It is a big feat to estimate the number of trees on Earth! Satellite images can tell you a lot about the forest area and canopy cover, but they cannot see individual trees. In 2005, one group converted that coverage into a measurement known as tree density and concluded the planet was home to 400 billion trees, or 60 trees per person.
Scientists at the Yale School of Forestry and Environmental Studies undertook a study a few years ago, where they gathered over 425,000 ground-sampled estimates of tree density from more than 50 different countries. Other estimates came from established scientific organizations, such as the Smithsonian Tropical Research Institute, and still others came from peer-reviewed studies published in the last ten years. Researchers used satellite imagery and assessed how the data was related to local factors like climate, human activity and soil conditions, and used the information to build a global model. Researchers visited each and every site where they counted, measured and qualified trees within a one-hectare field plot. These plot data provided a concrete way to strengthen information obtained from satellites.
The hypothesis is that the combination of datasets can accurately capture the changes in tree density across the Earth, and analyzing those relationships, one can predict tree density at locations that were not directly measured. The central theme of the new
study was to develop relationships between the different datasets and the estimates of tree density that came from ground-sampled field plots. The new study revealed that there are approximately 3 trillion trees in the world, an entire order of magnitude greater than the previous estimate of 400 billion. For each person on Earth there are 422 trees. It is estimated that humans cause a net loss of around 10 billion trees annually based on 5 billion planted and 15 billion removed. The global number of trees has fallen by about 46% since the start of modern human civilization around 12,000 years ago.
Trees store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality!!