Drought-driven wildfire impacts on structure and dynamics in a wet Central Amazonian forest

Abstract

While the climate and human-induced forest degradation is increasing in the Amazon, fire impacts on forest dynamics remain understudied in the wetter regions of the basin, which are susceptible to large wildfires only during extreme droughts. To address this gap, we installed burned and unburned plots immediately after a wildfire in the northern Purus-Madeira (Central Amazon) during the 2015 El-Niño. We measured all individuals with diameter of 10 cm or more at breast height and conducted recensuses to track the demographic drivers of biomass change over 3 years. We also assessed how stem-level growth and mortality were influenced by fire intensity (proxied by char height) and tree morphological traits (size and wood density). Overall, the burned forest lost 27.3% of stem density and 12.8% of biomass, concentrated in small and medium trees. Mortality drove these losses in the first 2 years and recruitment decreased in the third year. The fire increased growth in lower wood density and larger sized trees, while char height had transitory strong effects increasing tree mortality. Our findings suggest that fire impacts are weaker in the wetter Amazon. Here, trees of greater sizes and higher wood densities may confer a margin of fire resistance; however, this may not extend to higher intensity fires arising from climate change.

Analysis of how the spatial and temporal patterns of fire and their bioclimatic and anthropogenic drivers vary across the Amazon rainforest in El Niño and non-El Niño years

“…Our research establishes the vulnerability of grass-dominated ecosystems and disturbed strata to fire dynamics. These findings are corroborated by existing literature (Silva Junior et al, 2018;Da Silva et al, 2018;Xu et al, 2020;Pontes-Lopes et al, 2021) and fires escaping from pasture dominated areas to forested ecosystems is matter of significant conservation concern (Cano-Crespo et al, 2015).…”

Amazon fires in the 21st century: The year of 2020 in evidence

“…Fire is among the major types of disturbance responsible for forest degradation in the Amazon (Matricardi et al, 2020; Tyukavina et al, 2017), having negative impacts on rain‐forest structure and dynamics that can compromise forest carbon stocks and the capacity of forests to act as carbon sinks for more than a decade (Pontes‐Lopes et al, 2021; Rappaport et al, 2018; Silva et al, 2020). The health of people living in the Amazon can also be affected directly by large‐scale and frequent fires because they accentuate air pollution during the fire season, leading to hospitalizations from respiratory illnesses (Butt et al, 2021; Campanharo et al, 2021; Sant'Anna et al, 2020).…”

Forest Fire History in Amazonia Inferred From Intensive Soil Charcoal Sampling and Radiocarbon Dating

“…Humid Amazonian forests were long considered mostly fire-free systems (Sanford et al, 1985;Pontes-Lopes et al, 2021). Here we show, in one of the most intensively local sampled radiocarbon studies to date of fire in terra-firme forest soils, that fire was rare but recurrent in these systems, with maximum return times of hundreds rather than thousands of years.…”

“…Fires over the past several decades in Amazonia have been widespread and increasing in frequency due to a combination of deforestation, fragmentation, recurrent drought, and human ignition (Aragão et al, 2007). During the 2015/2016 El Niño event with record-breaking drought and temperature anomalies, wet forests in central Amazonia burned (Pontes-Lopes et al, 2021), highlighting how changing climate and land use are interacting to allow forests once considered fire-resistant to burn. Over the past decade, deforestation and burning have resulted in a loss of 71,000 km 2 of forest in Amazonia (INPE, 2020).…”