Saltwater Exposure Affects Leaf Structure in a Coastal Forest

The Science

Sea level rise and increasing storms are stressing coastal forests, but the degree to which saltwater exposure changes tree leaves’ structure and function is poorly understood. This study measured how leaf shape—or specific leaf area (SLA), which is the ratio of leaf area to mass—changed along the natural salinity gradient of a tidal creek. Researchers found that salinity significantly affected SLA changes after accounting for the effect on different species. Trees in the downstream areas of the creek had lower SLA with thicker, smaller leaves, which is consistent with increased stress.

The Impact

Greenhouse and laboratory studies have examined how trees respond to increasing exposure to saltwater, but how trees respond is unclear in the real world with rising sea levels and increasing storms. Study results are consistent with the idea that the stress of chronic salinity exposure changes tree leaf shape and function, likely weakening their physiology and setting in motion processes that lead to forest death. These findings are thus useful for understanding the growing effects of saltwater intrusion into upland forests, as well as parameterizing and testing ecosystem-scale models simulating climate change and storm disturbances in coastal forests.

Summary

This study took advantage of a temperate forest creek’s natural salinity gradient to study how species differences, canopy position, and salinity exposure were associated with changes in SLA. Trees directly exposed to the tidal creek had lower SLA in higher-salinity plots, which is consistent with greenhouse studies reporting that the stress of chronic salinity changes leaf morphology and tree physiology. The study concludes that incipient ecosystem state shifts at the coastal interface may be predictable by observing changes in leaf-level parameters like SLA, which is a change that typically precedes tree death and the formation of “ghost forests.” Further integrated research using models and larger-scale manipulative field experiments is crucial to fully understanding ongoing structural and functional changes in coastal forests worldwide.

Principal Investigator

Vanessa Bailey
Pacific Northwest National Laboratory
[email protected]

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

Fieldwork for this study was performed as part of the Predicting Ecosystem Resilience through Multiscale and Integrative Science (PREMIS) Initiative, a Laboratory Directed Research and Development program at Pacific Northwest National Laboratory (PNNL), and supported by the Smithsonian Environmental Research Center. Support was received from a U.S. Department of Energy (DOE) Science Undergraduate Laboratory Internship. Data analysis and writing were supported by Coastal Observations, Mechanisms, and Predictions Across Systems and Scales—Field, Measurements, and Experiments (COMPASS-FME), a multi-institutional project funded by DOE’s Biological and Environmental Research program as part of the Environmental System Science program. PNNL is operated by Battelle for DOE under Contract DE-AC05-76RL01830.

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