Zach St. George writes: Gregor Hintler had what seemed like a simple question: How many trees are there? As part of Plant for the Planet, a youth initiative that aimed to plant one billion trees in every country by 2020, he needed a way to figure out how many trees the planet could fit. But when he tried to find out, he realized nobody knew the answer. One estimate suggested 400 billion trees. “That sounds like a lot,” he recalls thinking. “Could be right.” But Hintler, who was then a graduate student in environmental management at Yale University, started looking at data from plots in Germany, Norway, and the United States, where foresters had counted the number of trees. He discovered that the old figures weren’t even close — 400 billion was, in fact, far too low.

Forests cover about one third of the planet’s terrestrial area. They prevent desertification and erosion, store carbon, and provide habitat for millions of species. The recent Paris climate agreement highlights their importance, recommending that signing countries take steps to slow deforestation and enlist their forests in carbon credit markets. Knowing how many trees there are now, and how many there used to be, will help researchers assess human impact on the planet and any options going forward. [Continue reading…]