The sex life of plants, including trees, is not simple.
Some, known as perfect flowered plants, have their male and female parts in the one flower so are effectively self pollinating (roses or apples); some, known as monoecious flowered plants have separate male and female flowers growing on the same plant (pine trees or corn) so do fertilise themselves but have to get their pollen from the male part of the plant to the female part : some, known as dioecious, are completely separate sexed with the male plant producing pollen and the female producing fruit.
Logically enough, the male dioecious plants are anxious to ‘put their pollen about’ as widely as possible so ensure that it is light enough to be carried by the lightest wind in the hopes that it will collide with as many female plants as possible. Meanwhile, female dioecious plants are anxious to capture as much pollen as they can on the pistils in the centre of their flowers. So they ensure that the tip of their pistils, the stigma, is broad and sticky and produces a negative electrical current. Airborne male pollen tumbling around in the air picks up a positive charge, and thus is drawn to the female’s sticky stigma and pistils.
So how do we come in? Well, as Tom explains, humans too emit a negative electrical current which means that if we come into contact with the positively charged pollen, our mucus membranes (eyes, skin, nose and throat) will trap it and it will often cause an allergic reaction. So the more pollen there is about, the more we are likely to suffer from pollen-related allergies.
But, surely this has always been the case? Plants have not suddenly changed the way they operate so why would we humans suddenly have become so much more sensitive to pollen? No indeed, plants have not changed the way they operate – but over the last 50 years or so we have.
In the early years of horticulture most plants, especially landscape plants and trees, were propogated by seeds and ended up as roughly 50-50 male and female, which meant that most of the male pollen got ‘captured’ by female plants. Enter the town planner….
Male plants, especially trees, produce no seeds, seedpods or fruits to fall all over the pavements and make a mess – but female trees do. As Tom describes in his new book, The Allergy Fighting Garden, the town planners’ desire to have clean streets persuaded them, whenever a tree needed to be planted, to plant a male tree. And their drive for clean streets was given a massive boost in the 1960s and ’70s when Dutch Elm Disease killed thousands of urban trees, giving the planners the chance to replace them with nice ‘tidy’ male trees which would not drop fruit over the pavements. What they failed to log was that all these male trees would, of course, emit massive clouds of allergenic pollen. Moreover, as the trees grow to maturity and get bigger, so the amount of pollen they release increases!
Tom has spent the last 30 years campaigning on this issue and gradually, the message is getting through, albeit slowly… Meanwhile, his campaign has been accompanied by a 30 year-long research programme into plants and their potential allergenicity – not just in a town planning context but for other communal environments and for individual gardens. As he points out, reducing the allergenic potential of one’s immediate environment (one’s own garden) can hugely decrease the overall allergen load and increase the allergy sufferer’s ability to survive in a high allergen urban environment.
The result is OPALS (the Ogren Plant Allergy Scale). Over three thousand plants, described, listed and ranked on a scale of 1 to 10 for their allergenicity. All appear in The Allergy Fighting Garden (many of them illustrated) along with much more fascinating information on the allergenicity of different plants and excellent advice on planting low allergen gardens and reducing one’s allergen exposure.
And don’t let anyone tell you that low allergen gardens are boring! There are masses of wonderfully interesting plants – like thisAlstroemeria, or the Iochroma Cyaneum above – that are way down on the OPALS scale but will still fill your garden with colour.
A recent report in the Lancet suggested that heart attack death rise by 5%, heart disease deaths by 6%, COPD (lung disease) deaths by 15% and pneumonia deaths by 17% on days with peak pollen counts. The link between pollen induced hay fever and the growing epidemic of asthma is strong; the cost to the health service and the economy in terms of drugs, doctor’s visits, lost work and school days is in the billions. And the misery – the streaming eyes, the stuffed up or running noses, the sore throats, the headaches and the antihistamine hangover – suffered by those with pollen allergies is just massive. Yet, there are so many ways in which to reverse the pollen scourge – we just have to do it!
So, if you suffer from hay fever, or you know anyone who does, or if your child does and there is a large pollen-emitting tree in the school playground, or if you have any influence on your local town planners – GO BUY The Allergy Fighting Garden (it is available via his website here or via Amazon in the UK) – read – and disseminate Tom’s ideas!
It is not that we have anything against male trees – but we want them out of our streets!!!
(The magnificent Rubrum Bowhall, by the way, at the top of the page, is a female Maple tree and has an OPALS rating of 1 – no pollen at all! And who would not want that in their garden, their playground or their street?)