An Estimation of Forest Biomass Loss in Central Siberia Using PALSAR Data
Mihai Tanase(1,2), Thuy LeToan(2), Juan de la Riva(1) and Maurizio Santoro(3)
(1) University of Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain
(2) Centre d’Etudes Spatiales de la Biosphere, Edouard Belin 18 bpi 2801, 31401 Toulouse, France
(3) Gamma Remote Sensing AG, Worbstr. 225, CH-3073 Gümligen, Switzerland
Siberian boreal forests contain large amounts of biomass playing a significant role in the terrestrial carbon cycle. These forests are vulnerable to natural hazards (e.g. forest fires) and human impacts (e.g. use change, exploitation) especially while considering their slow recovery rate. The objective of this study was to quantify changes in forest cover in Central Siberia, using ALOS-PALSAR FBD data (polarizations HH and HV) acquired from June to August 2007 in the framework of Kyoto and Carbon Initiative. Changes were estimated using the forest/biomass map product of SIBERIA-I project. Two sites, covering around 50.000 km2 each were selected in regions with reduced unclassified areas of SIBERIA-I product. The classification algorithm was developed in the first site and applied without further modification to the second one. Classification’s accuracy assessment was conducted at the second site using as ground truth Russian forest inventory databases. The methodology comprised PALSAR data processing and classification in classes similar with those defined in SIBERIA-I project (water, smooth areas, forest classes <21m3/ha, 21-50 m3/ha, 51-80 m3/ha, >80 m3/ha). The intensities (FBD HH/HV) and their ration were used as classifiers the results being compared to the corresponding subsets of SIBERIA-I product. Changes of one class upwards or downwards were interpreted as possible classification errors and therefore were not taken into account.
Over the 10 year period, forests registered a net cover loss between 4 to 10 % of the area. Deforestation altered 10.7% to 12.6% of the area while forest regrowth was registered on only 2.3 - 3.4%. It has to be underlined that only abrupt changes in cover type were considered. Different causes could stand behind forest area loss (e.g. natural disasters, clear cuts etc.) but the geometric shape of cleared forests suggest and active deforestation process.