Seedling Establishment of the Biennials Cirsium Vulgare and Cynoglossum Officinale in a Sand-Dune Area: The Importance of Water for Differential Survival and Growth

Abstract

(1) Seedling mortality of the biennials Cirsium vulgare and Cynoglossum officinale was studied in a sand-dune area at Meijendel, The Netherlands. In both species seedling survival was positively correlated with the water content of the top 10 cm of the soil. Early seedling survival (April-May) in Cynoglossum officinale was also positively correlated with the cover of shrubs and trees. Soil water content and cover of woody plants explained 74% of the variance in the early mortality of Cynoglossum seedlings. (2) Throughout most of the year the water content of the top 10 cm of the soil was highest in thicket and lowest in open vegetation. Below 10 cm the rank order of the vegetation types with respect to soil water content was not consistent, and the total soil water potential was always above the critical level for water uptake by the plant. (3) Artificial watering increased seedling survival and growth in the two species, especially in open vegetation. Vegetation types differed with respect to seedling survival but these differences were greatly reduced by the addition of water. It is likely that variation in rainfall causes yearly differences in survival and growth in the two species and affects their distribution over shaded and exposed habitats.