In full leaf

 

I drive past my Gisborough Park oak twice a day, en route between home and work, but it is a surprisingly fast road with no safe parking so I have neglected to visit for a while. But each day I have been noting how it has progressively developed a full crown of leaves. Today (23 May) I realise that it has lost its fresh olive tint and is now actually green.

It’s a lovely sunday late afternoon, and after a day slaving over a hot computer, I decide a stop off to visit the Gisborough Park oak is in order.

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Although the leaves are now fully formed, in the sun they still have that wonderful spring green about them which I know they will gradually lose as the season progresses.

Most of the male catkins have dried up but they remain on the odd branch. I was going to write a blog about the flowering of oak, but my friend Heather Kelly has just published an excellent one – here is a link.

The buttercups are now flowering, along with germander speedwell, and I notice the  delicate umbellifer pignut for the first time. The grassland is nutrient rich and has been improved as a rich grazing pasture so it is a pleasant surprise to see pignut scattered through the sward.

Under the boughs of the tree, the flora is characterised by annual meadow grass and chickweed, with a few clumps of nettles – all indications of disturbance and nutrient enrichment.  I had noticed earlier in the year when the pasture contained sheep, how they congregated under this tree for shelter (and company perhaps!), which accounts for the flora here.

Gazing up into the tree I am surprised and delighted to discover the cotton wool gall growing, just two of them, but I shall have a story about that special gall in a forthcoming post!cotton wool gall.jpg

It’s too lovely an evening to rush home so I take the opportunity to have a look at the other oaks in the pasture.  Although probably of a similar age, each one is so different, all individual in their growth patterns, lost limbs etc., all telling their own stories.

It wasn’t until the May bank holiday weekend that I was able to catch up with my Alderman Road oak.

The tree is now completely clothed in green – so much so that it makes me realise just how much leaves obliterate the structure of  a tree.

extra growthAnd it’s not just that the leaves have opening. There has been a massive growth spurt, with a good 10 cm of non-woody growth at the end of the twigs.

 

 

 

The leaves now seem incredibly large too and are now getting quite a tough waxy cuticle. On further examination,  some are sticky, a sure sign that aphids have been active. The stickiness sucks up the sap in the leaves by piercing the phloem tissue.  But the sap is so rich in sugar and low in nitrogen that the aphids must consume a lot of sap to meet its nutritional requirement for protein, and the sugar is excreted from their rear ends as tiny droplets of honeydew.

I notice that there are currant galls on the leaves but none at all on the male stamens. I have discussed this phenomenon in a previous post, but I still wonder why on some trees the gall wasp lays it eggs on stamens and in other trees on the leaves but on any one tree it is either one or the other.

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I spy a few oak apples and cola galls, so that is three different species of galls that this one tree is harbouring so far this year.

Inspecting one’s leaves  I find a little caterpillar-type creature, which appears to have made itself a protective tent. But before I can examine him closely, he disappears, leaving his protective shelter behind.

I also notice that there is a pattern of dieback on some of the leaves that is confined to the margins. I wonder if it is caused by an insect but can’t find any, so it is a mystery.

edges of leaf dying

Looking up into the tree there are a few large interesting rot holes which will probably be home to a host of saproxylic invertebrates  (feeding on deadwood). The spinny behind the wood is full of flowering cow parsley, bramble and hawthorn, which are vital food sources for the adults of many deadwood insects, after they have spent their larval life in the timber.

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I think next time I visit I need to bring a sweep net, a pooter and some collecting jars.

Happy Oak Apple Day

Today, the 29th May is “Oak Apple Day” or “Royal Oak Day.”  This was, until it was  abolished in 1859,  a public bank holiday. It was celebrated by wearing an oak leaf or oak apple in our attire, dresings and decorating trees and no doubt engaging in feasting, drinking and general merrymaking.

charlesOak Apple Day celebrates the restoration of  King Charles II to the throne on 29th May 1600.

