Zoology/Biology session

Over the past 100 years, humanity has transformed its environment incredibly. Climate change, the introduction of various non-native species, and the cargoes where organisms travelling as 'stowaways' have led to the arrival of 'invaders' in native communities. In the case of plants, these invasive species have outgrown their native competitors mainly due to their rapid reproduction, wide tolerance and different phenology. In Hungary, the best examples of this are the silkweed (Asclepias syriaca) and giant goldenrod (Solidago gigantea), which were introduced from North America. In our research, we sought to find out whether these two species alter the flowering phenology of a sand bar grassland throughout the year, i.e. whether the invasive plant causes the flowering period of native species to shift. To do this, we used pairs of quadrats, one quadrat with no invasive species present and the other with invasive species providing the main cover. Species were divided into 4 categories: early annuals, early perennials, late annuals and late perennials. The presence of silkweed had a positive effect on the number of flowering buds of several early-flowering perennial species (e.g. Poa angustifolia), while it had a negative effect on many late annuals (e.g. Xeranthemum annuum). This is due to the relatively late emergence and low density of silkweed sprouts, which does not shade out early flowering species but opens up native grassland. Later, however, the invasive species' sprouts shade out the late-flowering species. Giant goldenrod has had a positive effect on the flowering number of many early-flowering species (e.g. Viola arvensis), but due to the high density of the species, it has a negative effect on late-flowering perennial species, especially in the Caryophyllaceae family. Overall, giant goldenrod had an effect on the number of flowering buds of many more species than silkweed. Phenological shift was observed in one case, with Cerastium semidecandrum flowering later due to silk borer. In the case of giant goldenrod, this was not detected in any species.