Annual Maps of Forests in Australia from Analyses of Microwave and Optical Images with FAO Forest Definition

Yuanwei Qin,Ralph Dubayah,Xiangming Xiao,Sean Crowell,Xiaojun Li,Josep G Canadell,Kevin Neal,Xiaocui Wu,Bo Zheng,Lei Fan,Berrien Moore,Russell Doughty,Martin Brandt,Qing Chang,Jorge A Celis,Hao Tang,Jean-Pierre Wigneron,Philippe Ciais

doi:10.34133/2021/9784657

Abstract

The Australian governmental agencies reported a total of 149 million ha forest in the Food and Agriculture Organization of the United Nations (FAO) in 2010, ranking sixth in the world, which is based on a forest definition with tree height > 2 meters . Here, we report a new forest cover data product that used the FAO forest definition ( tree cover > 10 % and tree height > 5 meters at observation time or mature) and was derived from microwave (Phased Array type L-band Synthetic Aperture Radar, PALSAR) and optical (Moderate Resolution Imaging Spectroradiometer, MODIS) images and validated with very high spatial resolution images, Light Detection and Ranging (LiDAR) data from the Ice, Cloud, and land Elevation Satellite (ICESat), and in situ field survey sites. The new PALSAR/MODIS forest map estimates 32 million ha of forest in 2010 over Australia. PALSAR/MODIS forest map has an overall accuracy of ~95% based on the reference data derived from visual interpretation of very high spatial resolution images for forest and nonforest cover types. Compared with the canopy height and canopy coverage data derived from ICESat LiDAR strips, PALSAR/MODIS forest map has 73% of forest pixels meeting the FAO forest definition, much higher than the other four widely used forest maps (ranging from 36% to 52%). PALSAR/MODIS forest map also has a reasonable spatial consistency with the forest map from the National Vegetation Information System. This new annual map of forests in Australia could support cross-country comparison when using data from the FAO Forest Resource Assessment Reports.

Highlights

The area, spatial distribution, and temporal dynamics of forests in Australia significantly influence biodiversity, carbon and water cycles, and climate [1,2,3,4,5]
The Phased Array L-band Synthetic Aperture Radar (PALSAR)/Moderate Resolution Imaging Spectroradiometer (MODIS) forest map reveals the extent and spatial distribution of forests, and most of them were distributed in eastern Australia (Figure 8(a))
When we used the Global Land Cover Validation Reference Dataset (2 m spatial resolution) from the United States Geological Survey (USGS) with a forest definition of tree height greater than 5 m to validate the PALSAR/MODIS forest maps, we reported an overall accuracy of ~90% in those PALSAR/MODIS forest maps [12, 13]

Summary

Introduction

The area, spatial distribution, and temporal dynamics of forests in Australia significantly influence biodiversity, carbon and water cycles, and climate [1,2,3,4,5]. Many efforts have been carried out to understand the spatial distribution and temporal changes of Australian forests. Australia’s State of the Forests Report (SOFR), a five-year national report on the status of forests, has been generated since 1998 by the Australian Bureau of Agriculture and Resource Economics and Sciences (ABARES), Department of Agriculture, Water and the Environment [6]. The differences in forest area and spatial distribution among the SOFR reports cannot be considered as the actual forest change over years because different approaches have been used to generate the forest maps [6]. Geoscience Laser Altimetry System (GLAS) observations onboard the Ice, Cloud, and land Elevation Satellite (ICESat) and the Phased Array L-band Synthetic Aperture Radar (PALSAR) data onboard the Advanced Land Observation Satellite (ALOS) were used to segment landscape and were combined with NVIS to generate a structure-based classification of Australian vegetation [9]

Methods

Results

Conclusion