“Parliament had ordered the 29th of May, the King’s birthday, to be forever kept as a day of thanksgiving for our redemption from tyranny and the King’s return to his Government, he returning to London that day.”
Samuel Pepys’ Diary – 1st June 1660

It was declared a public holiday, but why the connection with oak and oak apples? Well, it is likely to be associated with the legend that after the Battle of Worcester on 3 May 1651 the King hid in the famous Boscobel Oak.

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Lid of the Boscobel Chest with deep relief wood carving showing soldiers and dogs at the oak –  Boscobel House, English Heritage

But why oak apples, which is a gall? 

Despite being abolished as a public holiday in many rural parts of England, the day was celebrated with local customs right into the 19th century. In the 1890s many railway engines were decorated with boughs of oak anda widespread custom appears to have been  the practice by children of whipping any of their peers with nettles that were not wearing a sprig of oak leaves or oak apples – nasty!

Oak Apple Day does live on in Worcestershire, where the county’s museum service have revived the day, hopefully without the nettles.

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 Finding the first Oak apple of the year

Whilst descending the steep steps down through Newton Wood, Heather noticed a beautiful single oak apple, attached to an oak that was just coming into leaf.

Whilst familiar with oak apples it was usually when they were old and brown. Neither of us had seen such a lovely red and rosy one before. We plucked it for further investigation.

Although it was less than an hour till we had got home, drunk tea and retrieved it from my coat pocket, it had surprisingly shrivelled somewhat.

All I knew about oak apples was that they are galls and caused by a gall wasp and were used in the past to make ink… so I thought I would do some research…

The gall is produced by the wasp Biorhiza pallida. In early spring the female injects, using its ovipositor, about 30 eggs into the vein of a growing leaf, triggering the oak to produce the gall – plant tissue – that provides both food and shelter for the growing larva.

Despite the aid of a x40 lens, I couldn’t see any grubs, just plant tissue. I imagine this is because, given the time it was picked ( 30 April), that it was very fresh and perhaps the larvae were still eggs or too small to see. So I will have to find some more oak apples and dissect them throughout the summer!

Biorhiza_pallida_maleBut the story is far more complex and interesting that I ever could have imagined.  The life cycle is that the larvae,  by summer, nibble their way out of their chambers and emerge.  The winged males and females mate and then the female lays her eggs, not on an oak leaf but underground on the rootlets of oak to produce an underground gall. Here the larvae feed for around 18 months, and all the adults that emerge are female and wingless. These poor wingless females, then crawl their way up the oak in Spring to inject their eggs into the oak leaves, so starting the two-year life cycle all over again. It is unlikely, as I don’t plan on digging up any oak trees, to see this underground gall, or the tiny wasp, so here are some photos from good old wikipedia

Well, now I seem to finding oak apples everywhere. Below are photos that Nigel Dobbyn took for me from Newton Wood on 8th May.

Project idea for later on in the year! Find some oak apples after the wasps have emerged and have a go at making ink!  I think that although many sources say that ink is made from oak apples that  it could  the marble gall which some people also call oak apples, So I will try with both.

As the spring progresses I seem to notice oak apples everywhere, is it an especially good year for them or is it just that I am noticing them more, They soon swell, looking considerably less attractive and the  larva are very  much apparent, appearing as little white grubs.

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I was at the  Castle museum  in Knaresborough this weekend and came across this  tapestry that is believed to have been  made in the 1660s. It’s beautiful beadwork depicts King Charles II and his wife Catherine surrounded by the leaves of oak…. well they certainly look like oak leaves to me!king chales neddlepoint.jpg Below:Photo and words by Nigel Dobbyn, from Newton Wood

nigel oak apple with poem

In search of ancient oaks in Ingleby Botton

Well, yes, I know this is a blog about three Guisborough oak trees, but sometimes it’s nice to have little adventures looking at other special oak trees as well.

The Woodland Trust’s interactive Ancient Tree map is a great place to start investigating. Records seem a lot more sparse in the North of England which may be the result of there being less ancient trees or fewer people recording them. It is probably a combination of both.

