干旱区生态环境知识资源中心

The regeneration and patch dynamics of Sarcopoterium spinosum shrubs may have profound effects on rangeland productivity in Mediterranean semiarid shrublands. Yet little is known about the role of the soil seed bank in seedling recruitment of S. spinosum and whether grazing has any effect on the size and spatial distribution of its seed bank and seedling emergence. We studied the effects of sheep grazing on the soil seed bank and seedling emergence of S. spinosum in a Mediterranean semiarid shrubland in the northern Negev Desert in Israel. The variation in density of the seed bank in autumn and of seedling emergence in the spring was measured during two years, beneath shrub canopies and in the open space matrix, inside and outside exclosures that prevented sheep grazing. Seed density beneath the shrubs ranged between 2000 and 3000 seeds m(-2), and was about ten times as great as that in the adjacent open space patches. Moreover, beneath the shrubs, the proportion of the autumn seed bank that emerged as seedlings in the spring was three times as great as in the open space patches. Grazing caused a 60% increase in soil seed bank density beneath the shrub canopy but had no effect on the seed bank in the open space patches. Variation in spring seedling density between grazing treatments and patch types was strongly related to the availability of seeds in the previous autumn.