Abstract:

Aims Phytolacca americana is a serious invasive plant species, which has harmed biodiversity and arboreal regeneration in coastal protective forests in Shandong Province. Our objective was to reveal its mechanism of reproduction and dispersal in order to provide guidance for controlling its invasion.

Methods To study the spatial and temporal pattern of seed rain of P. americana, we conducted field surveys under Robinia pseudoacacia forest in Lingshan Bay National Forest Park from September to December 2008. We established five transects at 15 m intervals from forest edge to forest interior and within each transect set up 30 samples (1 m × 1 m) to survey seed densities. We also chose eight mother plants of P. americana at 10 m intervals in each transect and placed seed traps (30 cm × 30 cm × 10 cm) at 11 sample points at every 30 cm surrounding them. We collected fallen seeds one or two days. One-way ANOVA was used to test the diversity.

Important findings The quantities and densities of seed rain were 1 846-2 273 seeds and 621-1 382 seeds per square meter, respectively, and values decreased from forest edge to interior. In five transects, the average seed rain densities were 33.64%-60.80% of reproduction, and the total average seed rain density accounted for 49.52% of seed reproduction densities; the rest was removed by firewood collecting and seed predation by animals. Seed rain began in mid September and ended in late December, and it occurred on forest edges before forest interiors. There were two seed-rain peaks in late October and mid December, and maximum intensities were 32 and 59 seeds per square meter per day, respectively. The dispersal distance of seed rain decreased from forest edge to forest interior. The same pattern existed with increasing distance from mother plant. The maximal dispersal and weighted mean distances were 210-180 cm and 94.32-63.03 cm, respectively; the average weighted mean distance was 81.00 cm. Phytolacca americana seed rain had obvious spatio-temporal heterogeneity. Findings were important to predict the invasive potential of P. americana and the trend in community structure.

Key words: invasive species, Phytolacca americana, seed density, seed rain, spatial heterogeneity, temporal dynamics