Short-term effects of drought on tropical forest do not fully predict impacts of repeated or long-term drought: gas exchange versus growth

Abstract

Are short-term responses by tropical rainforest to drought (e.g. during El Niño) sufficient to predict changes over the long-term, or from repeated drought? Using the world's only long-term (16-year) drought experiment in tropical forest we examine predictability from short-term measurements (1–2 years). Transpiration was maximized in droughted forest: it consumed all available throughfall throughout the 16 years of study. Leaf photosynthetic capacity was maintained, but only when averaged across tree size groups. Annual transpiration in droughted forest was less than in control, with initial reductions (at high biomass) imposed by foliar stomatal control. Tree mortality increased after year three, leading to an overall biomass loss of 40%; over the long-term, the main constraint on transpiration was thus imposed by the associated reduction in sapwood area. Altered tree mortality risk may prove predictable from soil and plant hydraulics, but additional monitoring is needed to test whether future biomass will stabilize or collapse. Allocation of assimilate differed over time: stem growth and reproductive output declined in the short-term, but following mortality-related changes in resource availability, both showed long-term resilience, with partial or full recovery. Understanding and simulation of these phenomena and related trade-offs in allocation will advance more effectively through greater use of optimization and probabilistic modelling approaches.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

Towards a global understanding of vegetation–climate dynamics at multiple time scales

“…Vegetation may respond to inter-annual climate variation on both intra-and inter-annual scales (Meir et al, 2018). Such inter-annual climate variation may occur e. g. in the form of precipitation variation or periodic atmospheric fluctuations like El Niño Southern Oscillation (ENSO, Poveda and Salazar, 2004;Kogan and Guo, 2017;Liu et al, 2017), the Pacific Decadal Oscillation (Chen et al, 2017), or Indian Ocean Dynamics (Hawinkel et al, 2015).…”

The Impact of a Simple Representation of Non-Structural Carbohydrates on the Simulated Response of Tropical Forests to Drought

“…This is reasonable in the control plot where it is plausible that the forest was in steady state (Metcalfe et al, 2010) and so fluxes from 2005 will be similar to those during the 2002-2004 period. In the TFE plot while there were some significant changes in observed carbon fluxes during the first 3 years of the experiment, (for example the production of leaves, flowers and fruits, and fine wood Meir et al, 2018)), the forest largely resisted the effects of the drought during this period (significant increases in mortality were not seen until 2005 (Rowland et al, 2015;Meir et al, 2018)) and so we can similarly expect Figure A1. The mean seasonal trend of simulated plant carbon expenditure (PCE) and forcing gross primary productivity (GPP) (Parazoo et al, 2014) for each gridbox in the fNSC =0.08 SUGAR simulations.…”

“…A full summary of experimental set up and the most recent collection of results from the site is available in Meir et al (2018).…”

Drought resistance increases from the individual to the ecosystem level in highly diverse neotropical rain forest: a meta-analysis of leaf, tree and ecosystem responses to drought

“…The results from the Tapajós and Caxiuanã experiments have been previously synthesised (e.g. Meir et al, 2009Meir et al, , 2018da Costa et al, 2010a) and much of our knowledge about leaf, tree and ecosystem scale responses to multi-year droughts in tropical forests originates from these experiments. Therefore, and because of the low number of replicates (i.e., 2) of such experiments, this meta-analysis will focus only on the effects of seasonal and episodic drought on leaf, tree and ecosystem functioning.…”

“…Uncertainties are partly the result of the biological diversity found in neotropical forests as the magnitude and direction of a response to drought is found to be strongly dependent on the species measured (Bonal et al, 2000a;Domingues et al, 2014). Also, uncertainties arise as droughts differ in length, periodicity and severity (Bonal et al, 2016;Marengo et al, 2011;Meir et al, 2018). Finally, ecophysiological responses to drought occur on a multitude of spatial and temporal scales.…”