So on the 20th May I was joined by Jacky Watson on the edge of the Cleveland hills to hunt down a renowned ancient oak at Ingleby Botton and also to try to find the Medusa Oak on the Ingleby Incline. Megan and I had tried to find the Medusa Oak last month but it eluded us.  By the way, it is Ingleby Botton not Bottom (in case you think it is a typo). I always thought it was bottom, being at the base of the hills but it is Botton, which is dervived from the Norse word botn, which means the innermost part of a landform such as a valley or fjord. This aptly describes this deep valley that cuts into the moors.

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We are distracted from our mission even as we pull on our walking boots and make difficult decisions on the “take waterproofs or leave in car” debate by the flamboyant ariel acrobatics of swallows and house martins. Jacky expertly points out how to distinguish between them, as each year I seem to need reminding how to tell apart the swallow/swift/martin triumvirate…

And we are off, to be distracted again by a series of enchanting copses of alder trees that have developed in the wet hollows between the pastures. Most of the alder trees are multi-stemmed, and although this could be a result of coppicing, carried out several decades ago, it seems to me that I only ever see alder as multi-stemmed and wonder if that is it natural form.  Last month these were bare stark trunks. Now their ridged leaves are burgeoning and below is a carpet of bluebells and a scattering of stitchwort. Both of us are unhappy with our attempts to capture their beauty on film –  bluebells en masse are notoriously hard to photograph.  We feel the urge to explore these little fingers of woodland but they are well and truly fenced with barbed wire… and anyway we are on an oak hunt.

At the point of where the Incline certainly does indeed incline rather steeply we take the track to the right and within a few minutes spot what looks like our oak.

And what a tree! Its true magnificence is not apparent from the footpath. It’s not until you get up close that you realise that it isn’t three trees but one single tree, and that the trunk has hollowed out to such an extent that  you can walk through it with ease.

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We spend time exploring all its nooks and crannies. It certainly ticks all the boxes for having the characteristics of an ancient tree as defined by the Ancient Tree Forum, having a wide girth, rot holes, decaying heartwood, a reduced crown, fungi, dead branches, loose rough bark, missing bark, cavities and sap runs.

This amazing oak doesn’t appear to have a name, which is surprising as it is such a feature. It is simply marked on the Ancient Tree Hunt map with the reference number 38805.

The oak sits unobtrusively between the track and conifer plantation behind. Most of this has been felled, their stumps remaining admist the natural regeneration of rowan, birch and gorse. But what is surprising is that this tree survived  when the plantation was first developed. Having just returned from a conference on wood meadows and pastures in Sheffield I saw many before and after ariel photographs of coniferous afforestation on wood pasture sites and in which ancient trees were routinely felled.  Our oak, in its younger life, was likely to have been an open grown oak and had a lucky escape, somehow escaping being felled. Perhaps it was too near the path to bother with, a forester went home early or maybe decided it was sacrilege to terminate this veteran.

It would be easy to feel anger at the practices of the Forestry Commission. Many have described their early work as ecological vandalism and unsympathetic to the historic or ecological landscape. However, it is important to remember when and why the Forestry Commission was set up. Woodland cover stood at around only 5% at the beginning of the 20th century with the country importing much of our timber needs. During the First World War, and no longer able to rely on imports,  Britain struggled to meet demands at home and also for timber for trench warfare. The government set up the Forestry Commission in 1919 to build and maintain a strategic timber reserve and they were given extensive freedom both to acquire and to plant up land.

Now the economic drivers have changed. I was a member of a board of  “Forestry Commissioners” for the North East of England for four years, until 2015, part of an advisory committee to advise the Forestry Commission on strategic matters and areas of conflict.  What I saw was a tightly run, evidence based, forward thinking organisation that had embraced a great deal of change and was balancing the needs of the commercial forestry industry (an important economic driver in Northumbria) and  ecological and recreational interest – a complex challenge.

