Recovery from drought-induced dieback may lead to modified salt marsh vegetation composition

Abstract

Salt marshes are vital but vulnerable ecosystems. However, our understanding of disturbance-induced dieback and recovery processes in multi-specific marshes remains limited. This study utilized remote sensing data (2001–2021) to analyze a dieback event and subsequent recovery in the multi-specific San Felice marsh within the Venice lagoon, Italy. A significant dieback of Spartina maritima (Spartina) was identified in 2003, likely triggered by a drought event and heat stress. This resulted in a conversion of 4.6 ha of marsh predominantly colonized by Spartina (fractional cover of Spartina > 50%) in 2001 to bare soil in 2003. These bare areas were then gradually encroached by vegetation, indicating the occurrence of the recovery. Despite gradually gaining ground, Spartina only dominated 6.4 ha marshes in 2021, significantly lower than its pre-dieback area (21.3 ha). However, other species also encroached on the dieback area, such that the aboveground biomass returned to pre-dieback levels, indicating that the shift in marsh species composition that occurred as a consequence of the event compensated for this ecosystem service. Vegetation recovery, spanning from 1 yr to more than 18 yr, was found to be slowest in areas of lowest elevation. This study provides evidence that dieback and recovery can modify the species composition of multi-specific marshes over decades. These insights contribute to a better understanding of marsh resilience to drought and elevated temperature, both of which are likely to increase in the future.