Tree Pollen Levels during Two “Very Strong” El Niño Events

Abstract

We anticipated that the very strong el Niño of 2016 would be a factor in boosting local tree pollen levels as recorded during el Niño1998. Daily 24 hour Burkard spore trap samples from mid-March to mid-June of 1998 to 2016 were analyzed for tree pollen content. Meteorological factors were examined to explain the large difference between the 1998 & 2016 tree pollen counts. (1) Total tree pollen levels in 1998 were the highest recorded in SW Ontario, while the 2016 levels were the lowest. (2) We did not find a correlation between weather factors (rainfall & growing degree days) and the two “very strong” El Niño events. (3) Local tree pollen levels have dropped substantially after a peak in 2010. El Niño is a recurring global climatic phenomenon resulting from changes in oceanic surface temperatures that affect weather. Very strong El Niño events occur approximately every 15-20 years. In 1998, local pollen production was elevated for almost all the deciduous trees with very high levels of Juniper/Cedar. The literature indicates that annual pollen production is primed by precipitation in the previous year and the season is initiated by temperature (growing degree days). We found such relationships inconsistent and did not explain the two El Niño “seasons” or the recent drop-off in recorded tree pollen production.