Tree planting campaigns are increasingly promoted as a climate solution but large scale planting in drylands can damage ecosystems, reduce water availability and threaten local livelihoods, according to an analysis.
The article argues that landscapes without dense tree cover are not necessarily degraded. Grasslands, shrublands and savannas have evolved under conditions of low and variable rainfall, drought and periodic disturbance. Replacing these naturally open ecosystems with forests can therefore cause ecological damage rather than restore them.
Global restoration programmes have set ambitious targets for increasing vegetation cover. The Bonn Challenge, for instance, aims to restore 350 million hectares of degraded and deforested land by 2030. Africa’s Great Green Wall Initiative launched in 2007 to combat desertification across the Sahel, has also promoted landscape restoration across 22 countries.
However, the article notes that such programmes have produced mixed results and argues that restoration efforts need to be tailored to individual ecosystems rather than relying on tree planting as a universal approach.
One concern is water availability. Trees require water, and planting species that are poorly suited to dry environments can reduce the amount of water reaching rivers and streams. Changes in groundwater levels and downstream water availability can affect ecosystems, agriculture and household water supplies.
The climate impact of converting open landscapes into forests also extends beyond carbon storage. Grasslands and other open ecosystems can reflect more sunlight than darker tree canopies. Increasing tree cover can therefore reduce surface reflectivity, or albedo and increase the amount of solar energy absorbed by the land.
The article highlights several restoration approaches that can be better suited to drylands. In Niger, farmer managed natural regeneration has helped restore native trees and shrubs from existing roots, stumps and seeds across millions of hectares. The approach allows farmers to select and manage species according to local agricultural and livelihood needs.
In Burkina Faso, farmers have revived the traditional zaï technique in which planting pits collect rainwater and concentrate organic matter around crops. Such soil and water conservation practices can improve soil function and agricultural productivity under difficult rainfall conditions.
Other restoration measures can include protecting native grasslands, managing grazing pressure controlling invasive species, conserving biological soil crusts and supporting the natural recovery of locally adapted vegetation.
The analysis concludes that tree planting can play an important role where forests have been degraded or cleared and where suitable species, water availability and long term land management conditions exist. However, restoration policies should focus on recovering ecosystem functions, protecting water resources and conserving native biodiversity rather than simply increasing tree numbers.