The estimated numbers indicate an astonishing immediate impact of the Pantanal’s 2020 wildfires in the vertebrate communities, even considering that the estimates do not reflect the complete figure of mortality, as hidden (e.g., underground), delayed or second order effects certainly caused an unknown number of deaths. In fact, late mortality may be caused not only by body burns but also due to changes in the vegetation and the consequent impacts on resource quality, availability, and productivity at every trophic level, ultimately leading survivors to starvation31,32,33,34,35. Mortality also may occur due to increased predation during displacement from affected home ranges31,36. The negative consequences may be stronger for small populations or species that require more time to recover36,37,38). Thus, the overall impact of the catastrophic wildfire that hit the Pantanal in 2020 on the vertebrate communities should be considered as substantially higher than our estimates of the direct mortality by the fire.
Our findings did not include several species killed by wildfires in the Pantanal, such as those animals figured in the news media and animals found out of our standardized survey protocol by the field personnel, collaborators, and firefighters. Among these species were large-bodied animals usually living at relatively low densities, such as the jaguar (Panthera onca), the puma (Puma concolor), the lowland tapir (Tapirus terrestris), as well as species such as the red-brocket deer (Mazama americana), the giant anteater (Myrmecophaga tridactyla), the marsh deer (Blastocerus dichotomus), the pampas deer (Ozotoceros bezoarticus), the collared peccary (Pecari tajacu). Other common carnivores not detected in our surveys were the crab-eating fox (Cerdocyon thous), the racoon (Procyon cancrivorus), the maned wolf (Chrysocyon brachyurus), the tayra (Eira barbara), ocelot (Leopardus pardalis), the coati (Nasua nasua), and the jaguarundi (Herpailurus yagouaroundi), among other species known to occur in the Pantanal39,40. Large-bodied vertebrates have been among the injured animals frequently found alive by rescuers after the fires in the Pantanal, indicating that they may be less prone to die immediately. Large animals may die days and weeks after the fire due to burnings, and this may explain the fact that species such as tapir, marsh deer, and jaguars were not detected in our surveys but were found dead elsewhere in the region. Medium to large animals were detected at larger distances from the transect line if compared with smaller animals, indicating that our decision on splitting the data set in these two groups was correct. Conceptually, the effective sample trip is defined by the distance from the transect line in which the number of animals detected beyond such distance equals the number of animals missed within this distance, and it is used to estimate densities41.
Indirect estimates for the Australian savannas suggest that nearly 15,780 vertebrates per km2 were affected by the 2019/2020 bushfires, due to direct mortality and displacement, starvation, habitat loss and impoverishment, among other indirect effects of fire28. Similar exercise conducted in the Pantanal for the 2020 wildfire resulted in approximately 1,710 affected vertebrates per km2 (at least 65 million native vertebrates) plus 4 billion invertebrates in 38,000 square kilometers30. In Bolivia, researchers adopted an expert-based approach to determine mortality rates due to fire and theoretical estimates of mammal population densities, suggesting that 295.7 mammals per km2 (5.9 million individuals) were killed by the 2019 wildfires that affected nearly 20,000 km2 of the Chiquitano Dry Forest29. Although these assessments may be considered valid attempts of estimating the impact of wildfires, they are not based on direct carcass counts, they do not account for the extremely variable landscape composition, vegetation biomass, and flammability among regions hit by these events. Comparisons among these numbers and the results we present in this article may be virtually impossible as methods also varied among these studies. It is important to highlight that our estimates for the Pantanal are certainly underestimates for some taxonomic groups. Among the expected undetected dead animals in the surveyed areas in the Pantanal we may include especially amphibians, snakes, rodents, and armadillos, among other animal groups composed of fossorial animals and wood hollow users. Many small-bodied species may have died in places where they can not be accounted for, or their bodies may have been completely calcined or covered by ash. However, as our estimates are based on direct accounting of carcasses, they may be considered a better approximation of the reality when compared with theoretically based estimates of densities and/or mortality due to wildfire.
