Long-term phenological shifts in coastal saltmarsh vegetation reveal complex responses to climate change

The impacts of climate change on vegetation growth are attracting increasing global attention. While phenological changes have been extensively studied in terrestrial ecosystems, long-term temporal research on phenology-climate feedback in coastal saltmarsh ecosystems, particularly both at the community and species levels, remains limited. In this study, the spatial phenology of saltmarsh vegetation was studied in the Dutch Western Scheldt estuary over three decades (1993–2022), based on the Landsat satellite-derived 2-band enhanced vegetation index (EVI2), coupled to existing sequential maps of vegetation communities. Our results show that saltmarsh vegetation in specific zones greens up earlier, reaches peak greenness sooner, and undergoes a significantly extended growing season—patterns are broadly consistent with climate-driven shifts observed in other ecosystems. However, phenological responses varied across the tidal inundation gradient, with higher intertidal communities initiating growth earlier than lower zones, reflecting the added complexity introduced by future sea-level rise and altered hydrological regimes. Correlations with seasonal meteorological variables showed spatially variable effects: warmer springs advanced green-up, drier summers delayed peak growth and senescence, and higher winter precipitation extends the growing season. Moreover, phenological asynchrony among plant species underscores the influence of species-specific traits and adaptive strategies. Saltmarsh vegetation shows both broad phenological responses to changes in meteorological conditions and site-specific patterns influenced by tidal regimes. Species composition and environmental gradients drive these responses, highlighting the need to understand these interactions for targeting vulnerable species, guiding restoration, and maintaining key ecosystem services (such as carbon sequestration, flood risk reduction, and habitat provision) under climate change.