Heat and chill requirements of Fraxinus flowering in Galicia (NW Spain)

Fraxinus pollen data from eight Galician localities (1999-2003), recorded using 7-day Lanzoni VPPS pollen traps, were studied to determine their temporal and spatial distribution. The determination of the chill and heat required to trigger flowering and the start cumulative date were calculated using ten years of pollen data from Ourense. The sum of maximum temperatures from the 55 days before the peak date showed the lowest standard deviation coefficient and the mean quantity of accumulated heat was 741. Temperatures below 0°C and/or rainfall at the beginning of flowering caused a longer period before the peak date was registered. Temperatures recorded in November were very important for chill accumulation and determine the heat requirement needed to trigger Fraxinus flowering in Galicia.