OPEN DEVELOPMENT CAMBODIA
FOREST COVER
DESCRIPTION
ODC’s forest cover change maps illustrate the extent and rate of reduction in Cambodia’s forest cover
change over the past 40 years. The maps focus on changes in evergreen forest, referred to as “dense
forest” in Cambodia. In English, Cambodia’s dense forest might also be termed primary or virgin forest.
Analysis of satellite images shows that in 1973 approximately 72.11 percent of Cambodia was covered by
forest. More recent images suggest that today’s forest cover is closer to 46.33 percent, inclusive of tree
plantation.
Both animated and static maps are included on this page. Seven videos animate the change in forest
cover for the entire country, while six static maps show more detailed views of particular areas. Regional
animations show the boundaries of Cambodia’s protected areas, comparing forest change inside
protected areas with that of unprotected areas. Most of Cambodia’s protected areas were designated in
the 1990’s. More information on protected areas, along with ODC’s static maps can be found on our
interactive page. The static maps can be used as a base layer for overlaying features and other kinds of
development information that is available on ODC.
Who made these maps?
ODC mappers began work on this project in June 2013. They are the first Cambodians to do this type of
work and were inexperienced in satellite image analysis at the beginning of the project. With training by
experts from Vietnam’s Can Tho University, they became increasingly skilled, and are now able to
analyze maps to a high standard. These maps represent a new technical tool, produced by Cambodians,
to help understand environmental changes and inform development planning.
Definitions
Cloud: Visible cloud cover at 30m resolution.
Dense forest: in Cambodia’s case, dense forest signifies evergreen forest, comprised of trees which do
not lose their leaves through seasonal abscission. Dense forest is mostly located at elevations higher
than 500m, although Cambodia has also had large areas of lowland evergreen forests in the past. Dense
forest can also be considered primary or virgin forest as it has never been cut.
Mixed forest: Primarily regarded as dry mixed deciduous forest (deciduous trees drop and regrow their
leaves seasonally.) Mixed forest may also include regrowth forest, stunted forest, mangroves, inundated
or “flooded” forest, and bamboo, as well as forest plantations growing rubber, acacia and eucalyptus or
other tree crops.
Non forest: Non forest is not dense forest, mixed forest, water or cloud. Non forest includes urban areas,
field crops, and fallow or barren land and other human-impacted areas.
Satellite: An object placed in earth’s orbit that is able to photograph the planet’s surface at great
distances. NASA’s Landsat satellites took the images used to generate the maps on this page.
Water: All bodies of water that are visible at 30m resolution.
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METHODOLOGY
ODC produced forest cover maps for 1973, 1989, 2000, 2004, 2009, and 2013 from satellite images. The
earliest images available for Cambodia date from the early 1970’s. ODC selected satellite images for
analysis based on their quality, including the absence of cloud cover.
Analysis of Cambodia’s pre-war forest, compared to forest cover in 1989, showed only minor changes,
while significant changes were observed between 2000 and 2013. Mappers were able to determine
where dense forest was lost – the changes are shown using contrasting colors. Dark green is used to
show dense forest. Red on a map denotes areas of lost dense forest that were first detected on that
year’s map. As the animation progresses to the next frame, red areas disappear to reveal the new status
of the land as either mixed forest or non forest.
Technical methodology
Each “forest cover map” is composed of 16 to 19 NASA satellite images, which were obtained from the
US Geological Survey (USGS). The images are free, publicly available and can be downloaded at the
USGS website.
Image classification was used to detect forest changes. This process involved converting multi-band
raster images into a single composite-band raster image. The composite-band raster image allowed the
mappers to identify five forest cover classifications to be mapped: dense forest, mixed forest, non forest,
water and cloud.
The 1973 forest cover map consists of 16 Landsat MSS images with 60m x 60m resolution. No Thematic
Mapper (TM) images were available for this year. A mosaic was created from these images, to which
color bands 3, 2 and 1 were applied to identify the Region of Interest (ROI). Landsat TM images were
used at 30m x 30m resolution to create the 1989, 2000, 2004, and 2009 forest cover maps, with color
bands 4, 3 and 2 applied. Landsat 8’s Operational Land Imager satellite images were used at 30m x 30m
resolution to create the 2013 forest cover map. The map was analyzed by applying color bands 5, 4 and 3
to identify the ROI.
A forest change detection model was used with the forest cover maps to depict the loss of forest from one
map to the next, shown on five additional maps known as “forest cover change maps”.
Each of the seven animations, one national and six regional, is composed of 11 static maps: the six forest
cover maps and the five forest cover change maps.
SCOPE & LIMITS
Although the Forest Cover Change maps are a product of rigorous analysis, a number of limitations and
potential mapping biases still persist.
1. Scope: The ODC forest cover maps show trends in forest cover change focusing on dense forest.
Classification is limited to dense forest, mixed forest, and non forest. Since the maps are based on
satellite images with a resolution of either 60 meters or 30 meters, it was not possible to differentiate the
specific tree species that comprise the forests. For this reason, the mixed forest classification may also
include tree plantations. At this resolution it was not possible to identify small pockets of deforestation.
2. Cloud cover: All of the satellite images used to produce the maps contained cloud cover. This
presents a challenge for image classification as information underneath the clouds cannot be detected.
To avoid this, ODC sought the clearest images with the least cloud cover. The 1973, 1989, 2000, 2004
and 2009 images contained between 1 to 10 percent clouds. The 2013 satellite images contained
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approximately 30 percent cloud coverage. In ODC’s forest cover maps, clouds are depicted as white
areas. Areas underneath clouds could not be analyzed.
3. Season: Cambodia has two seasons: rainy and dry. The landscape of the country changes during
each season. For example, vegetation is greener during the rainy season than during the dry season.
There are also variations in the size of water coverage between the seasons. Since image classification
involved combining multiple satellite images taken during different seasons, this may have led to slight
analytical errors.
4. Scan lines: A few satellite images contained scan lines. This created slight data gaps in image
analysis.
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