Estimating the number of deaths among wildlife species due to fire is relevant to contribute to the discussion on the potential cumulative impact of recurrent wildfires on ecosystems, as extensive fires compose a plausible scenario under climate change worldwide1,2,3,4,42. Indeed, the climate change scenarios for the Pantanal region indicate a 30% rainfall decrease in relation to the average precipitation between 2070 and 2100, as well as an increase in temperature and frequency of the extreme climatic events20. However, there was already a 40% shortage in rainfall in the region in 202019, as well as an increase of 2°C in the average temperature since 198018, creating the ideal conditions that contributed to the 2020’s wildfires in the Pantanal wetland. In fact, there is a trend occurring in the Pantanal, as a 376% increase in annual average burned area has been registered for the last two decades, with 43% of the area not being previously burned during this period6. Drought variability in the Pantanal region is closely related to teleconnection patterns associated with sea surface temperature anomalies in the Atlantic and Pacific oceans43. Despite the extreme droughts in the Pantanal region seem to be linked to a temperature anomaly in the tropical Atlantic ocean19,43,44, there is a negative synergy between the extreme climatic event with locally inadequate human factors in causing uncontrolled fire15,45. The complicated perspective for the future of the Pantanal wetland also relies on the fact that moisture from the Amazonian rainforest plays a significant role in controlling summer rainfall in central-southern Brazil, including Pantanal46. Recent studies show that deforestation in the rainforest is connected to lower transfer of moisture for the Pantanal wetland47. Since deforestation and fire are increasing again in the Amazon rainforest15, a challenging scenario for the Pantanal also includes other contributing factors such as hydrological changes due to river damming48,49,50,51, soil erosion and deforestation in surrounding plateaus52,53, which can cause wetland area losses, exposing more areas to the risk of fire.
Pantanal is already the Brazilian ecoregion with the highest average fire foci per square kilometer54. Thus, the perspective of an increased frequency and extension of fire in the Pantanal and other tropical ecosystems poses a serious threat to the conservation of biodiversity and ecosystem services, as the cumulative effects may be considerable in a long-term perspective. In fact, the 2020 wildfires were not limited to the Pantanal wetland, as exceptionally large burning areas were also registered further south, from the vicinity of Buenos Aires in Argentina, crossing into the Chaco region of Argentina, Paraguay and Bolivia and heavily hitting the Chiquitano dry forests of Bolivia, as well as large portions of the Amazon rainforest and the Cerrado savanna in Brazil. Under this perspective, strategies capable of preventing wildfire disasters are key to avoid ecosystem degradation and economic losses, as well as increased emission of greenhouse gases, considering the climate change scenarios. One relevant instrument for such a strategy is the implementation of proper public policies. In Pantanal context, it is important to enact the Integrated Fire Management (IFM) National Bill n. 11276/2018, which is still under discussion in August 2021 in the Brazilian Chamber of Deputies, drafted with the participation of state agencies, scientists, and traditional and indigenous communities. Also, state-level legislation is relevant as it is more detailed and focused on regional socio-economic, ecological, and cultural context and nuances. In fact, Mato Grosso do Sul state approved a specific policy to regulate the use of fire55, and Mato Grosso—the other Brazilian state where the Pantanal wetlands are located—is currently developing its own policy. Both pieces of legislation should serve as the basis for the proper use of fire in the Pantanal, but awareness and training are highly necessary. The basis for these policies is fuel management, which has proven to be an effective way to prevent wildfires and even reduce the risks posed by the combination of biomass, weather, temperature, and drought56,57,58,59.
As wildfires pose a worldwide threat to ecosystem resilience and overall sustainability, it's worth reinforcing the need for (i) continuous monitoring for early detection of fire risk and fire events; (ii) the establishment of firefighter brigades in strategic locations with continuous operation; (iii) the improvement of logistic capabilities to allow effective access to distant and marshy areas in the floodplain, (iv) community education programs focused on proper fire use for biomass management purposes, (v) effective enforcement of fire policies; and (vi) implementation of wildlife rescue and rehabilitation centers. In the specific case of the Pantanal wetland, for instance, it would be necessary to effectively implement such strategies for fire management in connection with economy, biodiversity conservation, ecosystem management, and public policy, as it has been proposed by sustainability agendas48. The case of the Pantanal reminds us that integrated fire management, as well as the implementation of sustainable land use and restoration to mitigate the inevitable impact of climate change are a crucial part of our survival strategy, given our dependency on ecosystems, their biodiversity, and services.