Reproduction and population structure of Primula veris L. (Primulaceae) in semi-natural grasslands – a landscape and management perspective

The large number of threatened species, both insects and plants, in the European agricultural landscape, has often been attributed to the abandonment of semi-natural grasslands. Species may also be threatened in the remaining managed grasslands due to a changed and intensified management, compared to the historical use. In this study, effects of grazing management and population characteristics were examined in terms of their importance for the seed production and recruitment of the perennial herb Primula veris L. Four different life-cycle events related to reproduction were studied in 31 and 28 populations, in 2003 and 2004, in an 11 km landscape in Sweden. Population structure was examined in 11 populations in 2004. The losses of propagules in total and at each life-cycle transition were calculated. The results showed that high proportions of propagules were lost due to unsuccessful pollination, grazing, and unsuccessful establishment of seedlings. No single explanatory variable could consequently determine the unsuccessful pollination both years. Grazed areas had higher proportion seedlings compared to other life stages, but not higher density of seedlings compared to ungrazed populations. Ungrazed populations had, compared to grazed areas, equal seedling densities, equal densities of juvenile plants, but higher densities of vegetative plants. Thus, the reduced seedling recruitment per seed in ungrazed grasslands was compensated by a higher production of seeds. Conversely, the loss of seeds in grazed areas was compensated by a higher seedling recruitment per seed. To combine the positive effects of low litter layers and high seed set the results from this study add to the increasing number of studies which indicate that extensive and site specific grazing regimes have to be included in the management of semi-natural grasslands to maintain or enhance the diversity of both rare plants and host plants for rare insect species.