2.2 Field investigations
Field investigations were conducted from December 2017 to July 2018. Based on a previous experimental design and the experience of local forestry workers, the selection criteria for each plot were as follows: (1) the plots must contain varying numbers of adult D. pectinatumindividuals, and D. pectinatum must be a canopy plant species; (2) the conditions within the stand must be relatively uniform and show limited human interference. if the location of the plot met the above criteria, a plot was randomly established within the stand. A total of sixty-eight 900 m2 (30 m×30 m) permanent plots inD. pectinatum communities were investigated according to the minimum area sampling method in the western (Bawangling, 30 plots), southwestern (Jianfengling, 30 plots) and eastern (Diaoluoshan, 8 plots) parts of Hainan Island. Note: Due to severe deforestation at the Diaoluoshan site, we established only 8 permanent plots at this location. All woody stems (including trees, shrubs, and lianas) with a diameter at breast height (DBH) ≥5 cm were identified to the species level, tagged, and mapped, and their DBH was measured. The nomenclature follows that used in the Flora of China (http://foc.eflora.cn/ ).
In each 30 m×30 m plot, three 25 m2 (5 m×5 m) subplots along the diagonal (upper left, middle, and bottom right) were also established to record the regeneration dynamics. In each 5 m×5 m regeneration plot, all free-standing woody plants < 5 cm in stem diameter were tagged and identified to the species level. Species were identified by local botanists, with nomenclature consistent with the Flora of China website (http://foc.eflora.cn/ ). Additionally, their health status, stem height and crown width were also measured. The regenerating individuals were considered those with emerged cotyledon leaves, indicating one-year-old plants (Gao et al. 2017). Data were ultimately collected for a total of 204 regeneration plots.