With their mostly black and white bark, birches are popular ornamental trees for the garden if it weren’t for their pollen count. The blossoming season of the trees is a problem for many allergy sufferers in spring.
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The plant genus Betula includes about 100 species. The most important birch species in Europe are the downy birch (Betula pubescens), the dwarf birch (Betula nana) and the low or tree birch (Betula humilis). The most well-known species is Betula pendula (silver birch, also called silver birch, silver birch or warty birch). It is often planted as an ornamental tree in gardens or along roadsides. It also occurs in mixed forests, but there are also real birch forests. Since Betula pendula is extremely undemanding, it is the most important pioneer tree species in Central Europe and is the first tree to colonize fallow, ruined or bare areas.
The flowering time of the silver birch is in spring. The time of the main flowering is usually in mid-April. The pre-blooming period is late March to mid-April, and the post-blooming period is from mid-April to early June. The birch begins to release its pollen into the wind when the temperature constantly rises above 15 degrees Celsius. This is why the start and end of exposure often differs from region to region.
The flowering period of the dwarf birch lasts from April to May. In Central Europe it has now become very rare. It can still be found occasionally in the North German lowlands, in the Bohemian Forest, in the Ore Mountains and in the Harz Mountains. In Austria, the dwarf birch grows in the southern federal states, in Lower Austria as well as in Salzburg and Tyrol.
The shrub birches also bloom from April to May, but – like the dwarf birch – they are only rarely found in Germany. The highly endangered plant still grows in a few places in the foothills of the Alps and in the North German Plain.
Downy birches, also known as downy birches, broom birches, silver birches or hairy birches, bloom from April to May. They grow on moor and peat soil with a pH value of less than 5. In the Allgäu Alps they can be found up to 1,700 meters above sea level.
Normally, a high pollen count every two years (mast year) can be expected, but a change seems to be in the offing. Because in 2020 the amount of pollen was not only above the long-term average, but also above that of 2019, which had already been classified as high.
Allergy and Symptoms
Birch pollen is highly allergenic. This is how about half of all allergy sufferers react to pollen. The main allergen is Bet v1, named after Betula pendula (formerly Betula verrucosa).
The allergic reaction to birch pollen is often confused with a common cold because the symptoms are very similar:
- Eyes: itchy, red (conjunctivitis)
- Nose: itchy, stuffy or constantly running, fits of sneezing
- swelling of the mucous membranes of the throat
- Narrowing and congestion of the bronchi up to asthma and wheezing
- bad sleep, exhaustion, tiredness
Since these symptoms also appear with other pollen allergies, you should consult a doctor to clarify the cause of the allergy. In this way, a therapy can be initiated that not only provides relief, but also protects the mucous membranes from damage that can occur with severe and recurring inflammation.
An allergy to birch pollen is not only the most common, but also often triggers cross-allergies. This includes allergies that occur due to birch pollen allergy. If the allergic reaction occurs to a food, such as an apple, it is referred to as a pollen-associated food allergy. The most common form of this food allergy is birch pollen-nut-pome fruit syndrome. People who are allergic to birch often develop an allergy to nuts and pome fruit, since birch and rose plants are botanically related. However, the danger also exists with fruits and herbs from other plant families, as the following list shows:
- Birch family: hazelnut
- Umbelliferae: anise, dill, fennel, carrot, coriander, cumin, parsley, celery
- Legumes: Soy
- Nightshade family: chili, tomato
- Lamiaceae: basil, oregano
- Rosaceae: apple, apricot, pear, cherry, almond, nectarine, peach, plum
- Ray pen family: kiwi
- Sumachgewächse: Cashewnuss
- Topfruchtbaumgewächse: Paranuss
- Walnut Family: Walnut
The symptoms of a cross allergy show up quickly. An allergic reaction often occurs after just a few minutes. This can show up as itching or burning in the mouth. Other possible symptoms include swelling of the tongue or buccal mucosa.