The intensity of seasonal drought is one of the strongest predictors that affect the tree species distribution in tropical forest. Previous studies were focused on the effect of seasonal drought on seedling community under forest canopies and little was reported on the ecological processes of seedlings under forests in Xishuangbanna.

Prof. CAO Min and his team of Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences investigated the seasonal dynamics of tree seedlings along a mountain transect of the tropical forests in Xishuangbanna. Their aim was to examine the response of tree seedlings in forests on mountains to elevation and monsoon rhymes.

The researchers monitored the seasonal variation of seedling species composition, and their relative growth rate (RGR) along an elevational transect in tropical forests for two years.

The researchers established four elevational bands (800, 1000, 1200 and 1400 m) in the Xishuangbanna National Nature Reserve. On each elevational band, they set up five 20 m × 20 m plots. They calculated the abundance and species richness of tree seedlings in each plot in rainy and dry seasons in both 2014 and 2015 separately.

They observed the highest species richness of seedlings at 800 m and found that tree seedling species richness decreased as elevation increased in both rainy and dry season. There were significant seasonal and elevational differences in soil moisture in two years. They also observed higher soil moisture at 800 m in dry season.

They found significant positive correlation between soil moisture and relative growth rate (RGR) in dry season but no correlation in rainy season. The RGR declined as elevation increased in dry season. Seedling abundance and species richness increased significantly from dry season to rainy season.

The study suggested that seasonal drought can inhibit the growth of seedlings. The more severe and the longer duration of the drought is, the more stress the seedlings will meet and the more leaves the seedlings will shed in order to survive dry season.

 The study entitled “Variant responses of tree seedling to seasonal drought stress along an elevational transect in tropical montane forests” has been published in Scientific Reports.