Abstract:

Aims Shorea wantianshuea is an endangered tree species of Dipterocarpaceae in Xishuangbanna seasonal rain forest, and is listed in the Plant Red Book under Grade Ⅰ in China. This species regenerates exclusively from seeds. Our objective was to determine the fate of seedlings (including their growth and survival) following a mast fruiting event. Results will be useful in restoring this species and degraded natural forests dominated by it.
Methods In early December 2004, after mast fruiting of S. wantianshuea, we established three parallel 20 m×100 m transects spaced 50 m apart within an area of 100 m×200 m spanning from valley bottom to ridge top. Each transect was stratified into five contiguous plots of 20 m and near the center of each plot two 3 m×3 m quadrats were established. We labeled all newly established S. wantianshuea seedlings in each quadrat, recorded seedling height, basal stem diameter and number of leaves every 2-3 months over a 10-month period and calculated death rate, herbivory rate and survival rate of the seedlings. At the end of the survey, we destructively sampled seedlings and determined leaf areas, total dry weight, root-shoot ratio and specific leaf area.
Important findings Many S. wantianshuea seedlings established after the mast-fruiting event did not recruit into its natural population because of high mortality rate and herbivory rate caused by seasonal drought stress, small mammals and other predators. The density of seedlings was as high as 2.76 plants·m^-2 in December 2004 (first census), but was less than 0.26 plants·m^-2 in September 2005 when the study ended. Seedling mortality rate was high during the dry season, particularly after the first two months. The final seedling mortality rate on ridge-top and lower-ridge sites, 55% and 54%, respectively, were higher than those on other sites, with a gradually increase from valley bottom to ridge top. Herbivory rate in the first census was low and in 8 of 15 sites no seedlings were gnawed or pulled. At the end of the study, mean seedling height was 17.9, 19.7, 18.4, 13.0 and 12.1 cm in valley-bottom, lower-slope, medium-slope, lower-ridge and ridge-top sites, respectively; however, no significant differences were observed in seedling height and other growth parameters.

Key words: Shorea wantianshuea, seedling, growth and survival, mast-fruiting event, Xishuangbanna seasonal rain forest