Asymmetric response of Amazon forest water and energy fluxes to wet and dry hydrological extremes reveals onset of a local drought-induced tipping point.

Autor: Restrepo-Coupe N; Department of Ecology and Evolutionary Biology, The University of Arizona, Tucson, Arizona, USA.; School of Life Sciences, University of Technology Sydney, Sydney, New South Wales, Australia., O'Donnell Christoffersen B; Department of Biology, University of Texas Rio Grande Valley, Edinburg, Texas, USA.; Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA., Longo M; Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA., Alves LF; Institute of the Environment and Sustainability, University of California Los Angeles, Los Angeles, California, USA., Campos KS; Department of Environmental Physics, University of Western Pará-UFOPA, Santarém, Brazil., da Araujo AC; Brazilian Agricultural Research Corporation (Embrapa) Amazônia Oriental, Belém, Brazil.; Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Brazil., de Oliveira RC Jr; Brazilian Agricultural Research Corporation (Embrapa) Amazônia Oriental, Belém, Brazil., Prohaska N; Department of Ecology and Evolutionary Biology, The University of Arizona, Tucson, Arizona, USA.; School of Life Sciences, University of Technology Sydney, Sydney, New South Wales, Australia., da Silva R; Department of Environmental Physics, University of Western Pará-UFOPA, Santarém, Brazil., Tapajos R; Department of Environmental Physics, University of Western Pará-UFOPA, Santarém, Brazil., Wiedemann KT; Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA., Wofsy SC; Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA., Saleska SR; Department of Ecology and Evolutionary Biology, The University of Arizona, Tucson, Arizona, USA.
Jazyk: angličtina
Zdroj: Global change biology [Glob Chang Biol] 2023 Nov; Vol. 29 (21), pp. 6077-6092. Date of Electronic Publication: 2023 Sep 12.
DOI: 10.1111/gcb.16933
Abstrakt: Understanding the effects of intensification of Amazon basin hydrological cycling-manifest as increasingly frequent floods and droughts-on water and energy cycles of tropical forests is essential to meeting the challenge of predicting ecosystem responses to climate change, including forest "tipping points". Here, we investigated the impacts of hydrological extremes on forest function using 12+ years of observations (between 2001-2020) of water and energy fluxes from eddy covariance, along with associated ecological dynamics from biometry, at the Tapajós National Forest. Measurements encompass the strong 2015-2016 El Niño drought and La Niña 2008-2009 wet events. We found that the forest responded strongly to El Niño-Southern Oscillation (ENSO): Drought reduced water availability for evapotranspiration (ET) leading to large increases in sensible heat fluxes (H). Partitioning ET by an approach that assumes transpiration (T) is proportional to photosynthesis, we found that water stress-induced reductions in canopy conductance (G s ) drove T declines partly compensated by higher evaporation (E). By contrast, the abnormally wet La Niña period gave higher T and lower E, with little change in seasonal ET. Both El Niño-Southern Oscillation (ENSO) events resulted in changes in forest structure, manifested as lower wet-season leaf area index. However, only during El Niño 2015-2016, we observed a breakdown in the strong meteorological control of transpiration fluxes (via energy availability and atmospheric demand) because of slowing vegetation functions (via shutdown of G s and significant leaf shedding). Drought-reduced T and G s , higher H and E, amplified by feedbacks with higher temperatures and vapor pressure deficits, signaled that forest function had crossed a threshold, from which it recovered slowly, with delay, post-drought. Identifying such tipping point onsets (beyond which future irreversible processes may occur) at local scale is crucial for predicting basin-scale threshold-crossing changes in forest energy and water cycling, leading to slow-down in forest function, potentially resulting in Amazon forests shifting into alternate degraded states.
(© 2023 John Wiley & Sons Ltd.)
Databáze: MEDLINE
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