USGS has published tree cover data based on 2010 Landsat captures. I wonder if this data would be suitable for importing. Especially outside of Europe, forest cover is largely incomplete now, and 2010 is fairly recent for this kind of data.
In the licence requirement it says: University of Maryland, Department of Geographical Sciences and USGS; use is free to all if acknowledgement is made. So it is not obvious if using this data is allowed.
The data is provided asgreyscale geoTIFFs, i have uploaded one tile as a preview here:
Is the licence ok to use for adding data to OSM? If not, we could seek explicit permission from USGS, this data was directly derived from Landsat anyway, so they may be able to allow less strict attribution requirements.
Should the licence be suitable, then of course there will be many issues. For starters, the data is about 'tree cover' which could be 'landuse=forest', 'natural=wood', 'landuse=orchard', etc. Then there is the difference between OSM, where an area can only be forest or not forest, and this 1-100 scaled data. At which threshold is it a wooded area?