Humans cutting 15 billion trees per year
How many trees are on the planet? That's not an easy question to answer. Nobody's going to go out and count them one by one, so other methods must be devised to get decent estimates. Until recently, the best number we had was around 400 billion, which any way you slice it is a lot of trees. But that was apparently undershooting by a wide margin. The latest estimate, which is based on mass of ground survey data and satellite pictures compiled by researchers at Yale University, is closer to 3 trillion trees, or about 7.5x more than we thought. Of these trees, approximately 1.39 trillion are located in tropical and subtropical forests, 0.74 trillion in boreal regions, and 0.61 trillion in temperate regions.
This is an important number because it'll be used in all kinds of other research, such as climate models, studies on animal and plant habitats and biodiversity, etc. But be careful, the trees are not "new", they were there before even if we were undercounting them:
But Dr Crowther cautioned that the higher number did not of itself change anything.
He told the BBC's Science In Action programme: "It's not like we've discovered a load of new trees; it's not like we've discovered a load of new carbon.
"So, it's not good news for the world or bad news that we've produced this new number. We're simply describing the state of the global forest system in numbers that people can understand and that scientists can use, and that environmental practitioners or policymakers can understand and use." (source)
The Yale scientists estimate that humans are removing about 15 billion trees each year, and planting back around 5 billion.
Since the last ice age about 11,000 years ago, humans are estimated to have removed about 3 trillion trees, or about half of the total at the time. "Europe used to be almost covered by one giant forest and now it's almost entirely fields and grasslands. Humans are absolutely controlling tree densities," Dr Crowther told BBC News.