ENSO Drives interannual variation of forest woody growth across the tropics

Abstract

Meteorological extreme events such as El Niño events are expected to affect tropical forest net primary production (NPP) and woody growth, but there has been no large-scale empirical validation of this expectation. We collected a large high–temporal resolution dataset (for 1–13 years depending upon location) of more than 172 000 stem growth measurements using dendrometer bands from across 14 regions spanning Amazonia, Africa and Borneo in order to test how much month-to-month variation in stand-level woody growth of adult tree stems (NPP stem ) can be explained by seasonal variation and interannual meteorological anomalies. A key finding is that woody growth responds differently to meteorological variation between tropical forests with a dry season (where monthly rainfall is less than 100 mm), and aseasonal wet forests lacking a consistent dry season. In seasonal tropical forests, a high degree of variation in woody growth can be predicted from seasonal variation in temperature, vapour pressure deficit, in addition to anomalies of soil water deficit and shortwave radiation. The variation of aseasonal wet forest woody growth is best predicted by the anomalies of vapour pressure deficit, water deficit and shortwave radiation. In total, we predict the total live woody production of the global tropical forest biome to be 2.16 Pg C yr −1 , with an interannual range 1.96–2.26 Pg C yr −1 between 1996–2016, and with the sharpest declines during the strong El Niño events of 1997/8 and 2015/6. There is high geographical variation in hotspots of El Niño–associated impacts, with weak impacts in Africa, and strongly negative impacts in parts of Southeast Asia and extensive regions across central and eastern Amazonia. Overall, there is high correlation ( r = −0.75) between the annual anomaly of tropical forest woody growth and the annual mean of the El Niño 3.4 index, driven mainly by strong correlations with anomalies of soil water deficit, vapour pressure deficit and shortwave radiation. This article is part of the discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

Drier tropical forests are susceptible to functional changes in response to a long‐term drought

“…) and El Niño impacts (e.g., Rifai et al . ) than other tropical forests, and may thus respond to environmental changes in unforeseen manner. These characteristics highlight the need of more research efforts focused in the African tropical forests.…”

“…However, these forests have received less research attention in regard to environmental change effects on their structure, composition and function than their Amazon and SE Asian counterparts (but see Lewis et al 2009Lewis et al , 2013. African tropical forests are in general different in diversity (Richards 1973;Parmentier et al 2007), soil (Moore et al 2018), baseline climate conditions (Malhi et al 2013) and El Niño impacts (e.g., Rifai et al 2018) than other tropical forests, and may thus respond to environmental changes in unforeseen manner. These characteristics highlight the need of more research efforts focused in the African tropical forests.…”

Wood allocation trade‐offs between fiber wall, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees

“…Furthermore, there are signs that extreme episodic droughts are intensifying because of stronger Atlantic north‐south sea surface temperature gradients (Cox et al, ; Erfanian, Wang, & Fomenko, ). Episodic droughts, most notably in 2005, 2010, and 2015 have resulted in reduced tree growth and increased mortality in neotropical forests, specifically in the ever wet forest of the Amazon Basin (Feldpausch et al, ; Phillips et al, ; Rifai et al, ). Furthermore, increased drought and heat have been identified as possible drivers of a long‐term trend of increasing tree mortality in the Amazon Basin resulting in a reduction of the Amazon forest carbon sink strength (Brienen et al, ; McDowell et al, ).…”

Chimpanzee feeding ecology and fallback food use in the montane forest of Nyungwe National Park, Rwanda

“…In tropical forests, seasonality in tree phenology (and thus food resource availability for primary consumers) is largely mediated by meteorological variation, pollinators and seed dispersers (Rifai et al, ; van Schaik, Terborgh, & Wright, ). Animals that rely on vegetative foods are often subjected to seasonal variation in food abundance (Grueter et al, ; Janson & Chapman, ; Terborgh, ).…”