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Where is spring and the pollen allergy season?

We hear it all the time. When will winter be over? Well not only are people saying it but so are the trees.

This winter the March weather has been very cold with lots of snow. April has begun with very cold temperatures as well and the temperatures are warming up very slowly. The sampler at our site in Ottawa on April 6th is still surrounded by snow. The winter snow cover is good for the trees since it provides protection for them during the cold winter months. What they don’t like is a stretch of warm weather in the spring followed by a cold snap for several days or even weeks. This can fool the trees into budding and it can have a profound effect on the pollen season to the point of almost eliminating it if the trees have started budding. We don’t have that problem this year so far.


The trees are affected by more than just winter and spring weather. The pollen is formed by the trees in the weeks following there pollen season for the next year. So whatever happens at that time also has an impact on how much pollen reserve is available for the season next year. If it is a very hot dry period or a cold wet one it will determine how much pollen the trees form for the next season.

I have taken pictures of the early pollinators the maple and the cedars. They are not even slightly close to being ready to release their pollen. A few days of warm temperatures could change that. The birch trees, the late pollinator, have a while to wait until the weather provides them enough heat for their pollen season to begin. There are stages of when different trees produce their pollen. We have the early pollinators like the maples, the alder, elm, cedars and the poplars. The group of later pollinators consist of the oaks, the ash, the birch and the pine group. There are other trees that fit in each of these groups but they can be different for each site.


Since the field of Aerobiology is its infancy we are still studying the impact of weather on the pollen seasons from year to year. We knew early in March that 2014 going to be a late season and it has been. When figuring out when the trees are going to be releasing their pollen we take into account several parameters. These include matching weather seasons to previous years. This is a long process and needs a great deal of pollen and weather data. So for predicting the beginning of each season we use the current weather data for temperature, rain and sunshine. These are the most important and easily used indicators.

Sampler in Ottawa (Large)
Sampler in Ottawa

So this year is proving to be late in starting but we have to see what the weather holds out before being able to say what is going to happen. Since the season is starting late the group of early pollinators will probably try and release their pollen quickly which has a potential of creating a shorter pollen season.

The fungal spores which consist of many important allergens are similar to the trees in that they have their own seasons as well. They are always generally low during the spring months when the trees are releasing their pollen. So they take their turn later in the season and closer to the warmer spring and summer months. Fungal or mold spores are affected by weather as well. Rain, Temperature, sun and wind impact the types of fungal spores released in the air. One of the types of spores that are released in the summer months is Coprinus which is a mushroom often seen growing on people’s lawn.

Coprinaceae or inky cap mushrooms
Coprinaceae or inky cap mushrooms

One of the most commonly known fungal spores is Cladosporium which is released for longer periods than others from spring to fall. This fungal spore occurs on dead grasses and often on the residual structures from the trees after the pollen season is finished. The poplar fluff that is often seen is large amounts after the season can have copious amounts of this fungal spore and can cause allergic reactions.

When thinking of allergic reactions at this time of the year one has to consider air quality both indoors and outdoors along with outdoor allergens and pollution.


Written by Frances Coates from Aerobiology

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