Conservation management of abandoned paddy fields in Asia: semi-natural marshes with low-intensity bovid grazing have higher biodiversity.
Semi-natural marshland is becoming increasingly prevalent in Asia as a result of the continuing abandonment of rice cultivation. Although these marshes are important habitats for aquatic animals, they are susceptible to terrestrialization. Large mammalian herbivores that can retard terrestrialization are in decline globally, but domesticated bovids may serve as their surrogates, and could be used for managing semi-natural marshes. Relevant research in Asia is lacking, however. Aquatic macroinvertebrates were sampled in both the wet and dry seasons from 26 freshwater marshes (abandoned paddy fields) across Hong Kong, encompassing 15 sites grazed by feral bovids (yellow cattle and water buffalo) and 11 ungrazed sites. The aim was to investigate seasonal variation in the effects of bovids on macroinvertebrate communities in monsoonal marshes. Four decades after paddy cultivation had been abandoned, semi-natural marshes with low-intensity bovid grazing (0.06-0.14 cattle ha-1) had significantly higher (16%) site-scale γ-diversity. Macroinvertebrate communities at grazed sites had more Coleoptera and larval Odonata, and differed markedly from those at ungrazed sites. The effects of grazing on diversity and composition were unaffected by season, but season itself was a significant predictor of α- and β-diversity and species composition. This study is the first to record the responses of aquatic macroinvertebrate diversity and composition to large-mammal grazing in Asian marshlands. Given that bovid grazing at low intensity can control plant growth, with concomitant benefits for wetland diversity, it is suggested that targeted grazing of short duration could be used for conservation management of abandoned paddy fields.