Tree Pollen and Allergy
Tree pollen may trigger allergic rhinitis, or a runny nose, hay fever and red, itchy eyes and these symptoms usually occur seasonally. Symptoms to tree pollen are most often seen in springtime but may occur during the summer and autumn months. There are exceptions to this rule as the cypress tree begins its pollinating cycle in midwinter. Trees that produce abundant light, wind pollinated pollen grains like plane, oak, olive and cypress are all allergenic trees. This group of allergenic trees are predominantly alien trees that have been introduced to South Africa from the Northern Hemisphere and many of our cities have been planted with these trees. Typical species for parks, roadsides and play schools are: oak, plane, cypress and olive trees. Most of our naturally occurring or indigenous trees are pollinated by birds, insects or small mammals, like bats or mice. The indigenous trees usually produce large, colourful flowers with heavy, sticky pollen that does not remain in the air for long periods and for this reason the pollen of our indigenous trees and shrubs seldom triggers symptoms. Tree pollinating months vary throughout South Africa, starting in late July and peaking in September in the Western Cape. In Gauteng, the tree pollen season is a little longer, but pollen counts have not been measured in that area for more than two decades. Gauteng has a large man made forest of trees that has matured in the last twenty years and it is likely that the tree pollen season is now much longer in that province. The tree season measured from pollen counts in the mid 1990’s in Gauteng occurred from July to November. In Kwazulu Natal the pollen count records date from the same time, showing the peak tree pollinating months to be August to October. The Mpumalanga tree pollen season was last measured in 2009 and peak counts were seen from September to November. A tree pollinating calendar for South Africa is seen below.
The peak tree pollen season in South Africa measured from pollen counts
Willow tree-Salix babylonica
There are several species of Salix, or willow, in South Africa but it is interesting to note that Salix babylonica, or weeping willow, often found close to rivers, has male and female flowers on separate trees. Where there are mostly female trees, less pollen will be found in the air, as it is the pollen from the trees bearing the male flowers that releases the windborne pollen into the atmosphere. This may be the reason that willow pollen has been less commonly found from pollen counts in South Africa.
Pinus or pine trees have been planted throughout South Africa. Pine pollen is large and has two air sacs which make it buoyant. It is easily transported by wind and may travel some distance from its source, sometimes settling as a pale yellow deposit on cars and buildings. Although pine is not a major allergen, it produces large quantities of pollen and may trigger conjunctivitis in spring when the tree pollinates.
Many species of the Rhus tree are found throughout South Africa. The pollen has been seen from pollen sampling studies in the Cape, in low numbers. The flowers are insect pollinated but contact dermatitis to the sap or the leaves has been reported.
- Schinus terebinthifolius– Brazilian pepper tree
The Brazilian pepper tree, has been extensively planted in southern Africa. It is insect pollinated but may trigger allergic rhinitis, conjunctivitis, asthma and contact dermatitis from the leaves or sap of the tree. Male and female species are necessary for pollination.
- Smodingium argutum– African Poison oak
This small allergenic tree or shrub has been likened to American poison ivy as its sap may cause a livid rash with blisters and swelling accompanied by intense burning pain which may persist for weeks. Male and female species are necessary for pollination. The tree resembles Rhus.
Major tree species identified from pollen sampling in South African provinces
|Southwestern Cape||Cypress, oak, olive, plane pine|
|Gauteng||Ash, cypress, Celtis (white stinkwood) elm, pine, poplar, Rhus (karee)|
|Kwazulu Natal||Morus (mulberry)|
|Mpumalanga||Oak, plane, pine|
Palgrave KC. Trees of southern Africa. C. Struik.; 1977.