This data set measures areas of tree cover loss across all global land (except Antarctica and other Arctic islands) at approximately 30 × 30 meter resolution. The data were generated using multispectral satellite imagery from the Landsat 7 thematic mapper plus (ETM+), and Landsat 7 thematic mapper plus (ETM+), and Landsat 8 Operational Land Imager (OLI) sensors. Over 1 million satellite images were processed and analyzed, including over 600,000 Landsat 7 images for the 2000-2012 interval, and approximately 400,000 Landsat 5, 7 and 8 images for the 2010-2013 interval. The clear land surface observations in the satellite images were assembled and a supervised learning algorithm was applied to identify per pixel tree cover loss.
Tree cover loss is defined as “stand replacement disturbance,” or the complete removal of tree cover canopy at the Landsat pixel scale. Tree cover loss may be the result of human activities, including forestry practices such as timber harvesting or deforestation (the conversion of natural forest to other land uses), as well as natural causes such as disease or storm damage. Fire is another widespread cause of tree cover loss, and can be either natural or human-induced.
2015 Update (Version 1.1)
This data set was recently updated and now includes a 2013 loss layer and revised layers for 2011 and 2012. The analysis method has been modified in numerous ways, and the update should be seen as part of a transition to a future “version 2.0” of this data set that is more consistent over the entire 2001 and onward period. Key changes include:
- The use of Landsat 8 data for 2013 and Landsat 5 data for 2010-2011
- The reprocessing of data from 2011 to 2012 in measuring loss
- Improved training data for calibrating the loss model
- Improved per sensor quality assessment models to filter input data
- Improved input spectral features for building and applying the loss model
These changes lead to a different and improved detection of global tree cover loss. However, the years preceding 2011 have not yet been reprocessed with the revised analysis methods, and users will notice inconsistencies between versions 1.0 (2001-2012) and 1.1 (2001-2013) as a result. It must also be noted that a full validation of the results incorporating Landsat 8 has not been undertaken. Such an analysis may reveal a more sensitive ability to detect and map forest disturbance using Landsat 8 data. If this is the case then there will be a more fundamental limitation to the consistency of this data set before and after the inclusion of Landsat 8 data. Validation of Landsat 8-incorporated loss detection is planned.
Some examples of improved change detection in the 2011–2013 update include the following:
- Improved detection of boreal forest loss due to fire
- Improved detection of smallholder rotation agricultural clearing in dry and humid tropical forests
- Improved detection of selective logging
These are examples of dynamics that may be differentially mapped over the 2001-2013 period in Version 1.1. A version 2.0 reprocessing of the 2001 and onward record is planned, but no delivery date is yet confirmed.
The original version 1.0 data remains available for download here.
Citation: Hansen, M. C., P. V. Potapov, R. Moore, M. Hancher, S. A. Turubanova, A. Tyukavina, D. Thau, S. V. Stehman, S. J. Goetz, T. R. Loveland, A. Kommareddy, A. Egorov, L. Chini, C. O. Justice, and J. R. G. Townshend. 2013. “High-Resolution Global Maps of 21st-Century Forest Cover Change.” Science 342 (15 November): 850–53. Data available online from: http://earthenginepartners.appspot.com/science-2013-global-forest.
Suggested citations for data as displayed on GFW:Hansen, M. C., P. V. Potapov, R. Moore, M. Hancher, S. A. Turubanova, A. Tyukavina, D. Thau, S. V. Stehman, S. J. Goetz, T. R. Loveland, A. Kommareddy, A. Egorov, L. Chini, C. O. Justice, and J. R. G. Townshend. 2013. “Hansen/UMD/Google/USGS/NASA Tree Cover Loss and Gain Area.” University of Maryland, Google, USGS, and NASA. Accessed through Global Forest Watch on [date]. incendios.fan-bo.orf.