The role of fire in the vegetation dynamics of upland savannas of the Venezuelan Guayana

Abstract

The frequent occurrence of fires in Canaima National Park, Venezuelan Guayana, is of great concern in the region. Fire, mostly originating on savannas, is considered a threat because of its impacts upon ecosystems, triggering a process of forest substitution by treeless savannas. In addition, the fires affect the well-being of Pemon indigenous communities, the hydroelectrical industry, and activities carried out by institutions and other stakeholders in the CNP. Here we present the main results of a long-term study of fire behavior and fire effects on biodiversity and biomass production in savanna ecosystems of the CNP. We simulated Pemon traditional methods of fire management by burning a series of 31 savanna plots in different periods of the dry season over a seven-year period. We demonstrate that (a) fires can occur under a wide range of weat her conditions and fuel characteristics, which in turn lead to a high variability in fire intensities, temperatures and spread rates, flame lengths, burn efficiencies, and ash production; (b) wind speed and fine fuel load constitute the principal drivers of fire behavior; and, (c) opposite to what was long believed, fires never reach an annual frequency but occur every 2, 3, or 4 years, due to the low recovery rates of the vegetation. Because fire could lead to a variety of scenarios depending on the amount of biomass (176–1.271 g m−2), live/dead ratios (0.36–3.60) and biodiversity (species abundance and composition), we believe that patch mosaic burning can be used as a management tool for biodiversity conservation and to reduce the risk of hazardous wildfires by creating a patchwork mosaic with different fire histories to generate heterogeneity across space and time. This practice would not only help preserve different ecosystems but also the sustainable use of natural resources by the Pemon people in the park.