Alder leaf beetles

 Low Barns is Durham Wildlife Trust’s largest wetland reserve and the commonest trees there are alders, whose leaves are currently being consumed by a population explosion of these jewel-like, metallic-blue alder leaf beetles Agelastica alni.

Until quite recently, the alder leaf beetle was considered to be a rare species, in danger of extinction in Britain. Then, in 2004 it reappeared in north-west England and over the last twenty years it has become increasingly common in the north east. No one has really identified the reason for its success but it’s common in France, so perhaps it arrived with imported plants from continental Europe. The adult beetle and its larva partially defoliate alders but they recover every spring. The adult beetles fall with the alder foliage in autumn and survive winter in the leaf litter.

Goldfinches, alders and dandelions

 

It's hard to over-estimate how important alder seeds are as food for small finches in winter. Siskins love them, but so do goldfinches, like these that I watched on a walk near my home yesterday. 

Goldfinches are also fond of dandelion seeds and, although the main season for these had long passed, there are always late-flowering dandelions around. This goldfinch was feeding on dandelion and lawn daisy seeds on a grassy verge at the beginning of December.

New Year Plant Hunt in and around Durham city today

A second day of New Year Plant Hunting, this time along the banks of the river Wear and along woodland edges and hedges. Nineteen species in flower this time, of which these are some of the most pleasing:

Alder catkins

Hazel catkins

Hogweed

Nipplewort Lapsana communis

Lesser celandine, flower petals eaten by a slug but very attractive variegated foliage.

...... and cowslip, flowering four months early.

The cowslip was on the Durham University estate, on the Mountjoy site, about 400 metres from an area that was seeded with wild cowslips about 20 years ago. Since then they save seeded themselves on various places, most likely with seed carried on feet of staff and students. This single flowering plant was amongst a population of over 50 non-bloomers, all with very vigorous new leaf growth, on a very sheltered grassy bank under an alder.

Alder's Hidden Charms

There isn't a lot of colour in the countryside at the moment but this brightly coloured alder timber, in a small local wood where the owner had been pruning and thinning trees, livened up a dull, grey day. Common alder is a somewhat sombre tree, so it always comes as a surprise the see the bright orange pigmentation that develops in the newly-cut wood. It looks like this particular tree was about thirty years old.

When you look a little close the colour becomes even more striking because the inner layers of bark have a distinct violet hue, similar to the colour of the tree's bud scales when they begin to swell in spring.

Alder timber isn't of much use when dry, other than for making charcoal that was particularly valued for the production of gunpowder. It's a different story, though, if the wood is kept permanently wet because then it is long-lasting. It was the favourite material for making soles of clogs, both because of its toughness when wet and because of its resistance to splitting when small nails are driven in around the edge of the wooden sole. It also made excellent piles for driving into the ground for bridge foundations.

A Tree-Spotter's Guide to Flowers: 2

Many trees produce their flowers in elongated catkins in spring, often before the foliage expands. Most - but not all - catkin-bearing trees are wind pollinated and produce vast quantities of pollen to ensure that pollination and seed set occurs. Hazel catkins are the most familiar ....

... along with alder catkins. Alder is usually the first tree to flower in spring.

Male catkins of hornbean are smaller than those of most other trees and produced just before the leaf buds open.

Silver birch male catkins are long and slender. The female catkin, seen here just above the leaves, is much smaller and points upwards. It will produce large quantities of seeds in winter, which are important food for finches.

Silver birch tree in full flower, in April.

There are separate male and female trees of goat willow (also known as sallow). This is the female catkin, with large numbers of stigmas. After pollination it'll produce masses of downy seed in early summer. Unlike all the other trees in this post, goat willow is pollinated by insects - flies, bees and butterflies - and both male and female trees are sometimes visited by blue tits that also have a liking for nectar - so this may be the only tree species in Britain that's pollinated by birds.

Male goat willow catkins, beginning to expand their golden stamens.

A male goat willow tree in full flower in late March can light up a hedgerow - and is an important source of nectar and pollen for the first insects that emerge in spring.

Poplar catkins are seldom seen (unless you go tree-spotting with binoculars) because they are produced right at the top of mature trees, but they are often the most attractive flowers of all the wind-pollinated species. They are much stouter that catkins of other trees. The best time to look for them is after a spring gale, when they are often broken off and litter the ground under the tree.

For more information about trees click here

A Tree-Spotter's Guide to Bark: Part 2

The grey-brown bark of alder Alnus glutinosa isn't particular distinctive - unlike the wood within. Freshly-felled alder wood turns a startling shade of red, although this quickly oxidises to a pinkish-brown. Understandably, the blood-like shade of the cut timber gave rise to many superstitions but didn't stop the coppicing of the tree for the production of high quality charcoal for gunpowder. Alder wood lasts exceptionally well if it's kept permanently wet or submerged - not surprising really, considering the tree's propensity for growing on riverbanks that frequently flood - and it was sometimes used for piles in bridge construction and also for the soles of clogs.

Wild cherry or gean Prunus avium bark is easily recognised by the long horizontal scars (lenticels) that run across the trunk. These are areas of porous bark that allow gas exchange for the living tissues below that generate new wood each year. Cherry bark also has a tendency to peel away in narrow strips around the circumference of the tree.

