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Summer in March: A walk on the moors

A couple of days ago I returned home from half a week on Mull & Iona, where I saw an enormous fossil tree… but that’s another post! The weather up there was for the most part dull and drizzly, and in Sheffield today it put down a few inches of late snow. Yet before I went away we had some incredible weather at home. It was like high summer, but in March…

Holt House, an abandoned farm on the other side of the Ewden valley, stands close to some quite old and fairly gnarly trees. In the foreground, Rhododendron ponticum is colonising the moorland – it has already claimed the valley side down to the river. It would be the mother of all nightmares to eradicate at this stage, and it gets worse every year.

Park Cote, the walled area, is on the same side of the valley as Holt House. With another abandoned building or two (they draw me in!), it’s been on my list of Places To Visit for a while now.

A typical Oaken Clough scene: a lovely, big, lichen-encrusted birch, plus rowan, more birch, bracken, moss, holly, heather, lichen-encrusted rocks, a wee burn… it’s paradise.


A rowan in its prime leans out over Ewden Beck high up the valley. The river was very low; much of the riverbed was exposed and dry. This section is bare bedrock.

A close-up of one of the exposed stumps you sometimes stumble upon out on the moors, usually in groughs: relics from a time long ago when the moor was not a moor but a wood. The peat preserves the timber really well.

A larch rose in the making! I love larch roses. They can’t fail to put a smile on your face.

Holt House again, surrounded by mature sycamores. Today it’s just a deteriorating shell, but when I win the lottery (once I’ve started playing the lottery) I’ll do it up and turn it into treeblog HQ. That’s the dream!

Posted in Gone for a walk

Sudden oak death and bleeding canker

There are a few tree diseases in the news at the moment. At least two of the newspapers yesterday ran the story that an avenue of 43 horse chestnuts (Aesculus hippocastanum) infected with the bleeding canker disease are to be cut down for safety reasons. The avenue at Barrington Court in Somerset, a National Trust property, is to be replanted with oaks.

According to Forest Research, parts of Europe are seeing an increased incidence of the disease. From their Bleeding Canker of Horse Chestnut page:

Until recently, such Phytophthora bleeding cankers were considered to be uncommon and were only seen in the south of England. However, over the past four or five years, the number of reports of horse chestnut trees with 'bleeding cankers' has increased markedly... The increased incidence of stem bleeding on horse chestnut is not just limited to the UK; the Netherlands, Belgium, France and Germany are also experiencing a similar upsurge.

Closer investigation of the bleeding cankers on horse chestnut has revealed that Phytophthora is no longer the primary causal agent. Instead a completely different pathogen, Pseudomonas syringae pv aesculi, is responsible for the increase in these symptoms appearing on horse chestnut.

The other diseases in the news are also species of Phytophthora: P. ramorum and P. kernoviae. Both diseases attack and kill many species of tree and shrub - P. ramorum is the cause of the rather frightening sudden oak death, which was the subject of an early treeblog post two years ago. The two diseases are in the news because the British government has allocated £25 million towards their eradication. According to this BBC article, “Rhododendrons, a carrier of both diseases, are likely to be removed in woodland to combat the problem.” Good. Rhododendron (Rhododendron ponticum) is bad news. It is highly invasive in the UK and takes over woodland through the development of a dense covering of nothing but evergreen rhododendron bushes that stifle and inhibit our native flora and fauna. I would like nothing more than to see rhododendron completely eradicated from Britain, but getting rid of it is easier said than done. It is one stubborn son of a bitch.

Uh-oh. Rhododendron at the edge of my beloved Whitwell Moor (23 May 2007).

P.S. Phytophthoras, sometimes referred to as fungal-like pathogens, are actually protists of the order Oomycetes (water moulds). They are more closely related to plants than fungi.

P.P.S. The abbreviation ‘pv’ means ‘pathovar’, “a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one or more plant hosts” (definition from Wikipedia).

Posted in Pests and diseases

Whitwell Moor perimeter wander

The enemy in our midst. Rhododendron ponticum on heather moorland. The moorland appears to be under succession by birch woodland, although Rhododendron might end up taking over instead.

