How many trees are there in the world?  Four hundred billion was the figure often quoted; that is, until this month when a report in Nature has come up with a figure slightly in excess of three trillion.   This approximates to 420 trees for each person on the plant.

How was this figures arrived at ?  Well, the team (an impressive array of scientists from Universities and research institutions all over the world) amassed data from national forest inventories, plus peer reviewed studies where forests and woodlands had been studied in detail; this information was then used to inform what was also being seen on satellite imagery. For the purposes of the study a tree was defined as "a plant with a woody stems larger than 10 cm at breast height". 

So, of the 3,040,000,000,000 trees some 1.39 trillion were in the tropics and sub-tropics, 0.61 trillion in temperate regions and 0.74 trillion in the Arctic and sub-arctic coniferous forest - the Boreal Forest.   Tree density is probably greatest in the Boreal Forest / Arctic regions.

Sadly, trees are being removed, cut down faster than they are being replaced.   The report suggests a removal rate of (circa) 15 billion trees per year, and a replacement rate of 5 billion a year.   These figures  should "...give us cause for considering the role that deforestation is playing in changing ecosystem" to quote Dr H B Glick (one of the authors from Yale School of Forestry and Environmental Studies).   Tree removal and deforestation has been a feature of human activity for the last eleven thousand years (since the last Ice Age), perhaps accounting for the removal of some three trillion trees.  It is estimated that the global total of trees has fallen by 46% since the onset of 'human civilisation'.  At one point, most of Europe and Asia was covered in trees but much is now fields and grassland.