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Weeding out Silver Birch

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Postby Rich » Sat Jul 31, 2010 7:45 pm

Hi,

The cant I cut in the winter is actually coming back quite vigourously despite the attentions of some athletic 'high jumping' deer! I'm just wondering about the best way to encourage the hazel, hornbean and chestnut over the silver birch. The cant probably hadn't been touched for 40 or 50 years judging by the birch which were in there. Encouraged by the coppicers 'magic wand' of immortality, these aging specimens are now coming back faster than any other, do I chop them back now and keep on top of them the rest of the growing season or just once at the end of each season till they get overshadowed?

Rich


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Postby carlight » Sun Aug 01, 2010 4:44 pm

hi ,would have thought that cutting them now is best .(or even a bit earlier next year).Try and cut them tight to the stool .

(if cutting in the non-leafy season is kinder to coppice ,then cutting in the leafy season is mean .- sugars / storage / roots - and all that .)


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Postby Rich » Mon Aug 02, 2010 7:27 am

Yes I was thinking the same, strange how trees don't do as you want them to! I killed my mother's silver birch in her garden, pollarding it last year. It was about 45 years old and had been pollarded 20 years previous, so I took a chance and chopped it all off at about 12 feet. When I coppiced the even older birch this year, I sacrificed a lot of chains getting the stumps down to ground level thinking they propbably wouldn't come back. Most of them seem to have harnessed a lifeforce from deep below the ground somewhere in the root system!


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Postby Stephen1 » Mon Aug 02, 2010 10:08 am

The actual experimental evidence on when the best time to coppice is, is actually not very clear. The reason it's traditionally done in the winter seems to have more to do with when farm / estate workers weren't engaged in other jobs that actually were season dependant - i.e. they didn't have any more pressing jobs.

Studies over the last 15 years suggest anytime of year other than the 6 (or so ) weeks when the sap is rising fastest in the spring are equally appropriate for coppicing.

(For cherry there is a reduced incidence of wilt on the coppice regrowth if the coppicing takes place in early summer -this is the exception though amongst our native trees of one time actually yielding better results, other than avoiding the early spring).

(Also coppicing in early spring when the sap is rising and the cambium is starting to divide (starting to 'grow' that years growth ring)is when the bark is least fimly attached to the sapwood and so less than perfect felling technique will lead to more bark tears - which is also why early spring is the best time of year for stripping bark i.e. lime bast to make woven seats etc.)


Always worth leaving some birch as 'sacrificial' trees to the grey squirrels. They preferentially strip birch, offering the trees you have decided you want some limited protection.

Also worth keeping some birch as the host of new phytophthora diseases don't trouble birch, and who knows what the next twenty years will hold? The more diversity of tree species you have the greater the buffer your woodland will have against unexpected novel tree diseases and unpredicatable climate change. Although the planet is getting hotter (human or natural reasons) our island may get wetter, cooler and windier or indeed hotter and drier - there are models in the scientific literature predicting practically anything! I think the best way to plan a robust woodland against all these changing situations (disease/climate) is through maintaining the greatest diversity of appropriate tree species you can. That's what I try and do anyway!


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Postby Rich » Mon Aug 02, 2010 11:08 am

Hi Stephen,

That's very interesting, I had heard that most trees could be copppiced at anytime, but did not know that was the reason that we did it in winter. I guess trees and brash are a lot lighter and easier to handle in the winter too.


I agree with your sentiments about leaving as many species as possible, in this cant I've left at least one of each representative. Although I'm sure the birch does attract the attention of squirrels, I think the horbeam seems to fair worst. I'm currently processing some quite old specimens and you can see in the scars left in the wood go back many years.


Does anyone know how long we've had such a problem with squirrels, it would be interesting to corrulate if the start of these scars in the ring count coincide with the time of the squirrel population explosion.


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Postby Stephen1 » Mon Aug 02, 2010 12:58 pm

Hi Rich


Sorry I had it in mind yours was mainly Sweet chestnut. (Which of course squirrels do go for as well, but have a preferrence for birch over S.C., S.C. produces callous wood much more quickly than other trees and typically very successfully heals wounds- though these healed wounds are subsequently a favoured site for further squirrel attentions!)


Beech and hornbeam are of course major targets as well - sorry about my confusion over what you were working with.


Grey Squirrels were introduced in late Victorian times but have really only been a severe problem since the 1940s in most areas. (the stripping isn't feeding as used to be thought, it's an antagonistic territorial behaviour- two squirrels meet interact to identify dominance and then when they sepearate they ti some territorial marking i.e. stripping - they have no significant natural predators here, and so end up living at such high densities in some years that they are encountering other squirrels very frequently and so doing lots of stripping damage!)

