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.

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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!”

A step back in time

thumbnail_map of all three oaks

So here is an aerial photograph with my three Guisborough oaks on, but what was the landscape around them like in the past?

What changes have these trees seen over their lifetimes?

Well, that is impossible to answer fully but we can have a go. Good comprehensive maps don’t go back that far but for the recent past there is an amazing website (National Library of Scotland), which is so simple to use and great fun. It has a facility where you can select an area on a modern-day map or aerial photograph and by the side you can select various historical maps and look at both at the same scale… one could waste hours pouring over maps……

 Gisborough Parkland Oak

thumbnail_Guisborough oak historic map 1

 

As you can see not much has changed in terms of the immediate landscape in the past hundred years or so.  This was as I had expected.  Also, given the broad crown of our oak here, it is obvious that it its early growth was not curtailed by competition from other trees. Rather it has grown up on open land, probably pasture, so it is likely that this land has been pasture for a good few hundred years.  I wonder if it was grown from a self-sown acorn or planted… we will never know.

However at one time the land it is on was cultivated, as there is evidence of ridge and furrow. These regular undulations are visible in the field and also on aerial photographs.  Ridge and Furrow is a pattern  of ridges and troughs that was created by Medieval ploughing.  In the Middle Ages they ploughed in large open fields with non-reversible ploughs on the same strip of land each year. So this pattern is visible on land that was ploughed in the Middle Ages, but which has not been ploughed since! I will have to get the right light and try to capture it photographically.  I wonder, does the tree predate this medieval field system or when it was a young tree did it look across an open field system with serfs toiling over their thin strips of cultivation?

 Alderman Oak

Alderman oak historical map 2

In contrast, our Alderman Oak now stands in very different surroundings than it did a century ago.  Perusing the maps, it was a rural tree, on the edge of a spinney, standing on the border of the Hutton Hall parkland. Maps show a railway line that ran between Middlesbrough and Guisborough (which is now the Guisborough Walkway). In addition there is another rail line – one which I didn’t know about – a mineral railway that probably went to the ironstone mines at Belmangate. It’s hard to tell if the tree was just north or south of the rail line. It was certainly very close. Any closer and it would probably have been felled to make way for the rail line, so it has had a lucky escape.

Today, the parkland remains and so does the little spinney next to the tree, but all the housing in new. It is interesting to see that the route of the mineral line can still be traced on the aerial photograph as a curved line of scrub. You can also see that the coniferous woodland below Kempler Wood was rough land, probably moorland.

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Also on Alderman Road, about 200 metres further down in the estate, are two beautiful oaks, one very near the road. They are in line and I had always assumed that they must be trees that were once on a hedgerow or field boundary that existed before the housing estate. But looking at this map and a more recent map from the 1960s, no field boundaries are shown, so they must have been lone oaks, in pasture perhaps. What is so amazing is that they were saved when the estate was built and not only that but no one has got rid of them since.  Although everyone says they love trees, that seems to be far from the case when a tree is anywhere near someone’s property. I hope there is a tree preservation order on them… I will have to investigate.

Roseberry Oak

thumbnail_Newton Under Roseberry Woodland historic map 1

No surprises looking at the maps of the Newton Wood and Roseberry Topping. The actual boundary of the wood is little changed. I can tell the wood is ancient (dating from at least 1600AD, just looking at its rich ground flora, and it is marked on the National Inventory of Ancient Woodlands. But how ancient is the woodland?… a story for another blog entry … and also a visit to the archives to see if there are surviving old estate or Medieval maps in existence.

The cola nut gall – perhaps!

Whilst taking a closer look at the closed buds of the Alderman Oak on 26th March to see if they were waking up yet, I noticed some small knobbly growths clustered beneath the buds at the ends of a branch. At first I thought they were just odd-looking buds, but on closer inspection they were hard and spherical, rough and scaly… perhaps some sort of gall?  I am familiar with a few oak galls –  the oak apple, oak marble and knopper gall but that’s the extent of my knowledge. Galls are changes in plant tissue as a response to the activities of another organism, usually a species of wasp but it can also be due to fungi, bacteria or a nematode.

$_35

 

Looking through my Guide to Britain’s Plant Galls, I discovered there are perhaps around 50 different species of gall associated with Pedunculate and Sessile Oak, and that I needed a specialist guide. I downloaded a keyto oak galls which was a bit impenatrable, so instead I posted a photo on the facebook group  Insects of Britain and Northern Europe which has over 12,000 followers.

DSCN2327

Within minutes I received a response that it was possibly the cola nut gall. Googling photos this is probably right. They are small, hard, brownish, under 15mm diameter, growing in clusters, rough and near to the oak leaf buds.  What is especially interesting is that they are caused by a gall wasp (Andricus lignicola) which has a fascinating life cycle. The gall on pedunculate oak is caused by the asexual generation. The adults emerge in the autumn and they then lay their eggs on a different species of oak – the Turkey Oak – where the larva produce tiny egg-shaped galls which the sexual adults emerge from in March to start the cycle all over again. The species has only been recorded in the UK since the 1960s!

