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Pests, diseases, disorders, competing growth and unfavourable conditions (a field trip): the pests and disorders
Posted on February 11, 2010 by Ash
On Thursday the 21st of January my arboriculture class set out from college on a field trip to see a smörgåsbord of pests, diseases, disorders, competing growths and unfavourable conditions afflicting a variety of trees in the vicinity of York and Malton. Some of them were new to me, most I was already aware of, but it made for a very interesting way to spend a day and we got to see some cracking trees. Here’s a quick run-through of the pests and disorders that we saw:
Rabbit damage at base of ash (Fraxinus excelsior).
European rabbit (Oryctolagus cuniculus) - The field trip took place in a particularly harsh winter and the poor old bunny rabbits had resorted to stripping bark from trees. The damaged trees we saw formed part of a rough hedge along a field and were growing right beside a few rabbit burrows. The photo shows damage to an ash but we also saw damage to a tiny hawthorn (Crataegus). Bark stripping weakens trees (when trees are ring-barked / girdled all material above that point dies) and opens them to infection. [Other animals such as hares, deer and squirrels will also strip bark.]
Graffiti carved onto a beech tree (Fagus sylvatica).
Humans (Homo sapiens) – The example we saw was disfiguration of the bark by people carving initials or symbols. Graffiti has a negative impact on the aesthetic appeal of the tree and can open it up to infection. [Other examples of direct human damage: vandalism (breaking off branches), vehicle damage (usually inflicted by tall vans and lorries), and butchery by D.I.Y. / cowboy tree surgeons.]
Witch’s brooms on downy birch.
Witch’s broom (Taphrina betulina) – T. betulina is a fungus that causes dense balls of twigs (that look like birds nests from a distance in winter) – witch’s brooms - to form on the branches of silver and downy birches (Betula pendula and Betula pubescens respectively). As far as I was aware* the fungus doesn’t have any significant effect on the health of host tree, although as witch’s brooms grow larger every year, I assume that they eventually become so heavy that the supporting branch will break.
Included bark (to the left of the red line) in the crotch where two main stems meet on a beech.
Included bark - “Included bark forms when the bark of the branch and trunk squeeze together” (Shigo, 1991) 2. “In crotches that have very narrow angles of attachment the branch bark ridge [a ridge of bark in the crotch] sometimes fails to expand outward and is swallowed by the growth of the branch and trunk. Each year thereafter, more bark is enclosed within the crotch. This condition is referred to as included bark… Included bark has long been associated with weakness in tree crotches since it is frequently seen in failed tree forks. It is easy to assume that the included bark prevents the formation of connecting wood between two stems and therefore reduces crotch strength. …branch attachments with included bark are inherently weak and should be removed” (Farrell, undated) 3.
Sphaeroblasts - Disappointingly, I don’t have a photo of these intriguing fellas. You ever seen a Malteser- to fist-sized ball in the bark of a tree? Those are sphaeroblasts, described by Strouts & Winter (2000) 4 as “Bark-coloured spheroid lumps, small or large… woody, bark-covered structures, being an abnormal development of a bud which has produced annually a woody sheath without ever producing a shoot. Harmless.”
A large burr on an English oak (Quercus robur).
Burrs or burls - The burr we visited on our field trip – seen in the photo above – was a huge burr on a good-sized oak. It formed in a similar way to how sphaeroblasts form – the difference I think is that the buds in a burr are on the outside of the bark, not beneath it. The buds seem to multiply like crazy and sometimes produce tiny little shoots that never amount to anything. As far as I know, burrs are harmless to trees. They’re supposed to be highly valued by craftsmen because of the spectacular grain of the wood inside.
A pair of oak marble galls (one not fully developed) [photo taken 15 January 2009].
Galls - We saw a few old marble galls on the oak with the massive burr. I mentioned these in a post in January 2009: oak marble galls [are] caused by asexual Andricus kollari larvae. A. kollari is a member of the family Cynipidae, “whose members are of special interest because most of them induce gall formation on plants and many of them display a marked alteration between sexual and parthenogenetic generations. They are called gall wasps… Most of the European species occur on oaks, although some species attack roses and certain herbaceous plants. There are about 90 British species.” - from Chinery’s Insects of Britain & Northern Europe (Collins Field Guide, 1993). Again, as far as I’m aware, galls don’t significantly affect the health of a tree in normal conditions.
Posted on January 6, 2010 by Ash
A snowy scene in Lower Whitwell Wood, looking west across Whitwell Moor to distant Millstones Wood.
It’s been snowing a lot lately. In fact, the last couple of weeks have made 2009/2010 the snowiest winter in these parts since 1981/1982. I went for a walk on Saturday afternoon when there was still plenty of snow around up on the tops. It snowed a lot Saturday evening, and I went for another walk Sunday afternoon on which I took these photos. Then yesterday the weather went beserk and it put down, on average, nine inches of snow around the house. And more snow is forecast! It’s brilliant!
