Impact of Fire on Savanna Vegetation Trends in Madagascar Assessed Using a Remote-Sensing Based Statistical Analysis

摘要

Fire is a factor in the disturbance of savanna vegetation dynamics. This factor interacts in a complex way with other factors such as land use and climatic conditions. Fire could be considered as a factor that maintains savanna or as an agent of its degradation. In a context of land degradation prevention, the goal of this study is to clarify the role of fires in trends of savanna vegetation cover. The study site is located in the Marovoay watershed, on the north-west coast of Madagascar. This is one of the five pilot sites of a national programme of soil erosion control called PLAE. The role of fires in trends of savanna vegetation cover was addressed though a landscape-scale analysis of the spatial relation between a fire regime indicator, which combines fire seasonality and frequency, and an indicator of vegetation cover change. These data were derived from MODIS remote sensing time series data covering the 2000-2008 period. For each type of savanna vegetation cover trends observed (negative, positive or stable), different multivariate regression models were fitted. The results of this study clearly support the idea that fires have widely varying impacts on savanna vegetation cover. Fires are a savanna management tool. But, their usages through the seasonality and the frequency should be adapted according to land use (agricultural area. pastoralism, protected area). To define a fire management plan on the landscape-scale, it will be necessary to study locally the interactions between fire usage, land use and vegetation cover trends. The methods based on remote sensing time series analysis provide relevant results. There are statistically significant relations, according to land use, in the Malagasy savanna between fire regime and vegetation cover trends.