The Importance of Small-Scale Disturbance for Seedling Establishment in Cirsium Vulgare and Cynoglossum Officinale

Abstract

(1) Germination and establishment of Cirsium vulgare and Cynoglossum officinale in various micro-environments were studied in a sand-dune area at Meijendel, The Netherlands. (2) The number of established seedlings was increased forty-fold in Cirsium vulgare and five-fold in Cynoglossum officinale by artificial speed input of 11 seeds dm-2. In Cirsium vulgare, seed input was the primary prerequisite for seedling emergence. Disturbance of soil and vegetation alone had little effect on the number of seedlings establishing naturally, but increased the number of seedlings in plots with seeds sown. (3) Disturbance had the additional effect of advancing the germination period and accentuating autumn germination in Cirsium vulgare. (4) Seedling mortality did not differ between disturbed and undisturbed plots. In both species seedling recruitment was high in thickets and Crateagus scrub and low in open vegetation. (5) After seed sowing, significantly less seedlings were found in May and July on sites where the naturally occurring population had disappeared (Cirsium vulgare) or dropped to a low density (Cynoglossum officinale) than on sites where the natural population still thrived. These differences were not found (Cynoglossum officinale) or reduced (Cirsium vulgare) on disturbed plots with seeds sown, indicating the importance of small-scale disturbances for population maintenance.