• IT was encouraging to read the April 20 letter from Dee Searle about tree planting as one proposal to improve our air quality (Measures can be taken to improve air quality), but please may I add that birch trees are to be avoided.

Their bark is attractive but they are among the worst of allergen-producing trees. A warm spell in early April has made their pollen particularly heavy and I struggled to breathe when their pollen was at its most potent.

I was confined inside for two weeks and badly affected for much longer. The tree pollen season lasts from late February to early March to mid-June and the worst allergen producing trees, like birch, alder and hazel, all flower and produce pollen during this period.

Surprisingly the blossom of cherry and similar fruit trees is much heavier and stickier and less of a problem.

Birch pollen is the most common allergy after grass and affects 25 per cent of people who also have hay fever. Moreover, people with birch pollen allergy often develop an allergy to certain foods such as apples, peaches, pears, plums, nectarines, apricots, celery, cherries and nuts.

There are many plantings of young birch in Camden, some close to schools and nurseries and I noticed that Belsize Road is planted on either side with birch. These trees are there already but it would help to consider the allergen impact of trees when new plantings are considered.

Apparently the broad leaved trees are much more effective than the small leaf of the birch in helping to clean our air, and the very best trees for our environment are females from species with separate male and female plants as they bear no pollen and are allergen-free.

NAME AND ADDRESS SUPPLIED, NW1