Pollen in Abundance: A Stress Crop?

Observation by Katrina Forrest:

There has been an abundance of pollen this spring in Victoria, British Columbia. In one day it falls thick enough to provide full ground cover (Figure 1), and can turn anything yellow in a matter of hours (Figure 2). The pollen clouds have been so thick that they resemble smoke and people without pollen allergies have been complaining of gritty and painful eyes.

In times of drought, trees often drop a crop of stress cones (Westfall & Ebata, 2018). This abundance of pollen could be a similar phenomenon, an increased rate of pollen dropped due to the multi-year drought trend (British Columbia Drought, n.d.), resulting in stressed trees overachieving pollination. The increased dispersal of pollen could also be a reaction to higher temperatures as “pollen dispersal might allow plants to survive a faster rate of climate change” (L.C. et al., 2016, p. 10728). It would appear that drought causes pollen to dehydrate, which diminishes the spores to only a few cells (Pacini, & Dolferus, 2019) which would in theory reduce the amount of noticeable pollen, further lending to the idea that more pollen has been produced this year.

Also to be considered is the unprecedented amount of rain this January: 262.2mm (Rainfall, n.d.). The high precipitation would have been a much needed respite from the multi-year drought, however, British Columbia is again experiencing unusually low precipitation for spring, returning the ecosystem to drought again. Perhaps the high rain volume in January helped produce larger yields of pollen this spring, or simply helped to hydrate the gametophytes before the resumption of drought.

The prolonged drought of British Columbia is the result of larger ecological changes to the climate (Natural Resource, n.d.). With greatly increasing global temperatures since the industrial revolution, drought is one of the common effects felt in many areas. Drought is already common in Western Canada (Natural Resource, n.d.). It could be that the increased dispersal of pollen is a last stand for the stressed trees unlikely to do well in increased temperatures. This can be seen already in trees like the red cedar (which are known to be drought sensitive). It could also be, as L. C. et al. (2016) explain, that the higher yields lead to better adaptation to higher temperatures.

Wouter Willem Cleef is a tree preservation coordinator for the city of Victoria. He works with tree preservation in the local area and will has an understanding of stressors and stress reactions to drought. He is also involved with community food security and pollinator giving him excellent place-based knowledge. Cleef suggests that this may be a usual amount of pollen, but that a lack of rain has left the pollen in the atmosphere and it has not dissipated into the soil etc. as usual. This leaves it to blow around on the surface where it is more noticeable than usual (Cleef, personal correspondence, 2020, April 19).