Mapping Europe: drawing the forest map

The history of one of EFI’s most popular products, the Forest Map of Europe, goes back to the 1990s. At that point, there were several EU forest maps and also some satellite maps by the European Space Agency (ESA). While satellite data, in principle, provides a harmonized method of assessing forest cover over a large area, it often has drawbacks. Wooded land not fulfilling the definition of ‘forest’ is easily mis-classified as forest, and vice versa.

map_team_300.jpg : 95Kb Risto Päivinen takes up the story: “ For a Joint Research Centre project, we compared ESA forest cover and national inventory statistics and observed up to 20–30% differences in some countries. The challenge was to prepare a map where these differences did not appear. The basis of the Forest Map of Europe is a model resulting in the scaling of the forest cover unit-% within every one kilometre NOAAAVHRR satellite pixel. Working with VTT, Finland and the University of Eastern Finland, the key was an iterative calibration algorithm we developed at EFI to get the sum of forest cover counted from the pixels, to match with forest area for a region or a country, as derived by field inventory.”

This algorithm typically provided an almost 100% match between the regional statistics and the sum of forest in the pixels within a regional boundary. Additional data, such as knowledge of the tree line in the mountains was used to exclude forest which appeared mistakenly in the satellite maps at high altitudes. In the final result, the correct amount of forest was on the map of calibration area, but mistakes may still appear in the location of forest within that particular area. The smaller the calibration areas used, the more accurate the overall map turned out to be.

With the forest area map as a basis, it was fairly easy to embed other information in the basic map. Tree species, standing volume, forest carbon and forest ownership maps have been prepared and used in spatial analysis for various projects.

“An image says more than a thousand words, which is why maps continue to be such an attractive way of giving a quick visualization of the state of the European forests.”
Risto Päivinen