Tree planting has become one of the most recognizable symbols of climate action — visible, easy to measure, and straightforward to communicate. But scientists are warning that indiscriminate tree planting, particularly in natural grasslands, shrublands and savannas, can do more harm than good, threatening biodiversity, reducing water availability and undermining the very climate goals it is meant to serve.
The concern is timely. Global restoration initiatives operate at enormous scale, including the Bonn Challenge, which aims to restore 350 million hectares of degraded and deforested land by 2030. The African Union’s Great Green Wall Initiative, launched in 2007 to halt the southward expansion of the Sahara by planting trees across 22 countries, has produced mixed results after nearly two decades. The problem, researchers say, is a fundamental misclassification of what counts as degraded land. Drylands — which include grasslands, shrublands and savannas — cover roughly 40 percent of Earth’s surface and support billions of people. Their sparse vegetation is not a sign of ecological failure; it is the product of millions of years of adaptation to low rainfall, recurrent drought and periodic disturbance. Treating these landscapes as candidates for tree cover risks replacing one functioning ecosystem with another.
The ecological consequences of misplaced tree planting are well documented. Trees consume water, and large-scale forestation in water-limited environments can significantly reduce river flow, lower groundwater levels and threaten downstream farming and household water security. There is also a biophysical effect that carbon accounting often overlooks: open vegetation and light-coloured soils reflect more sunlight than a dark tree canopy. Converting dryland to forest lowers an area’s albedo — the measure of sunlight reflected — meaning more solar energy is absorbed. Research shows this effect can offset a substantial portion of the climate benefit that tree planting is supposed to deliver.
Researchers point to approaches that work with dryland ecosystems rather than against them. In Niger, farmer-managed natural regeneration — protecting and managing native trees and shrubs that regrow from existing roots and stumps — helped regreen approximately five million hectares without mass seedling campaigns. In Burkina Faso, farmers have revived an ancient technique called zaï, using planting pits that collect runoff and concentrate organic matter around crops, rehabilitating degraded land under difficult rainfall conditions. Both approaches define restoration by the recovery of soil function, vegetation and livelihoods, not by how closely a landscape resembles a forest.
The broader lesson, according to researchers, is that governments and donors need to ask different questions before funding restoration projects: Does a project restore the natural ecosystem? Does it protect water? Does it retain native biodiversity? Tree planting has genuine value in deforested areas where the right species, adequate water and secure land tenure align — but that success should not be treated as a universal template. Drylands are not failed landscapes waiting to be forested. They are distinct, functional ecosystems, and restoring them means supporting the life already adapted to thrive there.