Spatial and temporal variability of seed bank resulting from overgrowing of xerothermic grassland

Abstract

The aim of my study was to determine changes in the seed bank and vegetation during the process of overgrowing of the xerothermic grassland situated on the slopes of the White Mountain (349 m a. s. l., the Central Roztocze Region, South-Eastern Poland). I also examined whether the changes of vegetation can be predicted if we know the structure of the burned seed flora. To achieve this goal I used two sets of data: one collected from three different environments (grassland, brushwood and woodland) at the same time (toposequence), and the other collected twice from the same place at the interval of seven years (chronosequence). I stated that the appearance of even a small number of ornitochorous seeds and their seedlings can be treated as a signal that the bush encroachment will accelerate. Seed number seems to decrease during succession in the analysed sequence of plant communities. The total number of species in the seed bank did not change in the most dynamic plant communities: grassland and brushwood, and it was significantly higher there than in the seed bank of woodland. During the time of observation, the most important quantitative and qualitative changes took place in grassland vegetation, which is more similar to brushwood vegetation now than it was at the beginning of the study.

Germinable Soil Seed Bank in Biancana Badlands

“…The germinable soil seed bank showed a less aggregated spatial pattern. These results agree with the findings of Bossuyt and Honnay [10], Czarnecka [50], and Hanlon et al [67], who found greater similarity in seed bank composition than in the corresponding standing vegetation. Contrary to previous findings [10], the similarity between the seed bank and standing vegetation was lower for pioneer grassland than for other grasslands.…”

“…Grasslands and overgrown grasslands showed similar soil seed bank compositions and did not differ in the number of seedlings or recorded species. Encroachment of grassland by spontaneous succession or afforestation generally causes a decrease in the number of grassland species in the soil seed bank [50][51][52]. Our results seem to differ from the latter studies, while agreeing with those of Milberg [53], Kalamees and Zobel [54], Maccherini and De Dominicis [8], and Bossuyt et al [52], who failed to find any substantial changes in seed density or composition with grassland succession, at least in the early stages.…”

The dynamics of the population of a steppe perennial Senecio macrophyllus M.BIEB. during xerothermic grassland overgrowing

“…That process was confirmed by J. Czarnecka (2008) along the transect leading through three adjacent communities in the close vicinity to my study area: woodland, brushwood and grassland. The other noticeable change was overgrowing of low and loose xerothemic grassland by meadow and ruderal species, mainly Brachypodium pinnatum and Calamagrostis epigejos, which limited small-scale gaps named safe sites (Harper 1977), regenerative niches (Grubb 1977) or space free from competition (Bullock 2000) necessary for seed germination and seedling establishment.…”

“…3: 247-256, 2009 253 ACTA SOCIETATIS BOTANICORUM POLONIAE Czarnecka J. 2004Czarnecka J. , 2008. Therefore, the sufficiency of permanent flux of propagules is of great importance in species that do not form a persistent soil seed bank like S. macrophyllus.…”

“…For the next long period (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) the ramet dynamics exhibited an oscillation type, and the proportion of immature vs. mature plants was more balanced and typical for a population in the phase of fluctuation growth. The percentage of juveniles changed significantly (U-test; 0.0001<P<0.05), except some cases between the consecutive seasons during the study periods: 1995, 2001-2003-2008. Since 2004 to the end of the study the lack of juvenile genets recruitment was reflected in the dramatic decreasing of the population numbers.…”