It is only since the 1970s that the term ‘ancient woods’ and ‘veteran and ancient trees’  has been coined and their value in terms of biodiversity and cultural heritage recognised.  George Peterkin (an eminent woodland ecologist) said at the Wood Pasture Conference that in his days at the former Nature Conservancy Council, these woodlands were termed ‘mature timber habitats’ and that he and the woodland historian Oliver Rackham came up with the term ‘veteran trees’ in the 1970s.  He considers that by coining these terms, it helped to clarify the concepts that they represent, enabling their value in terms of biodiversity and cultural heritage to be more widely recognised. The terms caught on, as did interest and research into ancient trees.

Anyway, back to our tree, a relic of a past landscape!  It appears to be the only mature  tree around. Next to it was the most amazing tree stump. It was so decayed that it was impossible to tell what species it had been when alive, if it had been felled or had succumbed to a natural death. It was a mass of lichen and fungi and heartrot. Growing amongst it was new life in the form of honeysuckle and wild stitchwort.

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The battery of my camera decided to die, and Jacky has kindly let me use her photos – her camera has a much better zoom anyway.

Now, being a good conservationist, I am well aware of the need not to disturb dead wood micro habitats, but who can resist taking a peek under bits of loose bark and turning over logs… which we carefully replaced. However, one bit of bark on the trunk does come away on my hands, and I have to place it rather guiltily to the side of the tree.

P1080878We investigate a log that has now lost its bark next to the tree. It is full of life, with spiders’ webs, millipedes and  a fast-moving centipede. Some very large holes demonstrate that it has been the home to beetle larvae that have emerged into adulthood. They are large exit holes, much larger than the ones scattered around the heartwood of the trunk.

P1080879After careful consideration we decide that this log doesn’t belong to the oak as we can see no branch stub and after hunting around a bit higher up the slope we realise that it is the same dimensions of some others in the felled plantation, so it is likely to be from a more recent conifer.

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We sit down in the springy sward in he shade of the oak to have our picnic, greater stitchwort and ferns unfurling around our feet, and feel grateful for this day, the spring, the sunshine and being in this beautiful landscape. We notice a few small seedlings of rowan and birch. Between bites of cheese and pickle sandwiches (caramalised onion chutney courtesy of  Lewis and Cooper, highly recommended), I mention to Jacky about how difficult oak finds it to establish under its own canopy and how uncommon it is to see an oak seedlins or sapling. She points out one a few yards away, which we coo over and then we see a second, a third, a fourth! I feel the urge to put a little protector around them to keep off the nibbling teeth of rabbits and deer. These are descendants of this mighty tree and demonstrate that despite its old age and gnarled appearance, it is still producing viable acorns.

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We contemplate how old this tree could be. it is recorded as having a girth of 10.75m but although there are all sorts of tables and equations one can use to correlate the girth of a tree species to its age,  it is an inexact science. Trees, even of the same species, grow at different rates, depending on their environment and their rate of growth and this can also change throughout its lifetime. Various people have guestimated that this oak may be 400, 600 or even 800 years old. Who knows which is the best estimate? I feel no need of a definite figure though – it all adds to the mystery of this gnarled, knobbly old tree, which may continue to live for a few hundred years yet.

We decide to continue our expedition to find the Medusa Oak. We have an eight figure grid reference from two sources: the Ancient Oak Map and Mick Garrett on the Geograph website.  However, yet again the tree eludes us. It is somewhere in the rocks above the footpath amongst the tangled regrowth of rowan, birch, gorse and sycamore that has replaced the coniferous plantation. However, the terrain is so steep and rocky and covered in trees, it is impossible to search. Jacky scans the foliage with binoculars to see if she can pick out oak leaves but no luck.

But it isn’t a completely wasted journey.  We stop to photograph a striking patch of  bugle, its deep purple foliage and lilac flowers contrasting with the spring green leaves and  tiny acid yellow flowers of crosswort and whilst she is preoccupied with that I watch a lazy bumblebee in the nearby bluebell. But the more I study the bee, the more odd it looks. Somehow its body is too long and its face isn’t quite right… and then I notice its wings. After a while it pulls its head out of the flower to reveal a long proboscis, and I realise that it is a bee fly, which I have heard about but never seen before. It is obviously ambivalent to all the attention it is receiving and Jacky is able to photograph it:

 

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On the way back we see a tiny oak that is rooted around a boulder which may have been what the Medusa Oak started off as a few hundred years ago. And then it starts to rain. Back home for tea!

