Arboriculture & Urban Forestry 32(4): July 2006 135 after kissing a person who has eaten a kiwi fruit (Mancuso and Berdondini 2001). The symptoms most often induced by crossreacting food are oral symptoms such as itching of the lips, mouth, or pharynx and swelling of the lips, tongue, throat, and palate (known as the oral allergy syndrome [OAS]). Urticaria and more severe symptoms can, however, also occur (Ortolani et al. 1988). Birch pollen-related food may induce immediate or late eczematous reactions in children as well as in adults having atopic eczema (Reekers et al. 1999; Breuer et al. 2004). It seems that birch pollen can also give an intestinal inflammation. A significant increase of gastrointestinal symptoms was found in adults (with birch pollen allergy and a history of rhinitis) during the birch pollen season (Magnusson et al. 2003). DISCUSSION There is substantive evidence in the medical research litera- ture to show that tree pollen of certain species is a significant cause of hayfever and asthma. This is particularly so in urban environments. Although pollen from other tree species such as acacia (Pumhirun et al. 1997), Japanese cedar (Nakagawa et al. 1996), Arizona cypress (Charpin et al. 2005), and olive (Geller-Bernstein et al. 1994) also are known to cause asthma and hayfever, in this article, we are dealing with birch, which has been shown to be a major cause of pollen allergy in some countries. Furthermore, although patients with an allergy to pollen from oak, the beech family (Fagaceae), alder, and hornbeam have been found to have a monoallergy to these trees, they also always have birch allergy. There is substantive evidence in the medical research lit- erature to show that birch tree pollen is a significant cause of seasonal hayfever and asthma. This is particularly so in urban environments. Compared with other tree species in New Zealand, silver birch pollen is the major cause of hayfever and asthma. Another potential threat is the increase in the number of olive trees in New Zealand. However, olive groves are not planted in urban areas and therefore are not likely to become as great a problem as birch trees. Silver birch pollen is also linked to allergic reactions to some food. Measures suggested for avoidance of problems related to allergenic trees include avoiding planting new trees, espe- cially near human population centers, and agronomic re- search for hypoallergenic trees (Charpin et al. 2005). In Eu- rope, the silver birch is a native species and therefore it is not practical to consider removal of the trees. Avoidance of pol- len is difficult, but there are some measures that can be taken. For example, making use of pollen counts, staying indoors, and the use of protective sunglasses may help. Silver birch has commonly been used as a street tree in many cities, including New Zealand. This practice continues in major cities such as Auckland and Christchurch as well as in neighboring and recently established towns. For example, in Rolleston (a new and rapidly expanding town south of Christchurch), silver birch has been planted along the main streets. There is anecdotal evidence of increased numbers of patients with allergy symptoms being referred from the Rolleston area (Spellerberg, pers. obs.). In general, the extent of the birch pollen health problems, the medical costs, costs to individuals and their families seems not to have been calculated. Even if there were any doubts about the extent of the issue, the precautionary prin- ciple must surely apply. Planting tree species that contribute to health problems should be avoided. At the very least, the costs of removal of existing birch trees should be weighed against the medical costs and other costs incurred by allergy sufferers. In view of the findings of the research in the medical literature, there appears to be a growing health problem caused by birch pollen in urban environments or where groups of trees have been planted in locations where many people aggregate for work or other activities. With regard to birch trees on public land, we suggest that councils should consider the following: • Prepare an education program and promulgate the health issues; • Introduce a policy of not using silver birch as a street tree or amenity tree; and • In countries where silver birch is an introduced species, gradually remove existing silver birch trees from public places. Implications for Arboriculture Arboriculturalists should be aware of nuisance factors of trees and particularly those that cause health problems. This is particularly important for those trees used in city and urban environments. We believe that the human health problems caused by the pollen of silver birch are not well known among arboriculturalists or landscape architects in New Zea- land and possibly elsewhere. Glossary These definitions are taken from Johansson, S.G.&Bieber, et al. 2004. Revised nomenclature for allergy for global use: Report of the Nomenclature Review Committee of the World Allergy Organization, October 2003. Journal of Allergy and Clinical Immunology 113:832–836. Allergen: an antigen causing allergic disease. Allergy: a hypersensitivity reaction initiated by specific immunologic mechanisms. Atopic disease: disease of atopy, e.g., allergic asthma or rhinitis. Atopy: a personal and/or familial tendency, usually in childhood or adolescence, to become sensitized and pro- duce IgE antibodies in response to ordinary exposures to ©2006 International Society of Arboriculture
July 2006
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