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  By Harvey Thommasen, with Photography by Nick Didlick In early spring, the coastal valley bottoms on the northwest coast of Canada, take on a purplish glow from swollen catkins hanging from the outer branches of alder, birch, hazelnuts, and sweet gale. Walking to the stream, anticipating an early season cutthroat, perhaps feeding on the first emergent salmon fry, an angler can be forgiven for feeling light headed. Maybe it’s the anticipation of the fishing season ahead - or maybe it’s effect of one of nature’s great events. When a wind stirs.
If you could capture the air this time of year, and look at it under the microscope you would find that the sky is full of trillions of pollen particles belonging to various conifer trees and to flowering plants like the alders, trembling aspens (Populus tremuloides), black cottonwoods (Populus trichocarpa), paper birch (Betula papyrifera), and the various willows (Salix spp) found in the valley. Later in the season (typically May, June and July), pollen from grasses, sedges, stinging nettle (Urtica dioca, sea plantain (Plantago maritima), sour grass (Rumex acetosella), western Dock (Rumex occidentalis), and crowberry (Empetrum nigrum) fills the skies. By knowing when in the year hay fever-like symptoms (eg runny nose, itchy eyes) arise, you can guess which kind of pollen allergy the unfortunate person suffers from. People with tree pollen allergies will experience symptoms in March and April, while those with grass pollen allergies will experience symptoms in May, June, and July. Like all sexually reproducing organisms, plants have a male-like reproductive organ and a female-like reproductive organ. In the conifers (gymnosperms), the male-like reproductive structure is called a microsporangiate, and the female-like reproductive structure is called a megasporangiate. Microsporangia produce pollen. Megasporangia produce the immature seed, and when mature these structures are easily recognized as cones. In the "flowering" plants (angiosperms), the male-like reproductive structure is called a stamen, and the female-like reproductive structure is called an ovary. Stamens produce pollen, while ovaries produce ovules or immature seeds. Pollination, refers to the transportation of pollen from the male-like reproductive organs to the female-like reproductive organs. In wind pollinated plants, the wind transports the pollen from the male-like
Studies have shown that wind can carry pollen particles to altitudes of 5800 metres (about 19,000 ft), and as far away as 400 kilometers (250 miles) from its plant of origin. As you might guess, the odds that a single pollen particle will reach an ovule or female conifer cone by wind transportation is very low. A pollen particle is far more likely to fall onto the ground, be stranded on another plant, or be blown into the ocean, the river, or a lake or pond. To improve the odds, wind pollinated plants employ a number of strategies. Firstly, wind pollinated plants tend to grow together in vast continuous tracts. In the Pacific Northwest, conifers dominate the mountains, sedges dominate tide flats, grasses dominate coastal meadows, alders dominate avalanche chutes and cut over lands, while black cottonwood, aspens, willows, and birch dominate riparian zones. All these plants are wind pollinated. Secondly, each plant produces tremendous amounts of pollen. For example, each sour grass flower cluster produces an estimated 400 million pollen grains. Conifers release so much pollen in April, May and June one can easily see a layer of yellow dust on the ground, and yellow scum on the water. The more pollen a plant can release to the skies, the greater the odds that one of the grains will be fertilize an ovule or conifer cone. Thirdly, wind-pollinated broad-leaved trees and shrubs (eg alder, cottonwood, aspen, birch, willow) produce their flowers (catkins) very early in spring before leaves are out. This ensures that pollen will not be intercepted by foliage. Wind-pollinated grasses, sedges, and forbs employ a similar strategy in that they grow fast, and release their pollens before other plants have a chance to grow up and block transfer of pollen. Fourthly, wind-pollinated flowers are simple in construction. There are no petals, or other flower parts to get in the way of the pollen and unfertilized seed. These flowers are designed to catch pollen, not to attract pollinating animals.
Lastly, wind-pollinated flowers tend to be widely distributed over the plant, and not concentrated in one given area. These plants also tend to separate male and female sexual structures from one another. In conifers, for example, female reproductive structures tend to occur at the end of a branch, while the male structures tend to occur more proximally. Again, these are strategies designed to maximize the odds that fertilization between different plants will take place, and to minimize the odds that self-fertilization will occur. |
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Wind pollination works best in areas where there is dependable wind. Coastal valleys of the Pacific Northwest are well suited to wind pollination. Winds blow almost every day of the year. From late autumn to early spring, winds are predominantly from the southeast to southwest as air circles counter clockwise over the Central Coast around Aleutian Low Pressure systems. From late spring to early autumn, the Aleutian Low Pressure systems weaken, and so coast winds are predominantly from the northwest as air circles clockwise over the Central Coast. These winds pick up the pollen, and carry it over over vast forests of conifers, alders, willows, cottonwoods, and over vast tracts of sedges on the tideflats, and over large grassy meadows. 
