Abrupt increases in Amazonian tree mortality due to drought–fire interactions

Abstract

Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes. Based on results of a large-scale, longterm experiment with annual and triennial burn regimes (B1yr and B3yr, respectively) in the Amazon, we found abrupt increases in fire-induced tree mortality (226 and 462%) during a severe drought event, when fuel loads and air temperatures were substantially higher and relative humidity was lower than long-term averages. This threshold mortality response had a cascading effect, causing sharp declines in canopy cover (23 and 31%) and aboveground live biomass (12 and 30%) and favoring widespread invasion by flammable grasses across the forest edge area (80 and 63%), where fires were most intense (e.g., 220 and 820 kW·m −1 ). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with <1% in nondrought years. These results show that a few extreme drought events, coupled with forest fragmentation and anthropogenic ignition sources, are already causing widespread fire-induced tree mortality and forest degradation across southeastern Amazon forests. Future projections of vegetation responses to climate change across drier portions of the Amazon require more than simulation of global climate forcing alone and must also include interactions of extreme weather events, fire, and land-use change.forest dieback | fireline intensity | stable states | MODIS | fire mapping

Multi-year MODIS active fire type classification over the Brazilian Tropical Moist Forest Biome

“…observed in 2010 over regions in eastern Mato Grosso, south east, and central Pará, and this has been documented by Brando et al (2014).…”

“…The annual number of classified forest and maintenance fires have similar temporal pattern, with a correlation of 0.85. The greatest numbers of classified forest fires occurred in 2007 and 2010 and this was also noted by Morton et al (2013) for southern Amazonia and by Brando et al (2014) for eastern Mato Grosso, and was suggested as being related to the drier conditions in these years Brando et al 2014). The forest and deforestation fires have a less similar temporal pattern with a correlation of 0.59.…”

“…vegetation and soil cover) and condition, and the degree of char and mineral ash deposition. Forest and deforestation fire types occur in forests which, due to their vegetation cover and drainage, are likely to have different fluxes of latent and sensible heat compared to maintenance fires that occur on pasture and crop lands (Carlson, Gillies, and Perry 1994;Weng, Lu, and Schubring 2004;Bagley et al 2013;Brando et al 2014). The local surface temperature may be modified by any change in albedo caused by deposition of char and mineral ash (Jin and Roy 2005;Roy et al 2010).…”

Deforestation: Carving up the Amazon

“…Tree mortality from heat and fire damage that year was more than four times that of a normal year 8 , especially along the forest edge, which the researchers burn every three years in a cycle emulating traditional Amazonian agricultural practices, says ecologist Paulo Monteiro Brando of Brazil's Amazon Environmental Research Institute in Brasília. In the Amazon, burning is the cheapest and most effective way for farmers to clear fields and give them a nutrient boost before planting crops, or rid them of ticks that plague livestock.…”

Predictores antropogénicos y biofísicos de deforestación en la Amazonia: hacia la integración de actividades REDD+

“…Average dry season length (number of months with precipitation ≤100 mm) maps of Amazon basin (2B) adapted from Brando et al (2014). Estimated pattern of biomass and carbon accumulation in Amazonian forests: dense rainforest on nonflooding lowlands (A), dense rainforest on flooded lowland (B), semideciduous seasonal nonflooding forest (C), semideciduous seasonal flooding forest (D), seasonal forest savanna (E), and seasonal woodland savanna (F).…”