Land cover map of Yukon-Charley Rivers National Preserve, 2022

Swanson, David

doi:10.36967/2300010

A land cover map of Yukon-Charley Rivers National Preserve has been produced to replace an outdated map from 1991. The new map is intended for use at a scale of 1:24,000. It is based on Sentinel-2 satellite image data (10-m resolution), plus topographic and vegetation height data from the Alaska Statewide IFSAR digital elevation model (DEM; 5 m resolution, resampled to 10 m). The image data were smoothed using an edge-preserving filter. Training data points were located by examining the Sentinel-2 and higher-resolution image data, and topographic maps while referencing field plot data from multiple different projects: primarily the USDA-NRCS soil survey sample plots and the NPS Central Alaska Inventory and Monitoring Network vegetation monitoring plots. The training points were used to extract training data from the smoothed images, which was then used to classify the smoothed data from the whole study area. Classification was by a modification of the k-nearest neighbor method, and also by Random Forest for comparison. The two methods produced similar results; and the modified knn method appeared to be slightly better and was chosen for the final product. This map was made with minimal cost, thanks to extensive pre-existing vegetation data and free imagery. However, as a result of the reduced expenditure and effort, the map lacks customized vegetation type descriptions and a comprehensive error analysis. Thirty-eight land cover types were mapped, including 31 vegetated types, water, and 6 unvegetated or sparsely vegetated types. Bootstrap analysis using the training data, and overlap analysis of the maps by the two method, suggest that both had accuracies of greater than 80%, and possibly as high as 90% for the modified knn map. Comparison with the 1991 map suggests loss of coniferous forest due to fires, especially in the terrace and foothill landforms, and its replacement with shrubs, deciduous forest, and mixed forest. Upland white spruce forest appears to have been reduced in these areas, while lowland black spruce forest and woodland persisted in spite of the fires. Extensive areas of unburned subalpine spruce woodland are still present at higher elevations, where fires are rare. The total vegetated area on the Yukon River floodplain appears to have remained fairly stable since 1991, while the area of coniferous forest on floodplains appears to have decreased.

Land cover map of Yukon-Charley Rivers National Preserve, 2022

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