Salinity‐induced limits to mangrove canopy height

Abstract

AimMangrove canopy height is a key metric to assess tidal forests' resilience in the face of climate change. In terrestrial forests, tree height is primarily determined by water availability, plant hydraulic design, and disturbance regime. However, the role of water stress remains elusive in tidal environments, where saturated soils are prevalent, and salinity can substantially affect the soil water potential.LocationGlobal.Time PeriodThe canopy height dataset provides a global snapshot of the maximum mangrove height geographical distribution for the year 2000. Climate and environmental variables extend over the period 1970–2018.Major Taxa StudiedMangroves.MethodsWe use global observations of maximum canopy height, species richness, air temperature, and seawater salinity—a proxy of soil water salt concentration—to explore the causal link between salinity and mangrove stature.ResultsOur findings suggest that salt stress limits mangrove height. High salinity favours more salt‐tolerant species, narrowing the spectrum of viable traits. Highly salt‐tolerant mangroves have evolved to cope with high salt concentrations in the soil, but this adaptation comes at a cost. They typically have lower rates of photosynthesis and growth, resulting in reduced productivity and smaller stature compared to more salt‐sensitive mangrove species. This suggests a causal link between salinity, biodiversity, and tree height, where high salinity selects for more salt‐tolerant species that tend to be less productive and shorter.ConclusionsWe hypothesize that the salinity‐induced limit to mangrove canopy height is the direct result of a reduction of primary productivity, an increment in the risk of xylem cavitation, and an indirect consequence of the decrease in biodiversity. As sea‐level rise enhances coastal salinisation, failure to account for these effects can lead to incorrect estimates of future carbon stocks in Tropical coastal ecosystems and endanger preservation efforts.

IUCN Red List of Ecosystems, Mangroves of the Red Sea and Gulf of Aden

“…Generally, increased heatwave seasons cause seawater heating and increase salinization, which inhibits mangrove growth. In contrast, in this province, mangroves are not likely to be impacted by salinization as they are well-adapted to harsh environments, including extreme salinity and temperature and limited nutrient (Perri et al, 2023).…”

“…Low leaf nutrient concentrations and low carbon-to-nutrient stoichiometric ratios are characteristics of mangrove stands in the Central Red Sea, which indicate severe nutrient depletion, particularly of Phosphorous (P) and Iron (Fe), across stands and suggest the likelihood of nutrient limitation of Central Red Sea mangroves (Almahasheer et al, 2016c). Nutrient limitation is attributed to lack of riverine nutrient input into the Red Sea, which has resulted in growth of dwarfed mangroves (Anton et al, 2020;Perri et al, 2023). Nutrient concentration is also suggested to be the main factor limiting the mangrove"s response to high temperature and low fresh water supply, as well as the biogenic character of the carbonates-dominated Red Sea sediments (Almahasheer et al, 2016b).…”

Responses of Physiological, Morphological and Anatomical Traits to Abiotic Stress in Woody Plants

“…Increased salinity leads to changes in forest structure, reducing tree height, basal area, leaf area index and creating less productive ecosystems dominated by dwarf species [208,209]. Under salt stress, woody plants regulate physiological traits in the short term and morphological as well as anatomical traits in the long term [210].…”