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.

A year in the life of a beech tree Fagus sylvatica

Beech Fagus sylvatica autumn foliage almost glows when it changes colour in October.

Truly one of the finest displays of autumn, beech foliage almost glows on bright afternoons.

Beech nuts ('mast') and their husks. In occasional mast years a massive crop can be produced .....

.... which is good news for bramblings, that feed on the nuts.

The smooth, grey bark of beech trees often proves tempting for lovers who carve their initials in it. Wounds like this let in fungal infections that can ultimately kill the tree.

Young beech trees and clipped beech hedges retain their dead autumn foliage until spring.

A beech in the prime of life, at the beginning of winter.

Frost is needed to release the buds from winter dormancy ...

But unusually late frosts in spring can destroy tender young foliage.The fine hairs around the edge of the leaf tenfd to fall off after the pleats unfold and the leaf expands.

Beech male flowers

Coming into full leaf - the same tree as shown above in winter

Mature beechs have a massive root plate which sometimes give the appearance of the tree having melted into the ground.

Southern bracket Ganoderma autrale - often a killer of beeches. Here it's growing on an old stump ....

.. but more usually it grows higher up, weakening the trunk which can often snap in autumn gales, 10-12 feet above ground level. The fungal brackets are perennial, producing a new layer of spore tissue every year and generating millions of spores over the course of a several years.

More tree silhouettes in winter

Graceful silver birches Betula pendula

Sweet chestnut Castanea sativa

Hawthorn Crataegus monogyna. A tough, impenetrable tangle of branches, often with a twisted, fluted trunk when it is given time and space to grow into a tree.

Common lime Tilia europaea. Often has burrs at the roots with a mass of twigs, which have been trimmed in this specimen.

The mass of twigs growing from the burrs at the base of an untrimmed common lime

Beech Fagus sylvatica. Slender twigs with pointed buds.

Elder Sambucus nigra usually grows as a large hedgerow shrub that'sseverely cut back annually and only has a short life span but if it's left alone and given space it will grow into a small, densely-branched tree like this. Old elders have deeply fissured corky bark and twigs covered in yellow Xanthoria parietina lichen.

For more on winter tree silhouettes click here

The amazing hidden world of tree root systems

Some fine examples of tree root systems - and (scroll down) the micro-habitat they sometimes create:



An old oak tree rooted in a rock face at Plankey Mill in Northumberland.

Sycamore, beside the river Tees at The Meeting of the Waters in Teesdale, where winter floods scoured the soil away, exposing the roots ...

.... so that a lot of tree seems to be balanced on quite a small root system!

Young beech roots at Allen Banks in Northumberland, again exposed by water erosion. Interestingly, you can see how the roots autograft on to each other when they come into direct contact. In a few decades it might look like this....




.......a wonderful mature beech near Wolsingham in Weardale, where the mass of autografted roots seem almost to have melted into the ground.

The hollows formed where roots have grafted onto one another often house small pools of water, known as phytotelmata, which are home to transient communities of small organisms. These mini-ponds, trapped in a cavity formed by the coalesced roots, can contain vast numbers of small organisms, feeding in bacteria and fungi growing on the rotting leaves trapped in the water. The pool is fed by rivulets of water that trickle down the trunk when it rains. Temporary pools of water trapped in plants like this are known as phytotelmata. The pools in this beech tree's roots hosted nothing larger than rat-tailed maggots - the larval stages of drone flies. But while the species diversity in the beech-tree pool might have been low, the sheer abundance of the tiny single-celled protists that are present can be staggering ..............

These little organisms, taken from one of these beech root pools, are called Colpidium colpoda.  They're single-cell protists that swim with incredible speed using ciliary hairs on their surface, that beat in rhythm. Here they're magnified one hundred times. This single drop of  water on a microscope slide probably contained about five hundred...

Here they are magnified two hundred times. The circles that you can see in some of them are contractile vacuoles that constantly expel water from the cell cytoplasm.

At 400 times magnification you can see the fine cilia (top right) that are arranged in rows over the surface of the cell - you can just make out their dark parallel lines and you can also see algae that the Paramecium has ingested, inside the cell.

Static images don't really do justice to the helter-skelter movement of these little protists, so click here and click here to take a look at these two video clips of this sample, which give a much better impression of what is going on in those little temporary pools of water that you find trapped in beech tree root systems.

Fog and Fungi

A while back I posted about threats to the future of the Bishop of Durham's deer park at Auckland Park, in Bishop Auckland in County Durham. Thankfully these seem to have abated, much to the relief of all those who love the place. It's one of our favourite Sunday morning walks - even in the fog.

The park is at its best in autumn ....

.... especially when fog adds a touch of liquid magic to the spiders' webs.

I think it was Oliver Rackham, the noted tree and woodland expert, who once remarked that the only thing more useful to wildlife than a live tree was a dead tree. He was referring to the vast range of organisms - invertebrates, fungi, etc. - that live in or on the dead wood during a tree's protracted afterlife. Whoever manages the park at Bishop Auckland leaves plenty of dead wood for the benefit of organisms that thrive on it - like these tiers of bracket fungi (Ganoderma sp. I think) in the hollow trunk of this dead beech.

Some of the living beeches are under attack by honey fungus and their days are numbered - but there are also plenty of healthy trees and some replanting.

The stumps of old sweet chestnuts host these developing puffballs.

Sycamore, with the black spots of Rhytisma acerinum on the leaf blade.

Some of the living trees have magnificent rings of toadstools around their bases - I guess that these are a mycorrhizal species, that exist in a mutually beneficial association with the trees.

Not sure what these are, on a decaying beech stump. During the prolonged afterlife of the dead trees a whole succession of toadstools appear, some for just a few days.