Wind pollinated trees and hay fever

 As winter draws to a close I always look forward to the first hazel catkins, that signal a change in the seasons ......... but then, when spring finally does arrive, I remember that I suffer from hay fever. The early-flowering trees are wind-pollinated, producing vast clouds of sneeze-inducing pollen. 

Wind pollination is a chancy business and once the pollen is released it's rapidly diluted in the air, so the chances of an individual pollen grain landing on a female flower stigma, leading to the formation of a seed, decreases exponentially with the distance between then. So the only way to improve the odds is for trees to release great quantities of pollen

Male catkins of hazel.

Tiny, female stigmas of hazel

Male flowers of ash, about to open

Ash flowers, fully expanded

Silver birch male catkins, a major contributor to hay fever

Silver bird male catkins

Elm flowers. Before Dutch elm disease arrived, the bare crowns of mature elm trees were covered in a purple haze of flowers, a magnificent sight, now just a memory.

Most wind-pollinated trees produce their flowers on bare twigs, unencumbered by foliage that might hinder pollen release, but beech is an exception. It may be that beech bud burst is delayed because its foliage is very sensitive to late frosts. 

Evergreen coniferous trees like Scots pine tend to produce their male, pollen producing cones on the tips of their branches, well clear of the foliage, where pollen is easily carried away by the wind.

Yew tree pollination

 February is the month when the tiny male cones of yew trees begin to shed their yellow pollen. These were photographed in Teesdale a couple of days ago. 

Yew trees are dioecious - either male of female - and the male pollen is carried on the wind to single female ovules hidden amongst the foliage on another tree. These are tiny and can be hard to spot, but here is one, ready to receive pollen.

After fertilisation the outer wall of the ovule swells to become a soft, fleshy, aril that surrounds the single hard seed inside. It turns bright red in autumn, to attract the attention of birds. 

Every part of a yew tree, except the aril, is poisonous to humans but thrushes, fieldfares and redwings quickly devour them. Nuthatches extract the hard seed, wedge it into crevices in yew trunks and hammer it open to extract the kernel. There's more about them in this Guardian Country Diary.