Global analysis of the slope of forest land

Forests of the world constitute 1/3 of the total land area and are critical for e.g. carbon balance, biodiversity, water supply, and as source for bio-based products. Although the terrain within forest land has a great impact on accessibility, there is a lack of knowledge about the distribution of its variation in slope. The aim was to address that knowledge gap and create a globally consistent dataset of the distribution and area of forest land within different slope classes. A Geographic Information System (GIS) analysis was performed using the open source QGIS, GDAL, and R software. The core of the analysis was a digital elevation model and a forest cover mask, both with a final resolution of 90 metres. The total forest area according to the forest mask was 4.15 billion hectares whereof 82% was on slope less than 15°. The remaining 18% was distributed over the following slope classes, with 6% on a 15-20° slope, 8% on a 20-30° slope, and 4% on a slope >30°. Out of the major forestry countries, China had the largest proportion of forest steeper than 15° followed by Chile and India. A sensitivity analysis with 20 metres resolution resulted in increased steep areas by 1 percent point in flat Sweden and by 11 percent points in steep Austria. In addition to country-specific and aggregated results of slope distribution and forest area, a global raster dataset is also made freely available, to cover user-specific areas that are not necessarily demarcated by country borders. Apart from predicting the regional possibilities for different harvesting equipment, which was the original idea behind this study, the results can be used to relate geographical forest variables to slope. The results could also be used in strategic forest fire fighting and large scale planning of forest conservation and management.