Seed bank persistence of clonal weeds in contrasting habitats: implications for control

Abstract

The ability of weeds to form a seed bank is important for their population dynamics and management because it provides a refuge enabling reinvasion after established target plants have died. However, knowledge of the differential seed behaviour of individual species over multiple years and varying environmental conditions is surprisingly rare but necessary for effective control of diverse weed populations. We established a seed burial experiment in alpine habitats differing in management regime (i.e., forest, hay meadow and pasture) to determine whether seeds of the unpalatable perennial weeds, Veratrum album (white hellebore) and Gentiana lutea (yellow gentian) were able to delay germination and remain viable over 3 years. Our study shows that both species formed a short-term persistent seed bank; in the third-year, the soil seed banks of both species were nearly depleted, having declined to < 5% of their original size. Both species had strikingly different germination strategies: G. lutea seeds mainly germinated in their first-year, whilst the majority of V. album seeds germinated in their second-year. The fraction of dormant G. lutea seeds increased with seed age, indicating that seeds remained viable after forgoing germination in the previous year. Habitat-specific differences in seed germination increased with seed age, with germination fractions being lowest in moist hay meadows. This suggests that the negative effects of anoxic conditions became more pronounced as seeds aged in hay meadows. Conversely, seed dormancy was equal among habitats. The absence of a long-term persistent seed bank has important implications for the management of both nuisance and endangered-plant populations. In the case of V. album and G. lutea, re-colonization of habitats from the seed bank is unlikely after established plants have been removed.

Life‐History Variation in Contrasting Habitats: Flowering Decisions in a Clonal Perennial Herb (Veratrum album)

“…Hay meadows are mowed yearly before the majority of Veratrum individuals are able to set seed; individuals at the edge of these populations, however, are often not mowed and so set seed (E. Hesse, personal observation). Forests and pastures generally occur on slightly steeper slopes and higher altitudes compared with hay meadows; the altitudes of the study populations range from 1,020 to 1,555 m above sea level (Hesse et al 2007). Populations found in forests are generally smaller than those found in grasslands but contain at least 200 shoots.…”

“…As the rhizome progressively decomposes from its base, branching will eventually produce a number of separate, genetically identical shoots (Kleijn and Steinger 2002). Seed set is highly variable but can easily exceed 1,000 seeds per inflorescence (Hesse et al 2007). Seeds possess small winglike structures and are retained in dehiscent pods until they are dispersed by wind in late autumn, winter, or spring.…”

“…Seeds germinate from April to August bearing only a cotyledon and produce their first real leaf in the following growing season. There is little evidence of a long-term persistent seed bank, but seeds can delay germination for up to 2 years (Hesse et al 2007). Inflorescences are attacked by a range of insect herbivores (Schaffner et al 2001); in western Europe, however, the main insect seed feeders are Eupithecia veratraria larvae, which can greatly reduce seed production over the season (U.…”

“…We conducted a field study in 15 Veratrum populations located in five different valleys in the Swiss Pre-Alps (see Hesse et al 2007); all valleys were located within a 3-40-km distance range. Within each valley, the fate of individuals was followed in three populations situated in ecologically distinct habitats, which were separated !2 km from one another: Picea abies dominated forests, hay meadows, and extensively grazed pastures ( study n p 5 populations per habitat).…”

“…In this species, flowering ramets produce both seeds and asexual offspring. Seeds have limited dormancy and are able to form a shortterm persistent seed bank depending on the habitat (Hesse et al 2007). Veratrum inflorescences are attacked by a suite of native insect herbivores (Schaffner et al 2001).…”