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Bluebells, thoughts on red leaves, a lemon top and a currant gall

It may only be a week since I last visited Newton Wood, but even within seven days there is a noticeable difference in the greening of the trees when viewed from the farm gate.

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 Beautiful bluebells

Despite it being a cold, dull grey afternoon the carpet of bluebells, now in full  bloom, warms our hearts, carpeting the slopes of the woodland in an intense blue.  Newton Wood is probably the best and most well known bluebell wood for miles around.  Bluebells, along with primroses, are one of the few wild flowers that almost everyone can recognise and name. Their wonderful colour and scent, both delicate and demure as individual plants, but spectacular in their mass performances each spring, make them an iconic ambassador for our native flora. The wonderful Woodland Trust is using this model species to highlight enjoying and conserving our precious woodlands, with their BIG Bluebell Watch.

The Woodland Trust have a useful and fun quiz to check if you can tell native and Spanish bluebells apart. They have found that around 1 in 6 bluebells found in broad-leaved woodlands in the UK are Spanish or a hybrid rather than native. The ones here all appear to be native.  Whilst it may seem somewhat xenophobic to want native rather than Spanish bluebells, it is worth considering that Britain is vital for the future of the bluebell (Hyacinthoides non-scripta) as we have over half of the world population! The other threats to bluebells are loss of habitat and uprooting. Since 1998 it has been illegal to  collect and sell bluebell bulbs from the wild, a law that was brought in response to unscrupulous people destroying bluebell woodlands for the sale of bulbs.

Bluebells are not the only woodland plant busily growing and flowering before the canopy closes. Wild garlic is now clothing the damper slopes and in damp gullies opposite-leaved golden saxifrage clings to the rocks.

 Why are young leaves in oak and many other species tinged red?

All the oak trees are now at some stage of leaf, but there are still noticeable differences between individual trees, and you can see the differences in colour, the leaves becoming greener as they expand.

The very first and early leaves can be pink or even red and this is in common with many tree species, such as sycamore and hawthorn. Heather Kelly and I discussed this on our visit to the wood last week and she believes that it is was possibly an evolutionary response to protect against predation, too much sunlight or frost damage.

Investigating this further, the red is due to anthocyanins. These are flavonoids pigment compounds which absorb blue and green light, therefore appear red. Later they are masked by the chlorophyll. There appear to be three theories about the adaptive significance of why young leaves are often tinged red:

 

  1. Protection against insect herbivory by the red colour being cryptic to those herbivores that are blind to the red part of the light spectrum
  2. Protection against high levels of light, UV and/or cold
  3. May be fungicidal

 

I can imagine that the first explanation is significant as anthocyanins do have an  antioxidant role, snapping up tissue-damaging free oxygen radicals in plants that are produced as a result of stresses, such as overexposure to UV and extreme temperatures.  And herbivory may play a role too as reported in Trees Physiologist  in a study of Quercus coccifera by Karageeogou & Manetas in 2006.

As we look at the oaks and bluebell to a backdrop of chiffchaff and great tit calls, we hear the drumming of the greater spotted woodpecker, a familur bird of oak woodlands. More suprising to us, the green woodpecker – with its unmistakable  raucous laughing ‘yaffle’ call. I associate them with meadows in Oxfordshire, where I often saw them feasting on ant nests.  Sadly we don’t see either bird.

We come across an extensive complex of tuinnels, right next to a major footpath… no prizes for guessing who lives here!

It starts to get cold and rainy and the light is poor so the thoughts of a fire and a cup of tea pull us back to the carpark. Which is why I am very surprsied that Nigel has a lemon top ice cream… despite it being a really cold day and not by the sea!

