Examining spatial dynamics and interactions of planted alien, native, and invasive alien species in China’s largest artificial mangrove forest

The planted alien mangrove species (i.e., Sonneratia apetala, SOA) was deliberately introduced to control the growth and spread of invasive species (i.e., Spartina alterniflora, SA) and restore mangrove ecosystems in Qi’ao Island, the largest artificially planted mangrove reserve of China. However, the effects of the alien species triggered a debate over whether they invaded or restored the mangrove vegetation. There is a gap in observing the impact of planted alien species on invasive alien species and native species over long periods. This study employed high-resolution images with less than 1 m acquired in 2002, 2008, 2010, 2013, and 2016 to examine spatial dynamics and interactions between alien, invasive, and native species. Results showed that mangrove areas increased to 327.56 ha in 2016 from 79.63 ha in 2002, while the presence of the invasive species SA dwindled to 4.19 ha in 2016, down from 110.18 ha in 2002. The increase in mangrove stand areas was mainly due to the artificial planting of SOA. Most of the SA habitat was occupied by SOA from 2002 to 2016, suggesting that artificial SOA can effectively control the growth and extension of invasive SA. There was no notable transfer from native to alien species. This indicated that alien species did not significantly impact the selection of native species in our study area during the observed period. However, we found that the alien species demonstrates adaptability, limiting the expansion of native species. Therefore, we should not underestimate the invasive power of alien species in mangrove ecosystems. Its ecological and biological effects still need to be carefully assessed over an extended period. The findings provided insight into the impact of planted alien mangroves from the perspective of spatiotemporal changes in species compositions.