A pair of reasonably lonely oaks not far from an even lonelier one.
This bleak and snowy scene may not have much in the way of trees, but I’ve included it here as it’s the view to the south-east from…
…the Lonely Oak. (There are now eleven different photos of the Lonely Oak on treeblog’s Flickr.)
There were a fair few tracks around the Lonely One. The two tracks in the bottom left part of the photo were made by one or more rabbits or hares, (likeliest to be rabbit, I’d say). From the book Animal Tracks and Signs by Bang and Dahlstøm (2001): Each of the regular print groups is made up of four separate footprints, at the back the two short fore prints, one behind the other almost in a line, and at the front the two hind prints, more side by side and usually longer than the fore prints. So the furthest-left track was made by a rabbit/hare heading towards the camera; the track to the right of it was made by a rabbit/hare heading away from the camera. The track with the funny lines coming out of the bottom right corner is probably from a little dog; the lines would have been made by paws skimming the top of the snow.
There were tiny icicles dangling from the Lonely Oak (an English oak, Quercus robur). Is that a gall I spy in the background?
The Trig Point atop the western Salter Hill.
A lovely pair of Scots pines (Pinus sylvestris). They appeared in a couple of posts last March when summer was near and snow wasn’t on my mind.
This would be the view from the top o’ the hill, looking south-west towards the darkly wooded upper Ewden Valley and Pike Lowe (on the horizon, slightly right of centre). Snowtastic.
A snowy cluster of mushrooms. This photo was taken on my Saturday walk, but I’ll sneak it in here. I love those gills.
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Posted on July 20, 2009 by Ash
I went out on the moors on Saturday with the intention of making Pike Lowe, and, if I had the time, of finding the mythical waterfall far up the Ewden Beck...
First checkpoint: the Lonely Oak of Whitwell Moor.
It doesn’t appear to be doing too well, our Lonely one. Most of its leaves are crinkled and ragged-looking, whereas the rest of the oaks I saw on my ramble were all healthy. So it’s not a weather thing. I couldn’t find a single developing acorn on any of the oaks, which is disappointing as I was thinking of planting some for treeblog Set D. The red balls on the leaf in the photo are galls.
A Jew’s ear (Auricularia auricular-judae) –like fungus growing on a dead branch attached to a living English oak (Quercus robur) in Millstones Wood.
Also in Millstones Wood, a beast of a beech (Fagus sylvatica). This looks like an old coppice to me. There may not be any acorns this year, but there’s no shortage of beechnuts: the floor was covered with cupules!
Leaving the wood behind, I was confronted with a field full of near fully grown cattle. I had to pass within a metre of these two, but they seemed completely indifferent to my presence. I was glad to avoid a trampling! Broomhead Hall Farm can be seen across the valley in the background.
Developing hawthorn (Crataegus monogyna) fruit, or haws. The hawthorns hereabouts were in full flower at the end of May / beginning of June.
Looking back across the moors to Millstones Wood from near the summit of Pike Lowe, just over an hours walk away!
The cairn on the summit of Pike Lowe (OS grid. ref. SK 208 974 or 53.4726° N, 1.6865° W), 476 metres above sea level. So close to civilisation, yet so isolated.
Posted on May 26, 2009 by Ash
Sunday was a real stunner, and after the dire weather of May so far it was even nicer than usual to get out into the countryside. I took the pushbike for a ride over to Langsett, going clockwise around the reservoir via North America before coming through Upper Midhope and heading for home.
Clusters of male catkins dangling from an English oak. The English or pedunculate oak is a monoecious species so individuals produce flowers of both sexes.
This particular oak had pea-sized galls attached to some of the catkins. I’m fairly sure that they are the sexual galls, known as currant galls, of the currant gall wasp (Neuroterus quercusbaccarum). Common spangle galls found on the underside of oak leaves are the agamic galls of the same wasp.
An old friend: the rowan on Whitwell Moor from under which I collected half of my berries for Set C (replanted as Set C(r) a fortnight ago). Rowans are in full bloom at the moment, and this one was no exception. It was absolutely covered with infloresences!
A bit of lovely lichen growing on the rowan.
Get a close-up look at one of the inflorescences.
This young ash grows on the aptly named Long Lane and I’ve developed a habit of taking its picture every time I pass by, which allows for some interesting seasonal juxtapositions. Here it can be seen in the thick of a blizzard on the 2nd of February and also just coming into leaf in happier weather on Sunday. (See the same ash with and without leaves last October and November respectively in this post!)
The other rowan whose seeds comprise Set C(r). This unique and arresting rowan unfortunately blew over last year. It was still lying where it had fallen on the wall the last time I visited on the 14th of February, but since then it has been cleared away.
