Efeitos das queimadas florestais sobre a biomassa herbácea no ecossistema de miombo em Niassa

Abstract

Uncontrolled forest fires represent a serious environmental problem, significantly impacting the structure and composition of forest ecosystems while contributing to the emission of greenhouse gases (GHGs) that drive climate change. However, the magnitude of these fires' impact on vegetation and GHG emissions remains poorly understood. This study aims to deepen the understanding of forest fires and their impact on GHG emissions, as well as on biomass and carbon storage in the miombo ecosystem in the districts of Marrupa, Majune, and Maúa, in Niassa province. To achieve this, a controlled burning experiment was conducted in each district. Blocks of 4 ha were established, within which 20 temporary plots measuring 50 m × 20 m were set up. The height of combustible material (grasses and herbaceous plants) was measured before and after the fire. GHG emissions were estimated indirectly using the IPCC equation, while herbaceous biomass was calculated based on a calibrated equation for the miombo ecosystem. Biomass comparisons between districts were performed using the Kruskal-Wallis test, followed by Dunn's test for multiple comparisons, and biomass analysis before and after burning was conducted using the Mann-Whitney test. To understand the spatial and temporal dynamics of fires, satellite data on burned areas (MCD64A1) and active fire hotspots (MCD14ML), obtained through the MODIS sensor, were used. Fire frequency, return interval, intensity, and density were determined for the period from 2014 to 2023. The results indicate that fires occur more frequently in Marrupa and Majune than in Maúa and that there is an inverse relationship between fire frequency and intensity. Furthermore, significant differences were observed in biomass values before and after the fires, with Majune presenting the highest biomass levels both before and after burning. Controlled fires significantly reduced herbaceous biomass in all districts. CO2 emissions were higher than those of CH4 and N2O, with values of 6.07, 7.52, and 3.99 tons in the districts of Marrupa, Majune, and Maúa, respectively. The findings of this study highlight the importance of controlled burning as a tool for understanding the impact of fire on herbaceous biomass and GHG emissions in the miombo ecosystem. Moreover, adopting fire management practices tailored to the fire regime patterns in each district promotes more effective fire and impact management.