The other side of drought: Why shallow water-table forests may be resilient to climate change-linked-droughts


The other side of drought: Why shallow water-table forests may be resilient to climate change-linked-droughts

Tue, July 12, 10:30 - 12:30, Room 302


Flavia Costa, Scott C. Stark, Juliana Schietti

Variations in hydrological environments have been neglected in studies of tropical forest responses to climate change, despite ~50% of Amazonia having shallow water tables. We examine how water table depth filters plant composition and traits, affects forest dynamics and the resulting ecosystem behavior, with globally important consequences for drought responses.

Water availability to plants is one of the most important drivers of plant ecology, from species distribution to ecosystem functioning. This availability is defined by water input (via precipitation), water loss (via evapotranspiration), and, critically, water retention and storage (given by soil properties and topography). The large majority of studies of plant ecology focus on the first two drivers, which compose the climate, but tend to overlook the local water availability modulated by soil and topography (as might be captured, for example, in the water table depth, a key index of local water availability). Here we show how this hydrological component determines several patterns of plant distribution, acting as a filter of plant traits and thus affecting forest structure, composition, dynamics and ecosystem functioning. We show and discuss how this hydrological component is key to understanding forest responses to drought, from individual and population responses to canopy productivity. Last, we propose a theoretical framework on how to include this neglected factor in modeling of Amazon basin-scale forest responses to drought. This symposium is intended to be a synthesis of knowledge accumulated in the last 15 years of extensive and intensive work on gradients of water table depth in the Amazon. The perspective offered by this work suggests that water table depth can be an important filter of plant species and traits, which interacts with local hydrological properties to determine the impacts of droughts. Interestingly, the evidence suggests that in shallow water table depth forests, where there is frequently an excess of soil water that causes anoxic soil conditions, moderate drought conditions may enhance tree growth. This challenges the perspective of widespread and ubiquitous negative effects of climate change associated droughts on Amazonian forests, and may reconcile the contrasting reports of decreased productivity in deep water table biased forest plot networks and increased canopy function metrics observed with remote sensing, which capture shallow and deep water table forest regions. Furthermore, while some drought conditions may enhance growth in shallow water table depth forests, these forests also lack drought resilient functional traits, suggesting there is significant limitation to the resilience of these forests that has yet to be resolved. With the Amazon basin comprising up to 50% shallow water table depth forests, predictions of the impacts of climate change based largely on uplands with little access to soil water storage are likely inaccurate.

Introduction to the water table: why does it matter for plants and how it varies across geomorphology and soils
Flavia Costa*, Juliana Schietti, Marielle Smith and Scott Stark

The filtering effect of water table depth on plant functional traits
Juliana Schietti*, Maquelle Garcia, Edher Cordoba, Elisangela Rocha, Erick Jonathan Esteban, Leonardo Ziccardi and Flavia Costa

The spatial patterns of Amazonian Forest composition and structure as determined by water table depth
Thaise Emilio*, Juliana Schietti, Thaiane de Sousa, MANUEL ZEVALLOS, Priscila Costa, Gabriel Moulatlet and Flavia Costa

A remote sensing perspective on the effects of water table depth on forest structure and functioning
Marielle Smith*, Scott Stark, Juliana Schietti, Flavia Costa, Diogo Rosa, Dalton Freitas do Valle and Bruce Walker Nelson

Forest dynamics and responses to drought modulated by the water table depth
Erick Jonathan Esteban*, Thaiane de Sousa, Juliana Schietti, Carolina Méndez and Flavia Costa

A synthesis and theoretical perspective linking hydrological regimes with functional responses to understand the potential resilience of waterlogged Amazon forests
Scott Stark*, Flavia Costa, Juliana Schietti and Marielle Smith