Nigel with his lemon top

But that wasn’t quite the finish, as I had plucked a couple of twigs to closely examine the male catkins at home (in the warmth of the fire, accompanied by a pot of tea), when I noticed what appeared to be a translucent hard blister on the underside of one of the leaves…

Looking through pictures of oak galls, I wondered if it could be the currant gall. It occurs on the male stamens of oaks and is caused by the gall wasp Neuroterus quercusbaccarum, but I did find a reference to it being found on young leaves as well. So I posted a pic on the facebook group “Insects of Britain and Northern Europe” and within minutes a helpful chap called Robert confirmed that it was indeed the sexual generation of Neuroterus quercusbaccarum and that the female does lay eggs on the leaves, which he felt depended on what was first available to the females after they emerge from their larvae after winter. I am still keeping a lookout for these currant galls in their more usual clusters on the catkins.

 

An amble in Newton Wood – lichens and more

The last day of April and it’s about time to visit my spindly oak tree in Newton Wood.   Joined by my friend Heather, this will be a good opportunity to investigate the lichens on the oaks there. Heather and I did a day course on lichen identification at Malham Field Studies Centre a few years ago, but the main thing we learnt was that lichen taxonomy is incredibly tricky.

newton wood coming into leaf

Leaning on a farm gate we gaze across to the wood, and you can pick out various tree species coming into the leaf. The wood’s canopy is mainly oak, giving a haze of olive green, contrasting with the mid green of the occasional sycamore. From this distance the wood reminds me of Enid Blyton’s mystical  “Enchanted Wood”, the trees whispering their secrets to each other.

A sunny Sunday afternoon is not the best time to visit Newton-Under-Rosebeerry; the car park is overflowing with folk intent on climbing Roseberry Topping, which magnetically sucks people streaming to its summit. But once we are away from the main track the wood is surprisingly peaceful.

Once in the wood we are wrapped in a womb-like woodland world. We are bathed in shades of green – above in the canopy but more below our feet and, as it is a steep slope, all around us too.  This wood is so magical, especially now, in full Spring with the heady scent of the bluebells, spiced with wild garlic and with rich undertones of decaying leaf litter and damp mosses.  You can almost feel the growth all around you. It feels like a race towards the sun.

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Looking down the bank, what strikes you is that the oaks are mainly small and of a similar size and age. There are some statuesque oaks, mainly on the edges of rides, which are not only older but had room to spread into their full glory. These woodland trees are a bit like commuters on the London Underground – crammed on a packed train, standing straight with their feet together and arms by their sides, uncomfortable with the lack of personal space.

What is also noticeable is that the understory and shrub layer is sparse.  This is a common theme in British woodlands today, with the main cause being grazing by deer. There is the occasional clump of dark green holly and saplings of rowan trees above the carpets of bramble and bluebell.

woodland bank looking upOn a casual inspection, no oak saplings or seedlings can be found, but plenty of sycamore. These sycamores are very young, their early  leaves already fully expanded and grasping at the light that oak leaves of the canopy have not yet obliterated.  Unless these saplings are removed now, this wood will become a sycamore woodland.

We are distracted from our quest of lichen hunting by the carpets of wood anemone, studded with greater stitchwort, and the occasional splash of the pink flowers of red campion and small but stately spikes of bugle.

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Patches of violets are still in flower on the steeper banks, but no primroses, and we note an absence of wood anemone.  It is noticable that on damper areas the bluebells give way to swathes of wild garlic and wood rush. Ever-present is bramble, its new pale green leaves, tinged with red, contrasting with the dark green of last year’s growth.

A closer look at lichens on oak

So, armed with my amazingly cool x40 magnification hand lens (which has its own light) we take a closer look at an oak trunk.  To the naked eye the furrowed trunk has been dusted with a grey/blue powder, intermingled with green.  The grey blue is a lichen and the green an algae. Under the hand lens the bark becomes a more three-dimensional micro landscape. The furrows and ridges are deep and  the vertical and horizontal surfaces clothed in the same lichen and algae. The one coating the trunk is a crustose species… which may or may not be Lepraria incana.

