Mapping peatlands in boreal and tropical ecoregions

© 2018 Elsevier Inc. All rights reserved. Peatlands are a class of wetlands that are defined as having saturated soils, anaerobic conditions, and large deposits of partially decomposed organic plant material (peat). Occurring in ecozones from the tropics to the arctic, peatlands are estimated to cover just under 4.5 million km2, roughly 3-5% of the Earth’s land surface (Maltby and Proctor, 1996). Although they cover a small amount of land globally, peatlands are estimated to store ~ 30% of the Earth’s soil carbon (C) (Gorham, 1991, Botch et al., 1995, Lappalainen, 1996, Zoltai and Martikainen, 1996, Clymo et al., 1998, Moore et al., 1998, Yu et al., 2010, Page et al., 2011), making them crucial to the global C cycle. Therefore, it is vital to obtain improved estimates of peatland distribution across the globe, as well as to monitor disturbances due to climate change or human activity. Efforts to map global wetlands from MODIS or other coarse resolution optical sources are ineffective in detecting and mapping peatlands. With coarse (250 m-1 km resolution) data, peatlands typically are grouped with a more general wetland class. Since peatlands are often small and interspersed with upland and other wetland types, it is essential to use finer resolution data (~ 30 m or better) to distinguish peatland types as described further in this article. Advanced remote sensing methods that use a combination of data sources and imagery from multiple seasons are necessary to capture the hydrologic and phenological variation that characterizes the diversity of peatlands that exist on the landscape. This article reviews the need for peatland mapping in boreal and tropical systems and summarizes applications of remote sensing for this purpose. Before mapping any landscape, it is necessary to have an understanding of the systems to be mapped. Knowledge of the characteristics of the ecosystems allows for informed decision making when choosing the combination of remote sensing data sources to best distinguish and classify the region of interest. In this article, we begin with background information on peatlands, followed by a review of mapping approaches from the literature and lastly, provide three examples of using multisensor, multitemporal optical, and radar data for mapping peatlands. The multisensor and multidate approaches are shown through examples to be more effective than using a single date of imagery and/or a single sensor