Kazuo Takeda

Temporal dependence of burn severity assessment in Siberian larch (Larix sibirica) forest of northern Mongolia using remotely sensed data

Assessing burn severity is critical for understanding both the short- and long-term effects of fire disturbance on forest ecosystems. This study proposed a methodology to reconstruct burn severity from the Landsat imagery at different time lags after a fire (≤18 years) in Siberian larch (Larix sibirica) forest. The estimated accuracy of the burn severity models we developed indicated strong effects of forest recovery, image acquisition date and remote sensing predictors on the burn severity assessment. In the first several years after the fire, the dNBR (differenced Normalized Burn Ratio) was the most important remotely sensed index for assessing burn severity, followed by the dNDMI (differenced Normalized Difference Moisture Index) and dNDVI (differenced Normalized Difference Vegetation Index). However, the dNDMI was more important than the dNBR and dNDVI in explaining burn severity when larch forest regrowth dominated. The overall accuracy of the classification and regression tree models showed a decrease in accuracy from 83% to 62% depending on the lag times of burn severity assessment. The high severity class had the lowest omission and commission errors, followed by the low and moderate classes among lag times. Our evaluation of model transferability and thresholds of burn severity index demonstrates the advantage of the proposed methodology for rapid assessment of fire effects in boreal larch forest that will assist in understanding the complex relationships among forest fires and ecological processes in Eurasian boreal ecosystems.

Ground Improvement. Development of Effective Slope Protection Technique in Cold Regions by Use of Native Dwarf Bamboos as Ground Cover.

Following a comprehensive field investigation on the effectiveness of slope protection techniques in cold regions, it was found that conventional protective grids usually cease to function within a few years because they protrude from the ground surface by repeated freeze and thaw cycles, and that such frost damages are significantly reduced on slopes covered by native dwarf bamboos (Sasa nipponica). Further, it was confirmed that the modified protective grids having a cross section shaped like “reverse T” are more effective in preventing frost damages than the conventional grids shaped like “I”. Based on these findings, an improved slope protection technique is recommended in which native dwarf bamboos are used as a ground cover protected by a new type of grids.