Trees can help fight climate change — but what about their problems?

“Trees are behaving differently across the world,” Geetha Ramaswami of the Nature Conservation Foundation (NCF) said. Ramaswami is the team lead of SeasonWatch, a citizen science project that monitors tree phenology — the timing of flowering, fruiting, and leafing — across India. “We’re seeing them flower earlier, leaf earlier, and even shift their geographic range.”

The iconic Indian laburnum (Cassia fistula), called “amaltas” in northern India and “kanikonna” in the south, has been flowering earlier than usual. Cassia is native to India and is the State tree of Kerala and Delhi. It makes for a majestic sight, with its bright yellow flowers dangling like droplets of gold above a wide, sturdy trunk.

Traditionally, the Indian laburnum tree has been a kind of “climate clock” for the people of Kerala, with its blossoms marking Vishu, the Malayali new year, celebrated around April 14 or 15. But according to SeasonWatch’s observations over the last few years, the trees’ flowers have been blooming earlier than usual, leaving many people scrambling for plastic replacements during the festival to decorate their houses, Ramaswami said.

As climate change picks up pace, trees are often hailed as frontline defenders — natural carbon sinks that combat rising emissions. But trees themselves are changing in response to a warming world: they’re flowering earlier, migrating uphill, competing with other trees for resources, and sometimes failing to survive in new conditions. Even as governments and corporations push mass afforestation as a solution, ecologists are warning that poorly planned tree-planting efforts will only worsen ecological imbalances.

In this chapter, let’s explore how climate change is affecting tree behaviour, why our understanding of trees in climate strategies needs to evolve, and what truly sustainable, place-based restoration looks like.

Warriors in distress

Countries and corporations across the world are championing afforestation drives, often under Corporate Social Responsibility (or CSR) mandates or climate pledges, using trees as a solution to sequester carbon. This enthusiasm, according to several ecologists, is misplaced or misguided.

“Tree planting has become an industry,” Sanjay Molur of the Zoo Outreach Organisation and who works on ecological restoration in Himachal Pradesh, said. “States boast of planting 10 million trees, but don’t ask whether they are the right trees or whether they are planted in the right place.”

Large-scale afforestation is not new to India. For instance, in 2019, Uttar Pradesh planted 220 million trees in a single day as part of a massive afforestation drive. But researchers soon said that the choice of species and planting locations often lacked ecological considerations.

Trees are living beings and compete with humans for the common and limited freshwater resources. Non-native species like eucalyptus, jacaranda, and gulmohar are often favored for their rapid growth and aesthetic appeal but they are water-guzzlers. Some eucalyptus species have been known to extract more than 90 liters of water per day from the soil. Commercially valuable species like teak, often grown in plantations, can rapidly deplete the local water table and alter soil chemistry, rendering the land unsuitable for native flora.

“We humans think that growing more trees will sequester more carbon, but that can have a negative impact on the water balance of the soil,” Ganesan Rengaian, a botanist and ecologist at the Ashoka Trust for Research in Ecology and the Environment (ATREE) in Bengaluru, said. “We are competing for a common resource — groundwater — and of course we humans have the edge in that competition.”

Molur, who has assessed multiple conservation and afforestation projects, said, “Most of [the trees] are non-native invasive species that have been replanted from elsewhere. And these are thousands of saplings in an acre.” These plantations often prioritise economically valuable trees like timber and fruit-bearing species, which, while beneficial in the short term, may not support local biodiversity or long-term ecological balance in the long term.

Companies claim to sequester many tonnes of carbon using plantations as a tool whereas the planted species here are high-value flora and not known for sequestering carbon. “These are being done by local people. And at the end of it, the local people want to harvest it. When you harvest or cut down a tree, you’re putting carbon back into the atmosphere. … The tree is not sequestering any carbon,” Molur said.

Such non-native species have come to dominate many landscapes, suppressing native vegetation and reducing biodiversity. “Humans are more tuned towards more economically important trees, whether it is timber, fruit, or oil-yielding trees,” Rengaian said. “We don’t think of trees as habitats or about the other natural services that they provide. At present, we are thinking more about how much carbon credit we can get. Which plant species will give more carbon credit and which tree will grow much faster and then will fix more carbon?”

