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.