Mapping alien and native forest dynamics in Chile using Earth observation time series analysis

Abstract

Chile is a global biodiversity hotspot and hosts a large proportion of the southern hemisphere’s temperate forests. The Chilean Valdivian temperate forest is a vulnerable ecosystem containing a highly ecologically valuable species assemblage. Productive forest plantations have involved deforestation of, and alien species introduction into, this ecosystem. This process has already severely impacted the western part of Chile (the Coastal Range) and is now occurring in the eastern part (the Andes), with forestry plantations promoted by government subsidies between 1974 and 2012. Archive Landsat satellite imagery classification and Google Earth Engine are used to assess land cover change over a 31-year period with a focus on alien species (Pinaceae and Eucalyptus spp.) spread and native (Nothofagus spp. and Araucaria araucana) deforestation. Results show a clear land cover pattern based on elevation: a higher altitude, relatively undisturbed area dominated by native forest (the Andes), and a lower altitude area where most human activity and related land covers are located (the valley area). The valley is highly dynamic because of constant land cover change due to forestry. Overall, Araucaria araucana cover has decreased over the study period, while Nothofagus spp. has remained relatively stable. Alien Pinaceae has decreased, while Eucalyptus spp. has remained stable. However, the results indicate that change analysis over long periods conceal dynamism. For example, Eucalyptus spp. sharply decreased between the 1980s and the 1990s and surged afterwards. Also, even though Nothofagus spp. cover dominates throughout the study period, change analysis shows a high degree of change in the valley area, indicating newly established Nothofagus spp. patches. Over the study period, long rotation Pinaceae plantations for timber have given way to shorter rotation forestry (alien Eucalyptus spp., native Nothofagus spp.) for pulp and local uses resulting from discontinuation of forest subsidies. In the absence of subsidies, only large-scale plantations can engage in long rotation forestry, as smallholders need the more stable income provided by shorter rotation forestry. Although higher elevations (the Andes) are dominated by native forest, several abandoned alien forest plantations may be the source of biological invasion. In addition, native forest degradation as a result of Araucaria araucana loss and shrub encroachment is occurring. Earth observation methods are key for forest and alien species monitoring and landscape management. They can enhance traditional, ground-based forest surveys and provide continuous and even retrospective monitoring of forest change thanks to the wide availability of current and historical satellite data.