The use of the pheno-climatic model for forecasting the pollination of some arboreal taxa

Air temperature is one of the most frequent parameters for the application of pheno-climatic models which can give information for the forecasting of the beginning of pollination of various species. For the present study 12 years of aerobiological monitoring data concerning the pollination of hazel, alder, elm, poplar, and willow have been employed to forecast the beginning of their pollination assuming that the beginning of pollination of one species corresponds to a specific moment of phenological development for another species with later pollination. The difference expressed in days between the pollination of two winter taxa with successive flowering is very variable. If this interval is expressed in terms of heat (summation of mean daily temperature above a certain threshold) the differences are smaller. The delay between the pollination of alder and elm varies between 3 and 21 days depending on the climatic trend, but during this period elm on average accumulates 26 degree-days (base temperature 4°C) with a lesser variability. In this way we can begin to calculate the heat requirement for elm from the beginning of alder flowering. This application can be used for other couples obtaining statistical values which are more significant than those obtained with the phenological model, with the exception of willow. The results indicate that for the majority of the species with winter flowering there is a linear relation between the flowering dates and air temperature.