In a speech to the UN, the 16-year-old Swedish climate activist Greta Thunberg said, “The climate crisis has already been solved, we already have all the facts and solutions, all we have to do is wake up and change.” That is, staving off the crisis before us is as simple as cutting emissions and removing the excess greenhouse gases (GHGs) from our atmosphere. The currently best way to do the latter is to plant more trees – as many as a trillion more, for example, according to one estimate derived by Thomas Crowther and his colleagues at ETH University, Zurich.
Scientists and environmentalists understand this refers to a trillion mature trees. According to Crowther, Earth hosts about three trillion trees at any given point and that a trillion more could mean winning half the battle against climate change. However, the nuances of this recommendation have become diluted in numerous media reports to any kind of trees planted anywhere.
Pursuant to this, the governments of India and Ethiopia recently undertook large-scale afforestation but these attempts are unlikely to achieve the requisite level of carbon sequestration right away. In 2017, India planted 66 million saplings of fruit-bearing trees along the banks of the Narmada river. But fewer than “2% of the saplings survived,” according to Subash C. Pandey, an environmentalist at the GSEED foundation.
At a time when the climate emergency is becoming more impactful faster, plantation drives alone can do little to solve the problem our species faces. It takes years for trees to mature into the kind of ecological support system that promotes carbon sequestration at peak capacity. That politicians believe they can dawdle with PR exercises instead of ensure sincere reforestation only highlights their limited understanding of the crisis at hand.
Climate change mitigation involves working with all of Earth’s natural systems together at the same time, but this isn’t as hard as it sounds; it can be as simple as cutting emissions, maintaining existing forest cover and reforesting land that was previously forested. Regrowing a forest is, however, complicated. Humans are only beginning to understand how these ecosystems depend on biodiversity, along with other environmental factors. According to Pandey, “What one chooses to plant can [be different] every 50 km because the climate, soil composition and precipitation change based on geographic location.”
Trees photosynthesise the carbon they absorb from the atmosphere in a process that takes a lot more than water, sunlight and carbon to do well. All plants and trees require nutrients, depending on their specific needs; some minerals and nitrogen are absorbed from the soil and environment. The soil contains minerals because as a result of rock-weathering over several millennia. Since plants don’t extract minerals directly from weathered pieces of rock, they depend on there being water in the soil to soak up the powdered debris in a process called leaching, and roots then absorb the minerals from there.
In some cases, fungal colonies living inside the ground provide some nutrients that a plant’s roots might not be able to access. The fungi decompose and feed on organic matter in the soil, digesting the nutrients and convert them into something a plant can process. Nitrogen fixers convert atmospheric nitrogen into forms that trees can absorb. Roots barter with these fungi, offering carbon-based foods in exchange for water, nutrients and protection from disease-causing pathogens.
This relationship is called a mycorrhizal symbiosis – without it, plants wouldn’t have conquered land to the extent they have. So successful reforestation should be mindful of the presence of such collaborations. Apart from improving their supply of nutrients, mycorrhizal symbiosis helps them tolerate droughts and resist diseases better. According to Crowther’s lab at ETH Zurich, 80% of land plant species negotiate with Arbuscular mycorrhizae fungi while 60% of tree stems are associated with ectomycorrhizal fungi.
“Ectomycorrhizal symbiosis dominate forests in which seasonally cold and dry climates inhibit decomposition,” their peer-reviewed paper published in May this year states. “By contrast, Arbuscular mycorrhizal trees dominate in warm tropical forests with consistent weather and occur with ectomycorrhizal trees in temperate biomes in which seasonally warm-and-wet climates enhance decomposition.”
Mycorrhizal activity indicates soil health: the more there is, the fitter the plants and trees in the area are. Plant health also correlates with an increase in photosynthetic activity which, when together with decreased carbon loss from the soil, results in lesser quantities of carbon dioxide in the atmosphere. Newly planted saplings lack root and mycorrhizal length, so they will never be able to sequester as much carbon or contribute to soil health as mature trees.
Mono-cropping and the overuse of inorganic fertilisers has affected soil health. Poor soil health is responsible for roughly nine-times as much carbon in the atmosphere as human-made emissions. So promoting soil health is as essential to climate change mitigation as cutting industrial emissions and maintaining forest cover. It will be impossible to achieve our mitigation goals if we axe one for the other.
Nayomie Prasad Kapur is a climate and animal rights activist, entrepreneur and freelance journalist based in Mumbai.