Photos taken on the 23rd of May 2007.

R. ponticum inflorescence.

Looking across fields towards the village of Bolsterstone between the branches of a hawthorn (Crataegus monogyna).

Female beech (Fagus sylvatica) flowers - these will transform into beechnuts over the next few months.

The twisted and tortured-looking trunk of a stunted Scots pine (Pinus sylvestris).

A beech seedling with one pair of cotyledons and one pair of 'proper' leaves.

A nice bit of semi-natural mixed woodland. Lots of beech and Scots pine and plenty of oak off-camera. The low shrubs in the foreground are bilberry (Myrtillus vaccinium).

Posted in Gone for a walk

Sudden Oak Death - be on the lookout

Sudden Oak Death is the term used to describe the disease caused by the fungal pathogen Phytophthora ramorum amongst oaks. However, P. ramorum is not limited to oaks: it has the potential to cause disease over a range of hosts in Britain. A DEFRA information leaflet published in 2006 lists known UK hosts:

To date the full range of known ornamental hosts in the UK and Europe include species of Arbutus, Calluna (heather), Camellia, Griselinia, Hamamelis (witch-hazel), Kalmia, Laurus (laurel), Leucothoe, Lonicera (honeysuckle), Magnolia, Osmanthus, Parrotia, Photinia, Pieris, Rhododendron, Syringa (lilac), container grown Taxus (yew), Umbellularia californica (Californian bay laurel) and Viburnum. Most nursery findings have been on container-grown Rhododendron, Viburnum and Camellia plants. However, the main threat is to tree species and other ecologically important plants, such as heathland species.

In October 2003, a southern red oak tree (Quercus falcata), a native American species, was the first tree infected with P. ramorum in the UK. There have since been findings in the UK on several other oak species (holm oak, turkey oak, sessile oak), as well as ash, European beech, horse chestnut, sweet chestnut, sycamore and Winter’s bark. Infected rhododendrons have been in close proximity to all infected UK trees to date. Experimental work has highlighted other tree species that could also be at risk from P. ramorum in the UK. These include Douglas fir, maple spp., Noble fir, Lawson cypress and Sitka spruce.

Symptoms of the disease vary amongst the different hosts, but in general dieback of foliage and bleeding cankers on the trunks of trees are good indicators of P. ramorum infection. Full details can be found in the DEFRA leaflet available here [.pdf format, 873kb]. If you suspect a plant of being infected by P. ramorum, contact DEFRA immediately! (Contact details can be found in the leaflet)

Posted in Pests and diseases

Rhododendron ponticum L. - enemy of the woodland

Rhododendron ponticum is a non-native evergreen shrub species existing in the British Isles as an alien. It is an extremely important species for two main reasons. Firstly, it is superbly adapted to thrive in many British habitats; particularly woodland, of both coniferous and broad-leaved varieties. R. ponticum is ‘thoroughly naturalised’ in many woodlands, particularly on sandy podzolic soils. This prolific invader is a substantial ecological menace to the natural woodland flora and fauna of the British woodland. Its foliage is so thick that it casts a dense shadow that prevents light reaching other woodland flowers. Further, R. ponticum contains poisonous chemicals, thus inhibiting predation, and deters competition allelopathically via the secretion of acids. Secondly, it is a host plant of Phytophthora ramorum, the pathogen behind Sudden Oak Death. For these reasons, R. ponticum must be managed in order to curb its negative effects upon the natural ecology of the British Isles. Unfortunately, R. ponticum is particularly difficult to eradicate; its waxy leaves render herbicides generally impotent, it produces vast quantities of seed, and it requires much labour to chop down or uproot, it being a large plant.

The above passage is an abridged version of the introduction to an essay I am writing as part of my degree in Ecological Science at the University of Edinburgh. I just hope that people realise, if they didn't already, the tremendous damage being done to our woodlands by rhododendrons.

R. ponticum inflorescence.

Posted in Invasive species + Pests and diseases

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