The only extant trace is this stump. The fallen tree was still alive too – I noticed live buds during my February visit. It must still have been connected to the root system. I hope that the roots continue to live and send up new sprouts, but given the stump’s situation in a field oft home to a herd of cattle it may never be able to re-establish anyway. I really hope that the seeds I took from it last year germinate to allow me the pleasure of raising the offspring of a remarkable ex-tree.
I took this photo looking south up-valley while standing on the bridge over Thickwoods Brook where that stream enters Langsett Reservoir. The brook gathers in the wee pond you can see in the bottom right of the photograph before rushing down a little weir into the reservoir.
Still on the bridge, but looking east towards Thickwoods, a coniferous plantation owned (as is the reservoir and much of the surrounding land) by Yorkshire Water. See what I mean about the bilberry being vivid? It’s almost glowing!
Posted on January 16, 2009 by Ash
What is a gall? The British Plant Gall Society’s site has a good definition from Redfern & Shirley’s British Plant Galls:
A gall is an abnormal growth produced by a plant or other host under the influence of another organism. It involves enlargement and/or proliferation of host cells, and provides both shelter and food or nutrients for the invading organism.
British oaks are particularly rich in galls. Here is just a tiny sample.
A pair of oak marble galls (one not fully developed) caused by asexual Andricus kollari larvae. A. kollari is a member of the family Cynipidae, “whose members are of special interest because most of them induce gall formation on plants and many of them display a marked alteration between sexual and parthenogenetic generations. They are called gall wasps… Most of the European species occur on oaks, although some species attack roses and certain herbaceous plants. There are about 90 British species.” - from Chinery’s Insects of Britain & Northern Europe (Collins Field Guide, 1993). This page at hedgerowmobile.com details the life-cycle of A. kollari and has good photos of the wasps and larvae with cross-sections of the gall.
A pair of artichoke galls caused by asexual Andricus fecundator larvae. Another gall wasp, A. fecundator is closely related to A. kollari. I’ve known about marble galls since I was a kid, but my first encounter with an artichoke gall came recently, in September 2007, on a university field trip to Kintyre. How did I ever miss them? hedgerowmobile.com has an A. fecundator page too.
An unknown gall. Perhaps a partially formed marble gall?
An unknown bud gall. If you recognise this gall and can ID the causal agent, please leave a comment.
Enough galls; how about some fungi? This weirdness has taken over the underside of this branch. The top side is covered with leprose lichen.
More leprose lichen. Notice how it only grows on the right side of the branch. There must be a favourable microclimate there, perhaps because of sunlight or exposure.
Another lichen; this one is fruitcose. As for what species it is… I wish I could tell you.
The subjects of all those photographs were found on this one English or pedunculate oak (Quercus robur). Even though it has split in two, both halves continue to grow; in fact, the large branch that goes off to the right is impressively long.
One more thing! A reminder about the next edition of the Festival of the Trees, which treeblog will be hosting. Please submit your blog posts, photographs, poetry, works of art, articles, news pieces, bark rubbings and anything else tree-related to mail [at] treeblog [dot] co [dot] uk, making sure that Festival of the Trees or FOTT is contained in the subject header. Alternatively, you can use the online submission form at blogcarnival.com. You do not need to be the author or artist of the content you submit. Although there is no theme this month, it would make my day if you submit something pertaining to a particular favourite tree of yours! The deadline for submissions is the 30th of January, so that leaves you a fortnight to get them in. Get to it!
Posted on September 23, 2008 by Ash
An area of clearcut coniferous woodland in Alport dale. There were a few signs around explaining that over the next 40 years, most of the existing timber-producing conifers will be cut down and replaced with native woodland. So alders and rowans and birch and oak and hazel and the like. Sounds good!
Looking over the edge at Alport Castles. The famous Tower is just off-picture to the left. There’s quite a lot of coniferous forest in the background to replace!
Just off the moors the footpath heads through a nice bit of birch-rowan woodland.
Updated December 2008. Silk button spangle galls produced by the silk button spangle gall wasp (Neuroterus numismalis) on the underside of a fallen English oak (Quercus robur) leaf.
Looking downriver from the old packhorse bridge at Slippery Stones. The 17th century bridge was originally further downstream but while Ladybower Reservoir was being built in the first half of the 20th century, the bridge was taken down and the stones numbered, then reconstructed at its present location.
Around the corner from Slippery Stones, at the bottom of Cranberry Clough – this lonely downy birch (Betula pubescens).
Just below Upper Midhope now, and it’s almost sunset.
Just along the road from the preceding photo – and but a stone’s throw from the fallen rowan – I took a rest on this old gate.
P.S. It might be little late in the day, but if you haven’t already, go check out this month's Festival of the Trees (No. 27) over at Exploring the World of Trees.
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