Assessing the effect of controlled burning and grazing on vegetation change in the grasslands of Aso region using satellite image analyses

The grasslands of Aso region have long been maintained by controlled burning and cattle grazing. In the present study, the effects of controlled burning and grazing on the grassland maintenance was quantitatively investigated using satellite images. Data on practices of controlled burning and cattle grazing for 170 pasture lands around Mt. Aso were collected. Landsat images of the pasture lands in three periods (Period I: before burning, Period II: after burning, and Period III: after grazing) from 1999 to 2014 were used for the analysis, and in each image, mean NDVI (Normalized Difference Vegetation Index) was calculated for each pasture land. The effects of year, burning, grazing and burning-grazing interaction on the NDVI of each period and the NDVI differences between two periods were investigated. In all analyses, the effects of year and burning on NDVI were significant (p<0.01). The decreases of NDVI in the burned pasture lands were observed, indicating that burning may have the potential to impede the grassland succession to forest. As for grazing, there were significant effects of grazing on the NDVI in Period II and the NDVI difference between Periods II and III (p<0.05). In Period II, NDVI were greater in the pasture lands where grazing was conducted in the previous year, suggesting that feces and urine from grazing cattle might have promoted growth of vegetation. The significant NDVI decreases from Periods II to III in the grazed pasture lands might have been resulted from the decreases in the amount of plant biomass by cattle grazing. The interaction effect of burning and grazing was also significant in Period III (p<0.05), and the effect of burning was only significant in the grazed pasture lands. These results indicated that burning and grazing in combination with burning be useful for grassland maintenance in the region.