From Bill & Laurel Cooper's book A Spell in Wild France. They are retired Brits who spent a few years on their boat at Aigues-Mortes which is on the Canal du Rhone a Sete (links the terminus of the Canal du Midi at Sete to the Rhone river at Beaucaire, just downriver from Avignon):

"Market day Mistral under the ramparts of Aigues-Mortes" For there is more to it than wind, at this time of year. The plane trees that would bring a welcome shade to the market in the sweltering days of July were showering down little feathered seeds. These lay in drifts a foot deep in every windshadow, and every gust of wind brought down more seeds to mix with those stirred up from the drifts. The seeds clung to everything. They penetrated the hearts of lettuce, the scales of glove artichokes, they settled in neat rows, between the clumps of asparagus.

For these seeds are one of the great plagues of Aigues-Mortes. Even to the resolutely unallergic came a dripping nose and stinging eyes. As the great plane trees, so beloved and cool in summer, now sifting the spring sunlight through a tracery of buds and young green leaves, shook with every gust of wind another million seeds came whirling down, on to cafe tables, the stacked plates, the folded napkins. We placed beermats over our drinks and stayed under the awning of the Express, and watched tourists shuffle ankle deep through the fluff, watched the brims of their hats fill up, watched them peering down their camcorders while their pint of beer collected a froth that had nothing to do with brewing. Even into your oysters, your champagne bucket, and your panache de poissons sauce oseille, came drifting down Aigues-Mortes special April garnish: a sprinkle of fluffy plane sees."

I love plane trees but mostly because I associate them with gracious avenues and boulevardes of well-designed cities, mostly in France, especially Paris where I lived for years. But also Asian cities that benefited from French town planning (notably Hanoi and a few Chinese ones, I think Nanning is famous for their shaded avenues). I don't know if Australian natives can really substitute. What does Buenos Aires use?

Anyway I think the annual "snow" and leaf shedding is inseparable. In France it is a part of the changing of the seasons. At certain times of the year (towards the end of winter I think?) there are big teams of men pruning the trees. Parisian streets are swept regularly anyway so I am not sure the leaf or blossom fall is an especial problem.

@ Michael James

"I don't know if Australian natives can really substitute."

For a start this is Australia, not Hanoi or Paris.

If you fail to appreciate the splendour of a flowering gum, its roughly doomed canopy coated in either snowy white or blood red blooms, a stately straight salmon coloured trunk, large glossy deep green leaves in favour of the pallid plane tree, then that is your choice.

I knew an immunologist would stomp all over me. (I'm a molecular-geneticist/biochemist but several decades since I gave up trying to follow the utterly arcane details of immunology).

The thing is some people do grow out of their allergies. In my case I am persuaded it happened only because I suppressed reaction each year with those nasal corticosteroids. Unless the original antigen-stimulated cells disappear then it is hard to explain how the whole thing just disappears, especially if antigen-exposure of the cells is still happening each year; for me there was a 20 year break between over-exposure to the jasmine so that is a special case and understandable. But whatever happened in Paris was happening while still being regularly exposed to whatever it was (the endocrinologist did those scratch tests and probably told me the culprits but I don't remember exactly; it was several things including grass spores)

And my reaction was getting pretty bad to force me to a doctor about it. At times I had to lie down at work for a few hours to allow anti-histamines to begin to work (you know how it is, if the reaction starts before taking the meds it is hard to stop; one often hesitates taking the meds because they pretty much knock you out from doing useful work anyway; my other strategy was to spend time in a 4 degree coldroom!)

Michael James - one of the keys to understanding clinical immunology is to also understand the other clinical sciences - anatomy, pathology, physiology, pharmacology - because they are all linked.

Rather than inventing new theories, it might be useful to see whether your dilemma has already been answered - why do some people "grow out of their allergies"?

There are many examples of this. Classically, children almost always outgrow egg allergy. Asthma is much more common in childhood (also a type 1 hypersensitivity if it is the allergic type). There is good evidence that IgE-mediated Type 1 hypersensitivity diminishes with age. There is associated evidence that IgE production diminishes with age. Here is a good review:
http://www.immunityageing.com/content/2/1/9

I am always puzzled when people stick to their own theories despite the evidence. Michael - don't you find it frustrating if people expound their own theories in your own areas of expertise?

Sue, perhaps my tone was poorly judged or executed but I was not entirely serious. On the other hand, while in fact I did say that my ageing during the period of my loss of my allergies was probably a factor, the dramatic loss over just a few years--while the environment remained as allergenically hostile as ever--and that it perfectly coincided with the use of the nasal spray, indicated to me that the strategic use of the corticoid steroids was pivotal.

Oh, and ok I must admit to a certain robust scepticism of immunological explanations and theories. I have been hearing wildly optimistic predictions of a malaria vaccine for at least 3 decades (even, embarassingly in the Australian fashion, prediction of an Australian Nobel prize for such). It is not that I am unaware of the huge problems but it is the ridiculous confidence and the almost magical solutions that irritate me. (In my own area the absurd hype about genomics solving diabetes every other year is the equivalent, however I am only one amongst many who cringe everytime one of us gets in front of a camera spruiking such stuff--last week it was Encode; talk about deja vu, these guys should and do know better.)

So you see (to dig my grave a bit deeper) you have in fact not presented any satisfactory explanation for my outcome. Of course it is an experiment of one. But I note on this comments thread people still trying/failing to solve their recurrent problems with anti-histamines which I too did for years. They have improved (less drowsiness) but they are no solution and certainly never lead to a decrease in reaction to next year's pollen season. I wonder what the data is on appropriate use of the nasal spray (which is OTC in France but only prescription last time I checked in Oz; not that I would for a moment suggest this is some conspiracy to sell expensive but ineffective drugs for ever.)

Michael - you seem to be confusing the products of immunological therapy (vaccination) with an understanding of the mechanisms of clinical immunology.

Anti-histamines and steroids act on the inflammatory mediators, once released. In a sense, they represent symptomatic treatment.

You might want to read about desensitisation or immunotherapy , which has been found to be both more effective and more cost-effective than either steroids or anti-histamines.

Sue

I am one of those for whom the desensitising program did not work. After the skin tests had been examined, the doctor concluded I was allergic to the usual suspects like pollen but not to other substances like chemicals. I had red swellings on the "pollen" arm and none on the "chemical and other stuff" arm.

10 minutes later I was waiting for a tram and both my arms swelled into sausage balloons, it was also one of those windy spring days. I went back to the doctor - he stated that this was not a problem, because I did not react within the time period given to the irritant test!

I was on only my third desensitising treatment, when I had an anaphylaxis response and had to be rushed to hospital for a shot of adrenalin.

I stick to using a preventative inhalant these days, as I swiftly become immune to tablet forms of anti-histamines.

And I think you know where the medical profession can shove their desensitising programs.