Taking a closer look at my galls, I think these then must be from last year, but I can’t see any hole where an adult wasp has emerged. These are recorded as being near the base of attachment.  I decide to chop one in half to have a look inside. After trying all the kitchen knives from the vegetable and carving knife to the bread knife, this proved impossible – they are far too hard to crack.  I even tried using my teeth but to no avail. I managed to escape without any knife injuries thankfully.

Oaks have more galls than any other European plant species according to Michel Chinery, so I hope to find lots more on my oaks this year. Different species occur on different places including acorns, leaves, catkins and bark, and also, I was surprised to discover, on roots. But as I don’t plan to uproot any oak trees, I will be unlikely to discover the latter.

Introducing three Guisborough oaks

So my idea is to select three very different oak trees to track.  I want three very different habitats – urban, parkland and woodland – as oaks are important components of all three habitats and also they can grow very differently in these environments. In addition I am  looking to choose different ages or life stages of oaks.

English Oak is long-lived and it is often said that it has three life stages – three hundred years growing, three hundred years simply being and three hundred years gradually dying! I vaguely recall a saying/poem to that effect but can’t find the source.

So I wanted an oak  in each of these broad life stages so here we have it – come and meet my three oaks…

Alderman Oak – the urban grandfather

Gisbrough Hall Oak – the parkland beauty

Roseberry Oak – the  young skinny socialite

 

The Alderman Oak– the suburban grandfather

This grand tree sits on the corner of Alderman Road and Hutton Lane in Guisborough. It sits a little back from the road, and it’s easy to drive past it without noticing it. It isn’t an especially large tree, its crown is quite small, but on closer inspection it has a fascinating trunk. It would appear that during its early growth the trunk branched (or was cut) and then as the two trunks regrew they joined again.

DSCN2292

The oak has lost some major branches. It is hard to tell if these were lost due to natural decay or were cut and removed at some point. Whichever it was this has resulted in some major rot holes.

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In addition the loss of bark and internal rot, with evidence of some sort of wood-boring beetle and plenty of spider webs.  The trunk is full of burrs too.

 

All this indicates that we are dealing with quite a mature tree. In the past (and dare I say it – some still hold this view) that these burrs, rot holes, crevices, lumps and bumps   were considered as deformities. Of course if you are growing oak for timber this tree would have limited value for wildlife it is a fantastic. This tree is probably providing a microhabitat for  many species of bacteria, fungi, moss, lichens, as well as specialist  invertebrates , and  possibly a roosting/nesting site for birds and bats!

Until recently well-meaning tree surgeons would actually fill rot holes and cavities with cement, as if they were tree dentists but now due to the huge amount of research on the  habitats that old and dying trees  provide theer is generally a more enlightened approach…. but more of that possibly in a later blog…..

Gisborough Hall Oak – parkland beauty

cropped-DSCN2316

I think that you will agree that this  is a magestic beauty, an English Oak in its prime , and growing in a parkland setting, free from competition from other trees it has a beautiful tall and wide  crown.

No I haven’t spelled Gisborough incorrectly, as this oak is growing in grazed pasture parkland opposite Gisborough Hall. I chose to use the traditional spelling that both the Hall and Priory retain.  I pass this tree on my way to work, and it is one I always look out for, but I have never been in close contact before. It is growing just metres from the Cleveland Way public right of way, so I didn’t need to stray far from the track.

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It is a tall tree  with a fairly straight trunk with few burrs, and it certainly has a very different charcter and is likely to be younger than the Alderman Oak.

 The Roseberry Oak- young skinny socialite

The closest oak woodland to Guisborough is probably that of Newton-under-Roseberry. This is an ancient woodland (that is recorded as having continuous woodland cover since 1600AD) at the foot of our iconic Topping.  I know the wood fairly well, having surveyed it as part of the Tees Valley Ancient Woodland Ecological Condition project a few years ago but also I take a pilgrimage each year to see the bluebells, which are awesome. So the plan was to select a tree from here, one that had lots of neighbours, and to contrast with the other two oaks, one that was fairly young.

add picture from a distance

Well, easier said than done! The other two trees had jumped out at me. It is somewhat harder to pick a “typical tree” from a woodland…  I wanted to avoid the larger trees that adorn the edges and clearings and chose one that was a real woodland tree, but easier said than done.

NuR 4 April showing woodland habitat

I selected this one,  for no particular reason, except it was very thin and weedy and surrounded by larger trees. It has  a slender trunk and very unusually just one bol (major branch),  and this  reaches up to the sky at an odd angle in an attempt to reach the sunlit canopy. Although the trunk is only 80cm in diameter (at 1.5m from the ground), the tree is probably far from young and if you look up into its single trunk there are signs of rot.

 

Also, this poor tree appears to have axe marks in it. It would seem that someone at some point has tried to fell the tree. Looking at the damage it is more likely to be a result of vandalism rather than a failed forestry operation.

NuR 4 April tree 1 close up of ake cut

So that is the cast of three trees for this blog, although other oak trees in other localities may on occasion be making guest appearances.