Integrating UAV data for assessing the ecological response of Spartina alterniflora towards inundation and salinity gradients in coastal wetland

The overwhelming spread of Spartina alterniflora (smooth cordgrass) has put many native plant communities and coastal environments at risk. A better understanding of how S. alterniflora responds to inundation and salinity gradients will help manage the invasion of this species. However, current spatial quantitative analyses are insufficient. Thus, unmanned aerial vehicles (UAVs) and field sampling data were integrated to assess the ecological response of S. alterniflora to inundation and salinity gradients. This study aimed to determine the optimum ecological range of flooding and saline for S. alterniflora in Dafeng Milu National Nature Reserve in Jiangsu, China. Our results showed that the optimum ecological amplitude of S. alterniflora to flooding depth was [-0.07 m, 0.82 m] and the optimum mean growing point was 0.38 m. Furthermore, the optimum flooding time was [0 h,11.87 h], and the optimum mean growing point was 4.13 h. Our analyses also showed that soil salinity had significant effects on the growth of S. alterniflora. The optimum ecological amplitude of S. alterniflora to soil salinity was [13.77 g/kg, 22.57 g/kg], and the optimum mean growing point was 18.19 g/kg. This is the first spatially quantitative analysis to study the eco-hydrological mechanism driving both the aboveground biomass and height of S. alterniflora over the intertidal zone to the best of our knowledge. Determining the optimal ecological range for flooding and salt will provide a scientific basis for measures to establish the ecological control of S. alterniflora and to predict the expansion of S. alterniflora in response to rising sea levels.