Million-tree mission hopes to fix reforestation flaws

Former schoolteacher Vanhanen has overseen the planting of 30 million trees across the globe via a network of 10,000 schools he recruited over two decades. Photo: AFP

It's an environmental policy embraced by heads of state, multinational businesses and even leading climate sceptic Donald Trump: plant more trees to help the planet and slow global warming.

But experts claim some recent mass tree-planting schemes have failed to reduce greenhouse gases when not done properly, and even harmed the environment.