From a distance silver birch Betula pendula bark is dazzling white when it catches the sunlight, but a closer look reveals subtle shades of pink, orange and brown showing through from the bark tissues just below the surface. At this stage in the tree's life the birch bark peels away, sometimes in large sheets, as the diameter of the trunk expands (and so is ideal for birch-bark canoes) but as the tree ages....

-- the bark splits vertically, separating the white bark into flakey patches between deep fissures.

For more information on tree identification click here

A Tree-Spotter's Guide to Fruits and Seeds: Part 5

This little huddle of 7-spot ladybirds, apparently settling down for communal hibernation, were a bit premature in their choice of these unripe alder Alnus glutinosa cones as a resting place last week. Within a few days the cones will begin to ripen ....

... become woody and spit open. You can just see the tiny chestnut-brown seeds inside. They are an important food source for many birds in winter and are released in vast numbers from now until January. The tree will be flowering again in February and you can see next year's embryonic cones already formed - they are the little knobbly things on stalks, top left, next to the bud at the tip of the shoot. Above the ripening cones you can also see next spring's male catkins already forming.

Alder cones tend to stay attached to the tree for a long time - these old ones would have shed their seeds back in October-November 2009.

Ever since grey squirrels moved into my part of Durham it has become harder to find fully ripe hazel Corylus avellana nuts - the squirrels take them while they are still at this green stage. Filberts are cultivated hazels that have much longer leafy bracts sheathing the nuts.

Wild cherry or gean Prunus avium fruit ripens in July. A couple of years ago I did a taste test on as many different fruit-bearing wild cherry trees as I could find. They were surprisingly variable - most were breathtakingly sour but a few were sweet enough to eat. The hard seed inside the fruit is a favourite food of hawfinches - one of the few birds with a beak that's powerful enough to crack it open. Everytime I see a tree in fruit I scan the ground below for a hawfinch eating the seeds from rotting fruits: no luck so far but I live in hope...... The hard cherry stones are also popular with field mice. When I demolished our old garden shed I found a mouse's stash of scores of cherry stones from the tree that used to grow in our garden hedge, each with a neat hollow nibbled in it.

Professional foresters can identify conifers just by crushing their needles and sniffing their resinous aroma. This is one of the easier ones for scratch-and-sniff botany - Western Hemlock Tsuga heterophylla (which is not related to the hemlock that poisoned Socorates). Apart from the hint of citrus scent in its resin (some say it smells like ground elder), it bears these small purplis cones and the shoots carry needles of varying lengths. It's a native of the west coast of North America, but often seen in forestry plantations in Britain, especially on the wetter western side.

For more posts on tree ID click here

Trees Under Attack

By this time of year many trees are showing signs of fungal attack. This strange growth on a developing alder cone is caused by a gall-forming fungus called Taphrina alni and is commonly known as alder tongue gall. An uninfected cone is illustrated below, for comparison. When the gall is mature it resembles a crimson tongue and occasionally you find several protruding from a single cone. Taphrina alni first arrived in Britain from France in the 1940s but didn't reach North East England, where it's becomong increasingly common, until the 1990s.

Turn over an aspen leaf like the one above and you may find its underside covered with clusters of golden spores, belonging to aspen rust fungus Melampsora larici-tremulae. Rust fungi have complicated life cycles, infecting different hosts at different times of the year.

When these leaves blacken, wither and fall to the ground they'll release spores that will infect next spring's new growth of larch needles, and the spores that form on those will then reinfect aspen foliage. This leaf came from an aspen growing near a larch plantation.

Aspen, whose leaf stalks are flattened along their sides, so that they flutter sideways in the wind and seem to tremble in the slightest breeze, normally turn an intense shade of lemon yellow in autumn, but the rust infected leaves simply wither and fall without changing colour.

A Tree-spotter's Guide to Buds: part 2

White poplar Populus alba winter buds are covered in a dense felt of fine white hairs that, from a distance, make the twig look as though it's been dipped in white emulsion. The white hairs cover the underside of the leaves too, which flash green and white when they flutter in the breeze in spring and yellow and white when they change colour in autumn.

Alder Alnus glutinosa buds have this beautiful violet-purple sheen that intensies in spring, as the buds begin to swell

Common lime Tilia x europaea buds, which are rounded and have few bud scales, develop a deep crimson hue when they're exposed to sunlight, but on their shaded underside (right hand twig above) they remain green. The purple pigment is produced in response to bright sunlight.

Sweet chestnut Castanea sativa buds are also tinged red but the twigs are chestnut brown. Notice how the buds below the terminal bud sit on a little shelf.

... and this is rowan Sorbus aucuparia, possibly the least attractive buds amongst native species, whose hairy, pointed buds lack shiny scales.

For part 3 see http://cabinetofcuriosities-greenfingers.blogspot.com/2009/12/tree-spotters-guide-to-buds-part-3.html

For part 1 see http://cabinetofcuriosities-greenfingers.blogspot.com/2009/11/tree-spotters-guide-to-buds-part-1.html

For more posts on tree ID click here