Vulnerability of Amazon forests to storm-driven tree mortality

Abstract

Tree mortality is a key driver of forest community composition and carbon dynamics. Strong winds associated with severe convective storms are dominant natural drivers of tree mortality in the Amazon. Why forests vary with respect to their vulnerability to wind events and how the predicted increase in storm events might affect forest ecosystems within the Amazon are not well understood. We found that windthrows are common in the Amazon region extending from northwest (Peru, Colombia, Venezuela, and west Brazil) to central Brazil, with the highest occurrence of windthrows in the northwest Amazon. More frequent winds, produced by more frequent severe convective systems, in combination with well-known processes that limit the anchoring of trees in the soil, help to explain the higher vulnerability of the northwest Amazon forests to winds. Projected increases in the frequency and intensity of convective storms in the Amazon have the potential to increase wind-related tree mortality. A forest demographic model calibrated for the northwestern and the central Amazon showed that northwestern forests are more resilient to increased wind-related tree mortality than forests in the central Amazon. Our study emphasizes the importance of including wind-related tree mortality in model simulations for reliable predictions of the future of tropical forests and their effects on the Earth' system. A R 1995 Classification of multispectral images based on fractions of endmembers-application to land-cover change in the Brazilian amazon Remote Sens. Environ. 52 137-54 Aragao L E O C et al 2009 Above-and below-ground net primary productivity across ten Amazonian forests on contrasting soils Biogeosciences 6 2759-78 Baker T R et al 2004 Variation in wood density determines spatial patterns in Amazonian forest biomass Glob. Change Biol. 10 545-62 Boose E R, Serrano M I and Foster D R 2004 Landscape and regional impacts of hurricanes in Puerto Rico Ecol. Monogr. 74 335-52 Carlotto M J 1999 Reducing the effects of space-varying, wavelength-dependent scattering in multispectral imagery Int. J. Remote Sens. 20 3333-44 Chambers J Q, dos Santos J, Ribeiro R J and Higuchi N 2001 Tree damage, allometric relationships, and above-ground net primary production in central Amazon forest Forest Ecol.

Understanding the uncertainty in global forest carbon turnover

“…Table 3), tree mortality from ephemeral insect and pathogen outbreaks, which, at least in some regions, might be similar in magnitude to tree mortality from fire (Kautz et al, 2018) and liable to intensify with global warming (Seidl et al, 2017), is not explicitly simulated. Neither are stand-replacing windthrow events, which are the main natural disturbance in parts of temperate and tropical forests 485 (Negrón-Juárez et al, 2018;Seidl et al, 2014). Comprehensive assessments of past and potential future impacts on forests due to such disturbances requires a process-orientated modelling approach (Chen et al, 2018;Dietze and Matthes, 2014;Huang et al, 2019;Landry et al, 2016), which remains highly challenging.…”

Tree functional traits as predictors of microburst‐associated treefalls in tropical wet forests

“…Treefall patterns are highly variable across tropical landscapes (Marra et al, ; Negrón‐Juárez et al, ; Rifai et al, ), where a poorly understood source of this variability remains tree mortality mediated by microbursts. Depending on wind intensity and periodicity, tropical storms can result in landscape‐altering treefalls, particularly in old growth forests, as mid‐ to large‐stemmed, and tall trees are more prone to damage from high winds (Nagel & Diaci, ; Woods, ).…”

“…In addition to affecting vulnerability to wind damage, mechanical (i.e., root growth, tree size) and biophysical properties of forests (i.e., slope, soil properties) interact to influence damage type (Mitchell, ; Negrón‐Juárez et al, ). For example, compacted soil with low infiltration limits root growth depth and increases the risk of uprooting over snapping (Negrón‐Juárez et al, ). Alternatively, biophysical properties facilitating deeper root systems and stability may increase vulnerability of larger, less flexible trees to snapping (Mitchell, ).…”

The Guiana Shield rainforests—overlooked guardians of South American climate

“…Further afield in the west and southwest, wetting in Colombia during April−September may cause flooding, negatively affect economic activities (including coffee, fruit, cocoa and banana growing) and enhance the risks of landslides, whilst wetting and/or drying in the Amazon forest may lead to changes in the dryseason length, forcing shifts in tree composition and forest ecosystem stability noticeable in our lifetime (Sombroek 2001, ter Steege et al 2006, Feeley et al 2012. Changes in the rainfall pattern may also affect the structure and composition of the forests via edgeeffects (Cumming et al 2012) and increased frequency of storms and downbursts that are a major mechanism of tree mortality in mature forests (Nelson et al 1994, Chambers et al 2013, Marra et al 2014, Negron-Juarez et al 2018. In the distant south of the LPB, enhanced extreme weather events (droughts and floods) would likely impact agriculture and therefore the economy of several countries.…”