Ecologists, evolutionary biologists and restorationists are interested in the composition and density of seeds in the soil seed bank and thus many studies have been conducted. However, the lack of consistent guidelines for sampling seed banks remains as an obstacle in making it possible to compare the results of seed bank studies, especially of forests. Dr. SHEN Youxin of Xishuangbanna Tropical Botanical Garden (XTBG) and his colleagues conducted a study at Shilin Stone Forest Geographical Park (24°38′–24°58′N, 103°11′–103°29′E), Yunnan Province, southwest China. They hypothesized that larger soil sample sizes and sampled areas will allow for more accurate determination of the presence and abundance of seeds of woody species in forest soils. 

In the study, a large number of small soil sample (LNSS) and a small number of large sample (SNLS) were taken from a diverse karst forest in Yunnan Province of southern China, and the germination of woody species was determined. Their specific objectives were to: 1) Determine the effectiveness of the LNSS vs. the SNLS strategy in detecting woody-plant seeds in forest-soil seed banks; 2) Analyze the relationship between the number of woody species and sample area; 3) Suggest an appropriate sampling area and size for forest soil seed-bank studies. 

They collected 100 samples that were 10 cm (length) ×10 cm (width) ×10 cm (depth), referred to as larger number of small-sized samples (LNSS) in a 1 ha forest plot, and placed them to germinate in a greenhouse, and collected 30 samples that were 1 m×1 m×10 cm, referred to as small number of large-sized samples (SNLS) and placed them (10 each) in a nearby secondary forest, shrub land and grass land. 

The study found that even with 100 small-sized samples only 13 woody species were found by the LNSS method. The SNLS method captured seeds of all dominant tree species in the standing vegetation.  

Their study confirmed the shortage of conventional large number of small sized samples (LNSS) in detecting seeds of woody species. Their study also demonstrated that seeds of species dominant in the forest stand could be detected by increased total sample areas and sizes such as SNLS. 4 m² might be the first estimation of minimum area for forest soil seed bank studies in a particular forest. The researchers concluded that a large sample area and size were needed for forest soil seed bank studies to detect woody species to ensure low discrepancy with stand forest. 

The study entitled “Large Sample Area and Size Are Needed for Forest Soil Seed Bank Studies to Ensure Low Discrepancy with Standing Vegetation” has been published in PLoS ONE.