Succession is a key factor in vegetation dynamics. “Successional distance” can be simplified by the state difference between the vegetation of the seed source and recipient. Adding propagules (source) to a degraded site (recipient) is a common way of manipulating secondary succession to restore diversity and services formerly provided by forests. However, no study has considered the effect of successional distance of the source and the recipient site on recruitment and restoration.
Dr. SHEN Youxin and his colleagues of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study at Shilin Stone Forest Geographical Park (24°38'-24°58'N, 103°11'-103°29'E), Yunnan Province, southwest China, a karst geo-park famous for rugged limestone landscapes. They replaced surface soils at an earlier successional stage with soils from one to three later successional stages. By monitoring germination and seedling survival, they sought to answer the two questions: 1). Does the soil source from a later successional stage favor the establishment and abundance of plant communities at earlier successional stage recipient sites? 2).Does the successional distance between the soil source and recipient site affect seed germination and seedling survival?
Four sites in the Shilin karst area of SW China were treated as different states along a secondary successional sere: grass, shrub, young secondary forest, and primary forest. Ten 1 m ×1m soil quadrats in the grass, shrub and young forest sites were replaced with 10 cm deep soil sources from corresponding later successional stage(s) in January 2009.
Their study found that soil seed banks in forests in karst areas in SW China, together with their soil substrates could provide woody seedlings for initiating species turnover of degraded forest land. The successional distance between the stage of soil source and the stage of recipient site strongly influenced seed germination the first year and seedling survival the second year. Soil sources from secondary forest could satisfy the need for successional manipulation. Their results also implied that restoration designs should consider transition threshold states and environmental factors, such as light and soil water. Restoration success at secondary forests could be improved by the implementation of open canopy windows to increase light illumination, and success at grass lands by adding water since both light and soil moisture will affect germination and seedling survival.