Niches of plant populations in mangrove reserve of Qi’ao Island, Pearl River Estuary

Thirty-two 10 × 10 m² quadrats were set up in four mangrove communities for the study of the niches of nine plants with horizontal and vertical resource sequences in Dawei Bay, Qi’ao Island, Zhuhai City. Generally, species diversities of natural mangroves were higher than those of plantations. The diversities decreased along sequence of substrate layer, shrub layer and tree layer in natural mangroves; and were highest on the shrub layer in plantations. At the horizontal resource sequence, the niche breadth varied 0.132–0.896 (B_(sw)) and 0.120–0.693 (B_(L)). The niche breadth of Acanthus ilicifolius and Aegiceras corniculatum were the highest and that of Spartina alterniflora was the lowest. At the vertical resource sequence, the niche breadth varied 0–0.400 (B_(sw)) and 0.333–0.747 (B_(L)). All the niche breadth values were the lowest except those of A. ilicifolius and A. corniculatum. The niche similarity of the populations varied 0–0.746 and 0–1.000 at the horizontal and vertical resource sequences, respectively. A. ilicifolius and A. corniculatum had niche overlap with all plants at the horizontal resource sequence, while the introduced Sonneratia caseolaris and Sonneratiaapetala had no such overlapping between six and five plants in the community, respectively. At the vertical resource sequence, A. ilicifolius and A. corniculatum had niche overlapping with all the populations. The more niche overlapping existed among the other populations. The results indicated that, currently, the mangrove plantation in Qi’ao Island had a simplex structure and composition of species. The status of plant populations’ niche was determined by the species selected and structure of afforestation. It is suggested to create forest gaps artificially and introduce Kandelia obovata saplings to reverse its current status of lower niche breadth, facilitate natural regeneration and spreading of A. corniculatum and A. ilicifolius, and accelerate the restoration process of natural mangrove. Simultaneously, the species matching and planting methods of mix stands should be emphasized in the future.