Pollen is in the Air

Red Alder (Alnus rubra)
Red Alder (Alnus rubra) begins to produce pollen as early as late February on Vancouver Island.

When my husband starts sneezing and snuffling, I know that allergy season has arrived. Here on the coast, pollen related allergies can start in late February and continue through to September. To better understand my husband’s suffering I went to the source, the pollen itself. Most of us are familiar with pollen as the yellow dust that smears our car windshields, or forms a film over spring-shower puddles.

Pollen producing trees, shrubs, flowers and grass are all around us. Pollen, which is always male, is a critical part of plant reproduction. A single pollen grain is actually a male reproductive unit, which scientists call a “male gametophyte”. About three cells large, a single grain of pollen is visible only with a microscope. The familiar yellow dust is made of millions of individual grains. Through the spring we live and breathe pollen, which gets into our hair, clothing and nostrils.

Red Alder (Alnus rubra) Catkins
The male catkins of Red Alder (Alnus rubra).

Trees are the culprits of most pollen. The first wave comes from red alder, which starts in late February and peaks in mid-March. Red alder is a fast growing leafy tree with red inner bark. Alders have clusters of separate male and female catkins on the same tree. Male catkins are narrow and drooping and are 10-15 cm long at flowering time. Each catkin is packed with miniature male flowers producing thousands of pollen grains. Catkins that have fallen on the ground often have a yellow halo of pollen around them. Spring female catkins are smaller, greenish and less noticeable.

Alders rely on wind for pollen dispersal. The pollen drifts through the neighbouring trees and lucky grains land on the female catkins. This is a hit and miss process so a lot of pollen goes to waste, which is why red alder produces a tonne of the stuff. By the fall, the mature female seed catkins become brown and woody, and each contains 50 to 100 seeds.

Douglas-fir (Pseudotsuga menziesii ssp. menziesii)
The male pollen cones of Douglas-fir (Pseudotsuga menziesii ssp. menziesii).

The next barrage of pollen comes from the conifers, trees with evergreen needles. The most prevalent conifers in our lowland areas are Douglas-fir, Sitka spruce, western hemlock, western red cedar, grand fir and shore pine. The Douglas-fir, like most conifers, has male and female cones. The brown, scaly “fir cones” that most of us are familiar with are the mature female, seed bearing cones. Male cones are much smaller. At maturity these are rusty-red and crispy, and easily found on the forest floor. All conifers use wind for pollen dispersal, and pollen sifts through a 5-10 tree radius. At the time of pollination (the end of March for Douglas-fir), the female cones are soft, green and sticky, providing a suitable landing pad for pollen.

Later in the spring, trees have finally finished shedding vast amounts of pollen. But this is, unfortunately, not the end of allergy woes. Next, arising from roadsides and fields, is the grass pollen. Most of us don’t think of grass as having flowers, since they are not showy or colourful and are greenish and non-descript. Grasses, like many trees, rely on the wind to blow pollen where it needs to go. Species of grass bloom at different times, from spring through late summer.

During the summer many plants have dried up and the allergy sufferer can expect some relief. But what about all of those colourful, blooming flowers? Flowers, shrubs, and trees such as apple, maple and oak have an entirely different system of pollination. Unlike red alder, conifers and grasses, they don’t rely on the hit-and-miss air-bourne method to disperse pollen. They use insect pollinators, such as bees and butterflies. Insects are drawn to attractive flowers for the purpose of getting nectar. While the insect is sucking up the nectar, it gets a dusting of pollen, and unknowingly deposits it on the female part of the next flower visited. Due to the accuracy of this method, a lot less pollen is produced and needed than with wind pollinators. All the flowers in the garden produce just a fraction of the pollen produced by one alder tree. The wind pollinators, especially trees, pack the biggest punch for allergy sufferers.

About the Contributor:

Jocie Brooks is a naturalist and writer based in the Comox Valley, Vancouver Island, British Columbia.