Trees respond to squirrel bark stripping (if the stripping hasn't gone all the way around the stem) by producing callous wood to physically heal the damage, but also by producing chemicals that are moved into the exposed sapwood, these contain anti-fungal and antibacterial agents.

It's interesting (well if like me you're a tree nerd it's interesting!) that squirrel wounds tend to heal better than physical wounds made in other ways. The squirrels strip the bark, and usually the dividing/growing layer of cells called the cambial meristem, but do very little damage to the sapwood that they expose. This sapwood is left intact and fully functioning - so that the movement of protective chemicals into that sapwood is very efficent. Most squirrel wounds (obviously not if it's completly round the stem) heal very well. The timber will usually have been damaged in terms of its potential value in the future, but the tree itself often survives and grows very well if it isn't in too much shade. (this doesn't apply to birch or rowen)


You probably find cutting crossections through healed hornbeam that there is very little rot in the rings below each healed bit of squirrel damage? Where you cut a ring through healed damage at the base of a tree that has been damaged by timber extraction machinary etc. (and where the sapwood has been damaged beneath the bark) you would find that often there is significantly more and deeper rot/discoluration to the growth rings below any healed wounds.


Squirrels can change the relative proportions of broad leaved species over time in mixed woodlands - In our woods they give hornbeam,lime and sweet chestnut the advantage (which heal very well) over birch (which is less able to prevent the exposed wood from rotting by natural chemical means before the callousing physically heals and seals the wound, and when the wood beneath is weakend by decay the top of the tree blows out in the wind). The birch grows again from the point below this damage but is reduced in height compared to its neighbours so it then gets less light than they do and so is rapidly outcompeted by them as their canopies close above it.


One of the best studies of this is Peterken's work in Lady Park wood where squrrels have given ash a competitive advantage over beech - the beech are rarely killed but once they're topped by the ash their chances of becoming a dominant canopy tree are very limited.


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Postby Rich » Tue Aug 03, 2010 5:49 am

Hi Stephen,

Thanks for the detailed response. I will try and work out the age of the oldest hornbeam and see if the scarring corresponds. I'm thinking that the whole wood at one time may have been hornbeam as it is part of the high weald iron industry, plenty of charcoal platforms and bloomeries, but hardly managed at all the last 50 years as far as I know.

Have started controlling the squirrels so only got to keep that up for another 40 years to make sure future coppicers dont' see the same scarring!


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Postby Twybill » Tue Aug 03, 2010 7:10 pm

Birch is light demanding and Hazel can tolerate moderate shade. I would have thought that the Birch would help draw up the Hazel into the desired straight sticks. Just cut the Birch at a few feet above ground and the Hazel will rapidly overtop and shade it out.


Keep squirrels at bay by letting the brambles grow in between the stools. They don't like it as they prefer open ground where they cannot be suprised by predators.


Do the same with your woodland by having the standards/pollards well apart so the squirrels cannot jump from tree to tree and let the in-between go jungle like. The squirrels will stay away.


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Postby Stephen1 » Wed Aug 04, 2010 9:21 am

Twybill wrote;


"Keep squirrels at bay by letting the brambles grow in between the stools. They don't like it as they prefer open ground where they cannot be suprised by predators.


Do the same with your woodland by having the standards/pollards well apart so the squirrels cannot jump from tree to tree and let the in-between go jungle like. The squirrels will stay away."


Yes I agree in theory that would offer protection to the trees away from the edge of your proposed management style!

But how far apart would these trees have to be? Squirrels can jump a fair distance from the canopy of one tree to another - certainly a 5m / 15ft gap would be no obstacle for them - and with mature tall trees they could easily jump even further. Then there is the size of the spread of the canopy of mature widely spread trees to add? What would the growth form of these widely spread trees be?

What would the effect be on the groundflora of the wood other than the ubiquitous bramble? The wide spacing of the trees would initially allow plenty of light to the woodland floor which is great for a small proportion of the showiest native groundflora, but this has to be part of a cycle of gap creation and canopy closure (either natural at a small scale, following a canopy tree dying, or coppicing/selective felling)otherwise plants like bramble will smother everything else in time!


I think you'd be squirrel problem free if the trees were at 15m+ centres (i.e. very few trees to the acre), you'd have no problems with vandals, but you'd have no access and no specialist woodland groundflora and all that comes with that. I imagine it would be more akin to Parkland but with brambles instead of grass?


I'm as fed up with squirrels as the next person, but I don't think I'd want to sacrifice all you suggest to escape the problems they present?


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Postby Rich » Wed Aug 04, 2010 5:21 pm

...and with mature tall trees they could easily jump even further.


And given enough time they would also evolve wings, infact I think they probably already have somewhere!


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