Sunday, 28 February 2016

Why do beech trees lose their limbs

One of our largest beech trees,  probably the largest in Old Copse, with a girth of 6 metres (19ft 8ins) measured at a height of 1.5 metres, recently dropped an enormous limb, 25 metres (82 feet) long. Lucky we weren't around when it happened.  We wondered why the limb had broken off when it did and  initially thought that it might have been caused by recent strong winds, but reading up on the subject, found that wind is highly unlikely to have caused the limb  to part company with the tree. In the case of this particular beech, it might  have been due to a weakness at the point where the branch joined the trunk, where fungus, evidence of rot, can be seen. Another beech, younger and smaller than our giant, and about 4 metres away, also dropped a limb, though there was no sign of rot.

Below is a blog post (Ashley Peace on the subject of why beech trees make a habit of losing their branches. The  ancient beech tree in the photo is near Burwash in East Sussex. It is surprisingly, smaller than 'our' beech, which undoubtedley is younger than the Burwash tree, which is estimated at being from 200 - 250 years old. It certainly looks a lot older, and very gnarled. I expect, though,  that trees, like people, shrink a bit as they become aged. 
beech near Burwash, E. Sussex (Tim Symonds)

'The beech in the above photo is near Burwash, East Sussex. It displays clearly how the beech can drop its branches if need be. This one is in clay soil, on a steep-ish slope, about thirty metres above a tiny brook. The Woodland Trust guessed it must be between 200 and 250 years old. It is 220 inches in girth at 5 feet.

 So, why would a tree want to lose its branches? It might seem like a ridiculous thing to do, considering the time and effort invested in growing them. Yet many biotic and abiotic stresses (e.g. water  shortage or disease) may cause a tree to shed branches. However, given the size of this specimen, it is likely that simple old age is the causal factor - senescence. I believe the following article describes the whys and wherefores of geriatric branch shedding particularly well. I will reproduce it here in its entirety, The author is Peter Thomas (a lecturer in environmental science at Keele University (UK)), and the article originally appeared in the May 2002 edition of Natural History magazine.' (Ashley Peace)

To live long, a tree must stay small. 

Old age is not the problem for plants that it is for animals. Being modular, plants can grow new limbs when old ones die off. More crucial to the longevity of a tree is its size. A tree reaches a stage when it cannot get taller, owing mainly to the difficulties of bringing water up from the roots, and when its side branches cannot grow longer, because they are too expensive to support. So the number of leaves a tree holds becomes more or less fixed, and this means that the tree's ability to produce food--the sugar made in leaves by photosynthesis--also levels off. 

Yet each year the tree adds a new layer of wood under the bark, and the amount of wood needed to coat the whole tree increases, just as, in a set of Russian dolls, each new doll on the outside has to be bigger. As the tree grows, the amount of food needed for running it rises. The tree resembles a bank account whose income (sugary food) is fixed but whose outgo (respiration and new wood) keeps mounting. The tree compensates for a time by producing narrower and narrower rings, but there comes a point when a ring cannot get any narrower. Something has to give, usually the water-deprived top most branches. The result is a stag-headed tree, so named for the antlerlike dead branches sticking out of the top. A downward spiral begins: the loss of branches means fewer leaves, and fewer leaves means less new wood. 

But many trees can slow the process. Some have buds in the trunk that sprout new branches. These may hold enough leaves to make up for those lost higher up, so the tree can keep the leaf area constant while cutting out the expensive-to-maintain upper trunk and its big branches. 

Although these new trunk branches are fairly short-lived (a hundred years in oak, sixty years in hornbeam and beech, and less in birch and willow), an oak with plentiful trunk buds can stave off death for centuries. As the old saying goes: "Oak takes 300 years to grow, 300 years it stays, 300 years it takes to decline." Perhaps we should think of a stag-headed oak as merely entering middle age and, like many humans, just going a little bald on top. 

A tree has no fixed life span. To live long, it must stay small. One way to do this is to grow slowly. Bristlecone pines are the supreme example: they live on poor soil in a dry, cold environment with a short growing season. One bristlecone in the American Southwest has been documented at three feet tall, less than three inches in diameter, and 700 years old! The other way to stay small and live long is, paradoxically, to be cut down repeatedly. (This strategy, of course, will work only for trees capable of regrowing when cut.) The ash Fraxinus excelsior normally lives for 250 years, yet Suffolk, England, hosts a coppiced ash with a stump almost seventeen feet in diameter. It is at least a thousand years old. 

A tree's bank balance is also influenced by savings in the form of food reserves. As a tree gets bigger, however, it has less food left over. At the same time, the larder--the sapwood--gets smaller. Eventually, infections penetrate inner structures, and storage capacity is lost behind a barrier zone, a layer of new cells produced in the inner bark to seal off infected wood. The living part of the tree is walled into a thinner and thinner space under the bark. Part of the tree dies. New branches on the trunk can still save its life, but a large old tree is not good at producing new shoots, perhaps because it is running out of stored buds or because they are trapped behind thick bark. New sprouts on weak trees often die just when people think the tree is going to live. This may be because the barrier zone is missing or because there are too few reserves left for the tree to grow a strip of tissue from the new branch down to the roots. Either way, disease easily overtakes the tree, and the branch withers away. At this point, the tired old tree bows out gracefully. 

Seen in the Wood Today: On the pond we were pleased to have a visit from a Grebe, a welcome sign of Spring. We don't know if  he/she? is new to the pond, or just visiting from the Hammerpond nearby. A pair of Grebes live in the reeds over on the Hammerpond, but we don't know how successful they've been in raising a brood. 

