Common snowdrop as a climate change bioindicator in Czechia.

The phenological response to climate change differs among species. We examined the beginning of flowering of the common snowdrop (Galanthus nivalis) in connection with meteorological variables in Czechia in the period 1923-2021. The long-term series were analyzed from phenological and meteorological stations of the Czech Hydrometeorological Institute (CHMI). Temporal and spatial evaluation (using Geographic Information System) in timing of beginning of flowering (BBCH 61) of G. nivalis was investigated under urban and rural settings. Furthermore, the detailed analysis of selected meteorological variables to onset of G. nivalis flowering was performed. Moreover, the trends (using Mann-Kendall test) and Pearson's correlation coefficients between phenological phase and meteorological variable were calculated. The main finding of this study was that the trend of the beginning of flowering of the common snowdrop during the studied period (1923-2021) is negative, and it varies in urban and rural environments. The results showed most significant acceleration of the beginning of flowering of G. nivalis by - 0.20 day year-1 in urban area and by - 0.11 day year-1 in rural area. Above that, a major turning point occurred between 1987 and 1988 (both, in phenological observations and meteorological variables), and the variability of the beginning of flowering is significantly higher in the second period 1988-2021. On top of, the study proved that the beginning of flowering of G. nivalis closely correlated with number of days with snow cover above 1 cm (December-March) at both types of stations (urban and rural), and with mean air temperature in February, maximum air temperature in January, and minimum air temperature in March. The Mann-Kendall test showed a reduction in the number of days with snow cover above 1 cm (December-March) during 99 years period at Klatovy station (a long-term time series) by - 0.06 day year-1, i.e., by - 5.94 days per the whole period. Conversely, air temperatures increase (maximum and minimum air temperature by 0.03 °C year-1 (2.97 °C per the whole period) and average air temperature by 0.02 °C year-1 (1.98 °C per the whole period)). Thus, our results indicate significant changes in the beginning of flowering of G. nivalis in Czechia as a consequence of climate change.

Present-day vegetation helps quantifying past land cover in selected regions of the Czech Republic.

The REVEALS model is a tool for recalculating pollen data into vegetation abundances on a regional scale. We explored the general effect of selected parameters by performing simulations and ascertained the best model setting for the Czech Republic using the shallowest samples from 120 fossil sites and data on actual regional vegetation (60 km radius). Vegetation proportions of 17 taxa were obtained by combining the CORINE Land Cover map with forest inventories, agricultural statistics and habitat mapping data. Our simulation shows that changing the site radius for all taxa substantially affects REVEALS estimates of taxa with heavy or light pollen grains. Decreasing the site radius has a similar effect as increasing the wind speed parameter. However, adjusting the site radius to 1 m for local taxa only (even taxa with light pollen) yields lower, more correct estimates despite their high pollen signal. Increasing the background radius does not affect the estimates significantly. Our comparison of estimates with actual vegetation in seven regions shows that the most accurate relative pollen productivity estimates (PPEs) come from Central Europe and Southern Sweden. The initial simulation and pollen data yielded unrealistic estimates for Abies under the default setting of the wind speed parameter (3 m/s). We therefore propose the setting of 4 m/s, which corresponds to the spring average in most regions of the Czech Republic studied. Ad hoc adjustment of PPEs with this setting improves the match 3-4-fold. We consider these values (apart from four exceptions) to be appropriate, because they are within the ranges of standard errors, so they are related to original PPEs. Setting a 1 m radius for local taxa (Alnus, Salix, Poaceae) significantly improves the match between estimates and actual vegetation. However, further adjustments to PPEs exceed the ranges of original values, so their relevance is uncertain.