Temporal variations and spatial differentiation in the black alder and silver birch pollination pattern-the impact of local climate or something more?

- Black alder and silver birch pollination phenology was examined.
- Spatial and temporal variability in the timing of pollination was stated.
- Pollination pattern was presented against the background of local climate.
- Thermal conditions did not clearly affect spatial diversity of pollination patterns.
- Phenotypic plasticity may be a cause of the diversity among and within populations.

Numerous abiotic factors have an important impact on the phenology of woody plants with temperature as the main driver of their development. Furthermore, the biological factors connected with phenotypic plasticity and genetic heterogeneity might be the cause of differentiation in phenological response to abiotic factors. As objects of our study, we chose black alder and silver birch trees. The main aims of the study were to demonstrate the spatial and temporal diversity in the timing of Alnus glutinosa and Betula pendula pollination as well as to identify factors affecting these variations. We focused on abiotic factors such as thermal conditions: air and surface temperatures, within and between population variability. Phenological observations were carried out in Rzeszów (SE Poland) in a period of four years at over a dozen locations. Stands differed in their thermal conditions and prevalent land use types. The pollination pattern in the study area was presented against the background of local thermal conditions which were described by Land Surface Temperature (LST) and maximum daily air temperature. LST was estimated with a single-channel algorithm using satellite images obtained from Landsat 7 and 8. Our results showed great spatial and temporal diversity in the pollination pattern in the study area. Year-to-year variations in the B. pendula pollination pattern were less pronounced than in the case of A. glutinosa. The pollination pattern was strongly influenced by temperature before and during pollination. In the study area, the variability of LST was greater than that of air temperature but the relationships between the timing of pollination phenophases and LST or land use types were weak. It was observed that the same sites were similar in their pollination pattern − the timing of phenophases was 'accelerated' or 'delayed' during the whole study period. The same individuals were the first or the last that began to pollinate independently of the year. We concluded that despite the impact of temperature on A. glutinosa and B. pendula development, the phenotype of an individual tree might be as important for phenological variability as local climate.