Lichens are uber complex and cool! They are an intimate symbiosis of a fungus (mycobiont) and an algae (photobiont). Actually the photosynthetic partner is not always an algae and can be a cyanobacterium (a bacterium that can photosynthesise). The result in not simply a combination of the two organisms but has a growth form that is totally different from that of either partner. Lichens can be divided into three broad types according to their structure:  Crustose (encrusting), foliose (flattened species with leaf-like lobes) and fruticose (shrubby branched species with a single point of attachment).

We find that an oak in a clearing in full sunlight has a lot more lichens on its branches, but we admit we are stumped. We think we can identify down to genus – for example, we find a foliose Parmelia species which is possibly Parmelia saxatilis, an orange lichen that is a Xanthoria species and a Cladonia species, which does have distictive pixie cup-like structures  which could be Cladonia conicaria or macilenta.


We find a tiny sample of a fruticose lichen, but we can’t decide if it is Evernia prunastri or Ramalina farinacea, so we sit and enjoy the bluebells and rather spectular view instead!

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It’s hardly surprising that we are finding these lichens so tricky – after all there are thousands of different species and 324 of these have been recorded living on oak trees.    Our two native oak tree species have more species of associated lichens than any other tree species.

Although we could not identify them we did find six different species of lichens on one small branch of an oak tree, pictured above. Some ancient trees have been recorded as supporting over 30 species on a single tree.  This isn’t surprising as older trees will have a greater variety of micro-habitats.

Anyway, the lichens of Newton Wood are not going anywhere, so there is plenty of time to learn more about them…

 

 

 

 

 

Oak before Ash, in for a splash?

Oak before Ash

We’ll have a splash

 Ash before Oak

 We’re in for a soak

 

This quant old country saying is still widely known today, and whilst not a scientific way to predict summer rainfall, it does demonstrate a long-standing interest in the variability of seasons from year to year and how trees respond differently to it.

 ash bud burst 19 April 17Ash tree at Preston Park on 17 April showing black buds and emergence of male caktins

From my casual annual observations, Ash is even more of a sleepy head than Oak. It always seems last in the spring sprint for leaf growth, and as it loses its leaves early in the autumn too, it amazes me that the species is so widespread and succesful.  So is Ash ever out first and if so has this changed in historical times?

naturescalendarphenologyWell there is quite a bit of data around to explore! Nature’s Calender, coordinated by the Woodland Trust, is a fantastic citizen science project where thousands of people throughout the UK monitor signs of Spring.

 

robert mashamBut the study of phenology (nature’s reponses to seasonal changes) has been recorded by naturalists for  a fair few centuries. Whilst their data isn’t as extensive, these nature diaries are valuable observations with which to compare more recent data.

Robert Marsham is considered to be the father of phenology. He  recorded 27 signs of spring, starting in 1736 and continuing for over 60 years on his English estate. Successive generations of his family added to his work until well into the 20th century

 

So back to our original question about Ash and Oak. Using phenological data from Nature’s Calendere there has only been a handful of times in the last 50 years when Ash has beaten Oak, whereas in the 18th Century this was much more frequent.

The Field Studies Council analysed data on bud burst of the two species between 2000-2016 and compared it to meteorological data and in doing so they found a correlation between years when Oak came into leaf first with those which experienced a warmer springs.

So the increasing occurrence of Oak coming into leaf before Ash appears to be result of warmer spring temperatures. Kate Lewthwaite of the Woodland Trust says “For every 1°C rise in temperature Oak gains a four-day advantage over Ash.”

But why and how do the two species differ in their response to warming temperatures? I can’t seem to find much on this apart from the FSC blog: “The relationship between the timing of bud burst of Ash trees and temperature is much weaker. So as springs get warmer the Oaks come into leaf earlier and earlier.  Ash trees do too, but not as quickly as do the oaks – they’re being left behind.”

So is Oak a climate change winner? Or does it make any ecological difference? Many sycamore in leaf Guisborough.jpgsycamore trees are now in full leaf whilst my oaks are just starting to unfurl their first leaves, and the black buds of ash are still tightly shut. Does this early bud burst in Sycamore give them a competitive advantage? As with most things in nature I expect there is no simple answer, but one that depends on a more complicated and unrelated set of factors…

 

 

 

Sycamore Guisborough 26 April

 

And what difference could it make to the many species of insects that feed on oak? I imagine this may have particular significance for species such as the winter moth larva that emerge with the first flush of Oak leaves.