He suggested that before deciding on what tree to plant, “we have to think about what kind of habitat we are going to replace with these trees and [how much nutrients and water] these trees demand and how they are going to recycle these nutrients and water into the same system.”

Big tree, big carbon?

“People assume the bigger the tree, the more carbon it sequesters,” Molur said. “But it’s not that linear.”

A 2019 study in Global Change Biology found that monoculture plantations store significantly less carbon and support far less biodiversity than natural forests. In contrast, native, mixed-species forests create resilient ecosystems that support fungi, birds, mammals, and soil microbes, enhancing long-term carbon storage and ecological health.

India’s history with forests is also misunderstood. “India was never a forested country in totality,” Molur said. “Sixty percent of our land was historically grassland, scrubland or open woodland.” Yet afforestation efforts often aim to “green” these open ecosystems, treating them as ‘badlands’ that can be ‘improved’ by planting trees.

Across India, many lawmakers, policymakers, and civil society organisations are rooting to afforest native grasslands under afforestation and climate-change mitigation schemes. These open ecosystems — labeled “wastelands” in official maps — are being planted over with non-native and often fast-growing tree species such as eucalyptus, acacia, and Prosopis. This is especially visible in regions like the Western Ghats, Central India’s plateaus, and the arid zones of Rajasthan. In almost all these places, tree plantations are replacing ecologically rich grasslands.

Such interventions often disregard the unique biodiversity grasslands support, including endangered species like the great Indian bustard, blackbucks, and several endemic butterflies and grasses. Experts have warned that this green cover expansion risks destroying habitats instead of preserving them, and worsening the consequences of climate change.

Contrary to popular belief, grasslands can be as effective — or even superior — to forests at sequestering carbon, especially in the long term. Unlike forests, which store most of their carbon in above-ground biomass, grasslands store the majority of their carbon underground in deep, resilient root systems. A 2022 study published in Science estimated that grasslands store up to 34% of the world’s terrestrial carbon, with a greater proportion remaining trapped even during disturbances like fires or droughts. Because this underground carbon is less likely to be released, grasslands offer a more stable and durable carbon sink, particularly in semi-arid and fire-prone regions.

However, as Trisa Bhattacharjee of the Zoo Outreach Organisation noted, grasses don’t offer the kind of optics or quick returns that funders or corporate donors are often looking for.

Trees v. climate change

Trees have come to symbolise hope in the fight against climate change. They are often romanticised as “green warriors” that can pull carbon out of the air and cool a ceaselessly warming planet. But they are feeling the heat as well.

“Trees are climbing the mountains,” Ramaswami of the NCF said. “They’re dispersing further uphill. Their density, regeneration, and distribution are all being affected.”

That is to say, trees are shifting, adapting, shrinking, and in some cases dying. Like humans, their resilience depends on complex support systems, including stable ecosystems, healthy soils, clean water, and the considerate actions of their fellow lifeforms.

Planting trees is in and of itself not a bad idea. But real climate action requires more than mass plantation drives. “It’s about planting the right trees, in the right place, for the right reasons, and with the right people,” Ramaswami said. “Unfortunately, many trees planted in cities or along highways are exotic species, chosen for their aesthetics or growth rate. In doing so, we have fundamentally altered what kinds of trees are found where, and often at the cost of local biodiversity.”

One major challenge is that the consequences of climate change on trees themselves remain under-researched. SeasonWatch, the citizen science initiative that Ramaswami leads, is one of a few efforts trying to bridge this gap. And they also face challenges of their own in their work. “We get less data from northern India,” she said. “So we still have big blind spots in understanding how trees across different regions are responding to a changing climate.”

According to all the experts interviewed, a responsible response to the climate crisis demands a deeper shift: in policies as well as in our ecological mindset and on-the-ground practices.

Rengaian of ATREE said that the crisis is not only about rising temperatures or carbon levels but also about the very fabric of our ecosystems. “When we promote afforestation indiscriminately, without understanding the local ecology or needs of the land, we risk doing more harm than good,” he said.

All experts also suggested resisting the hubris of engineering nature with blanket solutions. “A responsible response to climate change isn’t just about planting more trees,” Rengaian added.

In sum, it’s about understanding which tree, where, and why. It’s not just about carbon storage but about restoring the relationships between humans and ecosystems. And it’s not about short-term optics but about long-term resilience.

Monika Mondal is a freelance science and environment journalist.