Differences between airborne pollen and flowering phenology of urban trees with reference to production, dispersal and interannual climate variability

Annual totals of daily arboreal pollen concentrations were analysed in Mar del Plata (Argentina) during 1993 and 1994. Flowering patterns were associated with timing and intensity of pollen appearing in the air. Seasonal climatic parameters before the start of flowering and current weather conditions during dispersion were considered. Flowering showed a regular pattern between years and it could be defined by cumulated pollen percentages. Arboreal pollen counts were higher in the first year and is probably due to 1) better climatic conditions connected with pollen productivity and 2) lower precipitation after pollen emission. Betula and Q. ilex showed an opposite behaviour that appears to be caused by a biennial fluctuating rhythm of pollen production.