I uncovered some research that does suggest changes are afoot with work by Marcel Visser et al indicating that warmer springs disrupt the synchronicity of oak and winter moth phenology. This is a strong indication that rapid changes in temperature patterns may affect ecosystem interactions more strongly than changes in mean temperature…

Frustratingly, as I am neither a University academic or student I can’t access scientific publications easily and can just read tantalising summary paragraphs online.

I will be keeping a look out for winter moths and the oak leaf roller moth larva as the  leaves of my oak trees unfurl this Spring.

 

 

 

 

 

Wake up sleepy head!

When starting this blog on 25 March,  my oaks were sleeping, their buds dormant… but not lifeless.  These clustered buds have within them the tightly packed, unexpanded leaves made last summer and all curled up ready for Spring.

Oaks are like the teenagers of the deciduous tree world, staying asleep whilst others are waking up.  By the end of March, the hawthorn is in full leaf in many hedgerows, the sycamore is coming into leaf and horse-chestnut and rowan are gracefully unfurling, whilst the oak and the ash decide to sleep a little longer!

By the 4th April the buds on the Alderman Oak appeared to be elongating!

Waking up at last…

alderman oak 4 april showing elongating buds

By the 8th April, it can definitely be called ‘bud burst’.

alderman oak 8 April bud burst

The following day, driving on the Whitby Road past the Gisborough Park Oak, the whole tree had a faint olive glow. I pulled up (I must remember not to park at the entrance to the lodge, as the Estate are not happy about it) and raced to my oak. It’s a bit frustrating that I can’t actually reach any of the branches, but on the south side of the tree are the very first recognisable leaves bursting out. Interestingly, on the north side, they are not so advanced, perhaps a day or two behind.

parkland oak first leaves close up.jpg

South side of the tree below:

alderman oak looking up in branches

Upon visiting my Alderman Oak with Megan on Easter Friday (14 April), not only were some of the leaves starting to unfurl but also the male catkins were making a show.

Alderman Ok leaves and unruling catkins.jpg

Megan was surprised to discover that oaks had catkins, and I image that, being the same green as the leaves, they often go unnoticed (more in a later blog).

So all this looking, watching and waiting for oak buds to burst and now having new eyes and observing all the trees more closely as I am driving around (whilst still looking where I am going) got me thinking a bit more deeply about the environmental cues for  bud burst and the physiological mechanisms involved. Phenology – the study of seasonal changes – is a fascinating subject and with climate change occurring, a vital one.

Many species of oak are evergreen. These are species in southern Europe and the warmer parts of North America,  but our Quecrus robur is deciduous.  This is an adaptation to surviving cold winters. However, loss of leaves in winter means the growth of  a completely new set of leaves in spring is needed before the tree can capture energy by photosynthesis again. So how do oak trees know when it’s Spring and time to wake up? Who sets the alarm clock?  Temperature and day length both change in Spring. For  oak it isn’t simply warm spring temperatures that trigger bud burst, as if that was the case an early warm snap in winter would have the disastrous effect of leaves emerging only to be damaged by further frosty temperatures. Oaks are not so easily fooled and require a period of prolonged exposure to cold before their dormancy is broken by warming spring temperatures.

So how do oak trees “feel” changes in temperature?

Digging right back into the dusty recesses of my brain, and trying to remember plant physiology lectures from 30 years ago, I vaguely recall that the plant hormones – abscisic acid, gibberellins and cytokinins – are important for control of plant processes and are responsive to environmental triggers such as day length.  But I can’t recall much more than that – well it was a long time ago – and I was probably dozing at the back (actually I was always a bit of a swot and likely to have been in the second row – being in the front row was far too swotty for anyone, as a result it was always empty). Continue reading “Wake up sleepy head!”