Effects of Invasive Smooth Cordgrass Degradation on Avian Species Diversity in the Dafeng Milu National Nature Reserve, a Ramsar Wetland on the Eastern Coast of China

Invasive smooth cordgrass (Spartina alterniflora) has been expanding rapidly through the coastal wetlands of eastern China and these changes negatively affect local birds. In the Dafeng Milu National Nature Reserve (henceforth referred to as DMNNR), rapid degradation of spartina occurs after an increase in milu (Elaphures davidianus; hereafter elk) numbers and ecological hydrological engineering. We evaluated the impact of such degradation on the abundance and species diversity of birds in the DMNNR during 2017–2021. We found that the area covered by S. alterniflora decreased significantly in the study area at a rate of 310 ha per year and by 62% during 2017–2021 (p < 0.01). With this decrease in the S. alterniflora area, the species richness and abundance of birds first increased and then decreased. Songbird density clearly decreased but species richness did not significantly do so. This research demonstrated that during the initial stages of vegetation degradation, there was a positive effect on bird diversity. With the increasing vegetation degradation increases, both songbirds and waterbirds experience negative impacts. The DMNNR is an important stopover site for waterbirds in the East Asian–Australasian Flyway, and additional measures are needed to control vegetation degradation and to restore the native habitats for birds.