Soil diaspore reserves above the timberline in the Austrian Alps

Soil diaspore reserves are considered to support self-healing processes after vegetation disturbances. Therefore, the stratified reserves of viable diaspores in superimposed soil layers of four sites above the timberline in the Austrian Alps were assessed. At each site, a semi-natural (“undisturbed”) extensive alpine pasture and the disturbed vegetation on hiking trails were investigated. Eighty soil cores in total (corresponding to 400 slices, each representing a 1-cm layer between 0 and 5 cm depth) were taken in autumn and subjected to germination tests after vernalization. The total diaspore numbers in disturbed and undisturbed plots did not differ significantly, but all undisturbed soils contained higher species numbers than disturbed ones. Seed shape and size clearly influenced the vertical distribution. Intact soils showed a significant decrease in big/long diaspores with increasing soil depth. Disturbances influenced the aboveground species composition and therefore the distribution of seeds of different size. In case of disturbances, the restriction of most big seeds to superficial layers means a threat for small populations of rare and protected species such as Viola lutea subsp. sudetica with relatively big seeds near the soil surface. When the disturbances stop, the diaspore communities might initiate a first, but with respect of landscape protection and preservation of species diversity insufficient step of vegetation restoration.