March is a period of marked increase in alder pollen levels in Poland. Although the tree begins to release pollen as early as January, it is in March that pollen concentrations in the air most often reach their highest levels. As the first warmer days arrive, large quantities of pollen are released into the atmosphere, which for many allergy sufferers marks the start of the spring allergy season. The alder is a wind-pollinated plant, which is why its pollen spreads easily through the air and can be carried over long distances.