They use a technique of comparing energy use to countries. So I figured we could try this. Now, this is just an example, but I think the strategy is what's important. Iceland has 1906 km2 of forest. Basically it's all one type of forest, so we can pretty accurately determine how many trees they have. According to ourworldindataDOTorg, there's 6511 trees per km2. So there is 12,409,906 in Iceland.
