Human-mediated dispersal redefines mangrove biogeography in the Anthropocene

Introduction of species by humans breaks down biogeographic boundaries and
results in the homogenization of species composition, yet empirical tests
of this impact in marine forest ecosystems are still scarce. Large-scale
planting aimed at reversing losses of mangroves has been the dominant
strategy for mangrove restoration adopted by many organizations in the
past decades, but there is a lack of quantitative understanding of the
impacts of such large-scale plantings on mangrove biogeography. Here we
used data collected before and after large-scale planting to compare the
species richness and compositional similarities among 72 mangrove sites
over a biogeographic scale (18-28 °N) in China. After the large-scale
planting, 15 of the mangrove species spread towards the higher latitudes,
reflecting the geographical barriers of the mangrove plants have been
broken. Local species richness of mangrove increased by 44.82% and
biogeographic compositional similarity of mangroves increased by 13.33%,
reflecting large-scale introduction and planting increase local diversity
of mangrove but enhance biological homogenization. The dispersal
limitation of mangrove communities reduced by 11.1%, which indicates that
the community assemblage process of mangrove changed obviously.
Worryingly, two alien species, Sonneratia apetala and
Laguncularia racemose, have dispersal across the biogeographic
scale studied, reflecting an increase in the risk of biogeographic
invasion. It is expected that biological homogeneity and species invasion
will further influence the functional biogeography of mangroves. Our
results highlight that mangrove biogeography is defined by human
activities in the Anthropocene.