engineer with Dendra Systems, told Engadget. “And, for a long time, the state of the arts in ecosystem restoration was hand planting. So we’re trying to give restoration a toolset to be able to do that at the largest scale.”

For Dendra, that toolset includes two types of modified commercial-grade autonomous aerial drone platforms, a visual AI, a machine learning algorithm for establishing seeding patterns, and a custom built seed-spitter that fires marble-sized pods packed with baby trees and all the nutrients they need to get growing. Since the company’s founding in 2014, it has completed nearly 40 contracts in 11 nations, largely working with resource extraction companies to repair landscapes after the completion of mining and forestry activity.

The company’s fourfold restoration process starts with an in-depth aerial survey of the acreage to be reclaimed, looking at “the terrain, the topology, the nutrients, the biodiversity,” founder Lauren Fletcher said during a 2017 Ted Talk, as well as slope, soil type and moisture. Dendra’s largest mapping drone can carry up to 22 kilograms of equipment and its sensors can resolve images at 2-3cm per pixel. “The idea of going

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Regenerated forests offset 12% of carbon emissions in Brazilian Amazon in 33 years

Regenerated forests offset 12% of carbon emissions in Brazilian Amazon in 33 years
A study quantified the size and age of the forests that grow naturally in degraded and abandoned areas, creating 131 benchmark maps for Brazil. The Amazon has the most restored forests and the Atlantic Rainforest biome has the oldest Credit: Tropical Ecosystems and Environmental Sciences Laboratory – INPE

Secondary forests play an important part in carbon capture because they tend to absorb a larger amount of carbon than they lose to the atmosphere. However, the size and average age of these often abandoned areas where vegetation grows back were unknown until now. In a study recently published in the journal Scientific Data, a group led by two researchers at Brazil’s National Institute for Space Research (INPE) quantified these variables and found that the estimated carbon uptake by secondary forests throughout Brazil offset 12% of the carbon emissions due to deforestation in the Brazilian Amazon alone in a 33-year period.

The study was supported by FAPESP via two projects. The first project began in 2017 and is led by Luciana Vanni Gatti. The second began in 2019 and is led by Luiz Eduardo Oliveira e Cruz de Aragão.

“The capacity of secondary forests to absorb carbon is known from studies that involve monitoring of areas in the field. Their average net carbon uptake rate in Neotropical regions is 11 times that of old-growth forests. However, the long-term dynamics of secondary forests in Brazil and worldwide is poorly understood,” said Aragão, one of the authors of the study, which was conducted at INPE as part of Celso H. L Silva Júnior’s Ph.D. research.

This knowledge is fundamental to enable Brazil to achieve its Nationally Determined Contribution targets under the 2015 Paris Agreement. These include the restoration and reforestation of 12 million hectares of forest by 2030, he noted.

Age and size of secondary forests in each biome

The study calculated the increment in secondary forests that previously had anthropic cover (plantation, pasture, urban infrastructure, or mining) and their age, biome by biome. According to Aragão, secondary forest growth is not linear and correlates with age, so that it is important to establish the age of a forest in order to estimate its carbon uptake.

The data showed that a total of 262,791 square kilometers (km²) of secondary forests were recovered in Brazil between 1986 and 2018. This corresponds to 59% of the old-growth forest area cleared in the Brazilian Amazon between 1988 and 2019.

“The restored forests were located all over Brazil with the smallest proportion in the Pantanal [wetlands in the Center-West], accounting for 0.43% [1,120 km²] of the total mapped area. The largest proportion was in the Amazon, with 56.61% [148,764 km²]. The Caatinga [the semi-arid biome in the Northeast] accounted for 2.32% [6,106 km²] of the total area and had the youngest secondary forests—over 50% were between one and six years old,” Aragão said.

The Atlantic Rainforest ranked second by size of restored areas, with 70,218 km² (or 26.72% of the total), and had the oldest—over half were

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