Shading results in depletion of the soil seed bank

To what extent is the decline of characteristic dry alvar species related to the decline in the soil seed bank during scrub encroachment? We recorded the number of flower stems in the vegetation in relation to light attenuation along an encroachment series progressing from open alvar through small gaps inside dense scrub of Juniperus communis (cover of 60%) to intact dense scrub (cover of 100%) on the island of Öland, Sweden. This measurement of potential reproduction (number of flower stems) was then compared to the number of species in the soil seed bank at each site along the alvar encroachment series. Scrub encroachment results in light attenuation between and under the shrubs. The total number of flower stems averaged over all species was similar between gaps and open alvar, but that of alvar species was significantly lower in the gaps, indicating that light attenuation could reduce their seed set. Shading in gaps is related to depletion of the soil seed bank and loss of alvar species, particularly those that do not form a persistent soil seed bank.