Carbon Sequestration Through Avenue and Median Plantation

Every highway project in India now carries a green component. Under the Green Highways Policy 2015, the Ministry of Road Transport and Highways set aside 1% of highway project costs for plantation and its upkeep. Done well, avenue trees and median planting become one of the few parts of a road that actively take carbon out of the air. Done badly, they die within two summers and store almost nothing.

How trees store carbon

Trees take in carbon dioxide as they grow and lock the carbon into wood, roots and leaves. Roughly half of a tree's dry weight is carbon, and every tonne of stored carbon equals about 3.67 tonnes of CO₂ removed from the atmosphere, the ratio of their molecular weights. So the carbon a plantation stores depends mainly on how much wood it grows. That depends on species, growth rate and lifespan, and above all on whether the plants survive.

Avenue trees and median shrubs do different jobs

Avenue plantation, the rows of trees along the edges of a road, does most of the carbon work. A large, long-lived tree keeps adding wood for decades. Medians are different. They are usually planted with shrubs kept low enough to block headlight glare without hiding traffic, so their woody biomass stays small. Medians still matter, but mainly for other reasons.

• Avenue rows: large, long-lived trees. The highest carbon storage, plus shade for pedestrians and cyclists.
• Medians: dense, low shrubs. Modest carbon storage; the main benefits are glare reduction, dust capture and appearance.
• Green belts beyond the road edge: multi-row planting where land allows, combining tall trees and shrubs for both carbon and screening.

Species that work in north India

For avenue rows, native and naturalised trees that tolerate heat, dust and dry spells perform best. Neem, peepal, pilkhan, arjun, jamun, amaltas and kachnar are common choices. Fig species such as peepal and pilkhan grow large and live long, which makes them strong carbon stores. For medians, hardy shrubs such as kaner (oleander) and bougainvillea are widely used because they cope with pollution, heat and limited watering.

Mix species rather than planting one along an entire stretch, so a single pest or disease can't wipe out the plantation. Spacing and setbacks follow the project specifications and road safety rules: trees must not block sight lines at junctions or crowd utilities.

Estimating the carbon a plantation stores

Credible estimates come from measurements, not per-tree rules of thumb. The usual method is:

1. Measure each tree's trunk diameter at breast height (1.3 m) and, ideally, its height.
2. Apply a published allometric equation for the species or forest type to estimate above-ground dry biomass.
3. Add below-ground (root) biomass, usually estimated as a fraction of the above-ground figure.
4. Multiply total dry biomass by the carbon fraction (about 0.47, the IPCC default) to get stored carbon.
5. Multiply the carbon by 3.67 to express it as CO₂.

Repeat the measurements every year or two, and the difference is the carbon sequestered over that period. Treat headline "kilograms per tree per year" figures with caution: young roadside trees store very little in their first years, and real values vary widely by species and site.

A dead sapling stores no carbon. On most roadside plantations, survival matters more than the number of saplings planted.

What decides survival

Roadside plants face heat, dust, vehicle damage, grazing animals and irregular watering. The plantations that survive have a few things in common:

• Larger, nursery-hardened saplings rather than small seedlings.
• Tree guards against animals and vehicles.
• Reliable watering through the first two to three summers, ideally drip lines along medians and avenue rows.
• Prompt replacement of failed plants, written into the maintenance contract.
• Mature tree transplantation instead of felling when a road is widened. An existing large tree already holds decades of stored carbon that a new sapling would take decades to replace.

Carbon credits and green credits

Plantation projects can earn carbon credits under international standards such as Verra's Verified Carbon Standard or Gold Standard. Credits require baseline studies, long-term monitoring and third-party verification, so they are usually practical only for large or aggregated projects. In India, the Ministry of Environment, Forest and Climate Change launched the Green Credit Programme in 2023, and tree plantation is one of the activities it covers. If credits are part of the plan, design the monitoring from day one.

From our work

We planted 3,500 hardy, pollution-tolerant plants on the NH-7 median for an NHAI contractor. On NH-307 we relocated 155 mature trees instead of felling them during road widening. See our plantation and transplantation services.