Effects of the land-use change on fire patterns in the Gran Chaco ecoregion

Abstract

The Gran Chaco landscape was made up of an aggregate of dry forests, savannas, and grasslands, maintained by periodic fires produced by native populations. However, it has observed various modifications in land use over the last centuries. First, the fire regimes decreased due to the introduction of domestic herbivores and a consequent reduction in fine fuels and brush encroachment. More recently, towards the second half of the last century, there was an increase in the frequency of fires associated with prescribed burns aimed at the control of woodland.

This research project studied the influence of land-use change in the fire patterns of the Gran Chaco Ecoregion by through (i) a temporal analysis of land cover change, (ii) a temporal analysis of burned area, and (iii) an analysis of the effect of cropping extent on area burned. The spatial analysis was performed with data products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). This spatial analysis was performed over a temporal series of 18 years, from the year 2001 to the year 2019. The pre-processing of the data was performed on Google Earth Engine and the statistical analysis was done through R studio version 4.0.0. The results show that the Gran Chaco is under constant change of land use that result in modifications of the landscape.

The main findings were that the increase of croplands and grasslands area increased for the first nine years and then decreased while the burned area showed a decrease tendency at the beginning of the study period. These changes in the landscape vary depending on the area of the Gran Chaco being observed, as well on the time frame considered. According to the analysis, the cropland and grassland areas increased during the first half of the study period, while the burned area decreased. On the last years of the study period, cropland and grassland decreased, while burned area presented more variability. The decrease of croplands and grasslands can be as consequence of land abandonment. As for the geographical distribution of changes, the area of the Gran Chaco that observed greater changes during the study period was the fraction located in Paraguay. The unexpected initial high rates of burned area can be related to the historical use of the fire to clear the land.