Widespread Amazon forest tree mortality from a single cross‐basin squall line event

Abstract

Climate change is expected to increase the intensity of extreme precipitation events in Amazonia that in turn might produce more forest blowdowns associated with convective storms. Yet quantitative tree mortality associated with convective storms has never been reported across Amazonia, representing an important additional source of carbon to the atmosphere. Here we demonstrate that a single squall line (aligned cluster of convective storm cells) propagating across Amazonia in January, 2005, caused widespread forest tree mortality and may have contributed to the elevated mortality observed that year. Forest plot data demonstrated that the same year represented the second highest mortality rate over a 15‐year annual monitoring interval. Over the Manaus region, disturbed forest patches generated by the squall followed a power‐law distribution (scaling exponent α = 1.48) and produced a mortality of 0.3–0.5 million trees, equivalent to 30% of the observed annual deforestation reported in 2005 over the same area. Basin‐wide, potential tree mortality from this one event was estimated at 542 ± 121 million trees, equivalent to 23% of the mean annual biomass accumulation estimated for these forests. Our results highlight the vulnerability of Amazon trees to wind‐driven mortality associated with convective storms. Storm intensity is expected to increase with a warming climate, which would result in additional tree mortality and carbon release to the atmosphere, with the potential to further warm the climate system.

The steady-state mosaic of disturbance and succession across an old-growth Central Amazon forest landscape

“…Observed Amazon tree mortality and recruitment rates have increased since the mid 1970s (4), and particularly high mortality rates occurred in 2005 from drought and strong wind storms (33,34), with the potential for additional mortality from the 2010 drought (35,36). These high mortality events may indicate a shift toward more dynamic disturbance regimes, yet it is unknown whether this is part of a long-term climate-related trend, or a transient phenomenon.…”

Windthrow Variability in Central Amazonia

“…Only windthrows located >2 km away from urban areas and larger than 5 ha were considered in our analysis. Examples of windthrows over our study area have been published in our previous studies (e.g., Figure 2 in [3] and Figure S5 in [8]). To identify windthrows, a spectral mixture analysis (SMA) [46,47] was applied to the Landsat images.…”

“…Endmembers for GV was green cecropia and for shade a lake in our Landsat scene as shown in Chapter 7 in Adams and Gillespie [48]. In windthrow areas, a large increase in bare wood from downed trees is exposed to the satellite sensor, yielding a high mid-infrared reflectance (band 5, 1550-1750 nm, in Landsat 5 and Landsat 7) that lasts for about a year [3,4]. The fractions of GV and NPV were then normalized without shade [48] as GV/(GV + NPV) and NPV/(GV + NPV).…”

“…They are produced by downbursts [1][2][3], which are strong descending winds associated with severe convective storms [1][2][3][4][5] that create gaps of uprooted or broken trees [6]. These gaps vary in size from a single tree to thousands of hectares of forest [4,[6][7][8].…”

Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia

“…Spatial variation in CWD stocks across the landscape may respond both to short-term climatic disturbances (e.g. Phillips et al 2009;Negrón-Juárez et al 2010) and to long-term differences in forest dynamics in response to environmental characteristics (Keller et al 2004;Malhi et al 2006;Chao et al 2009a). Soils represent an important environmental gradient in Amazonia, with a wide variety of soil types across the Basin and with diverse chemical and physical conditions (Quesada et al 2010;.…”