Item

Abstract

Tropical woody plants store∼230 petagrams of carbon (PgC) in their aboveground
living biomass. This review suggests that these stocks are currently
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Annu. Rev. Earth Planet. Sci. 2019.47:555-581. Downloaded from www.annualreviews.org
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growing in primary forests at rates that have decreased in recent decades.Droughts are an important
mechanism in reducing forest C uptake and stocks by decreasing photosynthesis, elevating
tree mortality, increasing autotrophic respiration, and promoting wildfires.Tropical forests were a
C source to the atmosphere during the 2015–2016 El Niño–related drought, with some estimates
suggesting that up to 2.3 PgC were released. With continued climate change, the intensity and
frequency of droughts and fires will likely increase. It is unclear at what point the impacts of severe,
repeated disturbances by drought and fires could exceed tropical forests’ capacity to recover. Although
specific threshold conditions beyond which ecosystem properties could lead to alternative
stable states are largely unknown, the growing body of scientific evidence points to such threshold
conditions becoming more likely as climate and land use change across the tropics.
Droughts have reduced forest carbon uptake and stocks by elevating tree mortality, increasing
autotrophic respiration, and promoting wildfires.
Threshold conditions beyond which tropical forests are pushed into alternative stable states are becoming more likely as effects of droughts intensify.