Abstract
Global tree cover percentage is an important parameter used to understand the global environment. However, the available global percent tree cover products are few, and efforts to validate these maps have been limited. Therefore, producing a new broad-scale percent tree cover dataset is valuable. Our study was undertaken to map tree cover percentage, on a global scale, with better accuracy than previous studies. Using a modified supervised regression tree algorithm from Moderate Resolution Imaging Spectroradiometer (MODIS) data of 2008, the tree cover percentage was estimated at 500 m resolution in Eurasia. Training data were created by simulation using reference data interpreted from Google Earth. We collected approximately 716 high-resolution images from Google Earth. The regression tree model was modified to fit those images for improved accuracy. Our estimation result was validated using 307 points. The root mean square error (RMSE) between estimated and observed tree cover was 11.2%, and the weighted RMSE between them, in which five tree cover strata (0%–20%, 21%–40%, 41%–60%, 61%–80%, and 81%–100%) were weighted equally, was 14.2%. The result was compared to existing global percent-scale tree cover datasets. We found that existing datasets had some pixels with estimation error of more than 50% and each map had different characteristics. Our map could be an alternative dataset and other existing datasets could be modified using our resultant map.
Highlights
Forests, by playing an important role in regulating the climate and water resources, and by providing habitats for many species, are of great importance for life on Earth
We estimated the tree cover percentage in Eurasia at a pixel size of 500 m using the supervised regression tree method with modification using evaluation data collected in advance from the entire study area
Two new parts in the method of this study are: (1) training data of various kinds were produced through simulation from reference data based on images available in Google Earth; (2) tree-cover percentage was estimated for groups and the groups were further divided into subgroups so that the estimation agree with the randomly sampled evaluation data
Summary
By playing an important role in regulating the climate and water resources, and by providing habitats for many species, are of great importance for life on Earth. They have recently been converted to unsustainable forms of land use due to urbanization and deforestation by expanding human populations. About 13 million hectares of forest were lost annually worldwide in the last decade, though the rate of loss decreased compared with about 16.1 million hectares per year during the 1990s. The rate of deforestation was decreased in Asia, Africa, and America compared with the 1990s, especially in Brazil and Indonesia, while the loss of forest increased in Australia since 2000 [1,2]. Continuous field maps present some advantages to measuring the change in spatially complex land cover compared with traditional discrete classifications
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