Tuesday, 9 February 2016

Some thoughts on 'What are 'small' woodlands for'?

Woodland flower bed with antirrhinums and lavender.
The post that started the discussion.
A discussion last year on the SWOG (Small Woodland Owners Group)Facebook page got us thinking about what activities are part of managing woodland for conservation and biodiversity. A SWOG member was upset that many of the group appeared to be interested mainly in bushcraft schools, timber production, and building construction, whereas their prime aim should be the creation of a small nature reserve. He was particularly upset by another SWOG member who had posted a photo of his flower bed  fronted by a homemade hurdle fence, and backed by planted willow. It does look like something you might see in a garden rather than in a woodland . He was concerned about the introduction of non-native species into woodland, and the risk of non-natives taking over native plants, e.g. as is happening with native bluebells being ousted by 'Spanish' bluebells. In fact he frowned upon doing anything much in woodland, except say, to remove alien species such as rhododendron, and perhaps visiting for a little 'wild' camping, but apart from that, leaving it strictly alone.

The law  allows  a temporary caravan for the purposes of forestry,
though it doesn't look as if this one is moving at any time soon. 
You can camp in your woodland for up to 28 days a year
Making a woodland playground for children: good idea or not? 

But would this minimal intervention approach produce a 'nature reserve'. And what exactly is a 'nature reserve ' anyway? Will one just happen by not doing anything? Unlikely. Our current woodlands are the product of centuries of human intervention: pollarding, collecting firewood, grazing animals. And are woodland 'nature reserves' what is wanted or needed?

There followed a short Facebook discussion on what is ok to do in your own small patch of private woodland. Many people want to use theirs primarily for recreation and leisure, camping, and social get togethers, and a 'playground' for encouraging children to learn about, and enjoy the environment. Others are more interested in their gaming rights, and want to shoot rabbits, squirrels and deer, controlling all animals which could be seen to be detrimental to the regeneration of woodland habitat. Others are into machinery, though that begs the question of how much of that is really needed for these small bits of woodland.

But, as is evident from many of the postings on the site,  the majority of owners want to manage their woodland whether formally (via an approved plan) or informally. There isn't much evidence that owners intend to leave it alone to do what it wants. Traditionally woods were managed for both timber and for the useful products of the underwood - hazel poles and willow for hurdles. Regular coppicing let in light, allowing species to flourish, and increasing diversity. Changing economies mean that there is little use for coppice products in the 21st century, and the demise of traditional management has led to the overstood condition of many English woods. We know what happens to completely un - managed woodland - it soon becomes increasingly dark, dominant species take over, brambles and bracken flourish on the ground layer to the detriment of other light-loving plants - soon it becomes impenetrable. Nobody will visit it, nobody will take an interest.

The poster who started off the SWOG discussion seemed to be most exercised about the more commercial aspects of owning woodland, feeling that such activity is bad for the woodland environment. I don't think he needs to worry. Small woodlands are very unlikely to turn a profit. I've never heard of 'so and so' the charcoal burning, firewood selling, pole turning millionaire. It's entirely the wrong business, with perhaps the exception being those agencies mentioned below who sell off woodlands in tiny parcels. For the owner of a small patch, it might be possible to make a little cash, and obtain some public grant money for some equipment, and perhaps some deer protection etc, but it will never cover the cost of  labour. Though I don't think this bothers most owners. Even for PAWS (plantation on an ancient woodland site) owners like ourselves, 60 years after these were planted, the thinning operation costs almost outweigh any income from the timber.

Woodland bee-keeping
During the last 20 years or so, interest has grown, exacerbated by David Cameron's threat to sell off public woodland into private hands.This focused people's attention. As interest grew, a new business opportunity was identified. The company that hosts the SWOG facebook page set about buying up large-ish woodlands, tidying them up, putting in gates and access tracks, and dividing them into very small Lots of around 4 - 8 acres. These are then marketed at a premium price,. Many people are encouraged to buy their own small piece of woodland, albeit with neighbours, each with their own idea of how their plot should be managed, or not. No wonder then, that one owner wanting to put a nice little garden in his wood might then disapprove of his neighbour doing nothing, Where there is no cohesive management of the whole woodland, this seems likely to happen. 

This isn't necessarily a complete pessimistic outlook. Small woods are gradually finding their place, No longer an essential part of the village economy, small woods have become 'hobby woods' - places to enjoy and connect to the outdoors. What is clear is just how much pleasure they give their owners. By getting to know a piece of land through the seasons, closely observing the changes, owners - and that includes us - can't help but be inspired to preserve and improve what we have. We may all argue about the best way of getting there, but we are all united by a love of woods and a desire to see them flourish. 

All the illustrations used in this post are borrowed from the SWOG Facebook site. 

Some extracted quotes from the SWOG facebook page:

'.While we're aiming for a balance between a modest sustainable income and a wildlife friendly approach, not every woodland owner is motivated by future revenue and value . Amenity, education, and wildlife protection  are enough objectives for many small wood owners, those are also very worthy pursuits. As has been said before there are many different owners, woods and approaches, there's room for a diversity of views'  

Watching wild-life
'Just a warning. I have been a forestry contractor for 20 years and many small woodland owners have grown great big useless trees and then after 20 or so years have realised that this great big useless tree is about to fall over and destroy 20 others. Then they ask how much it costs to take the tree down. It normally stops there and the 20 trees get destroyed. My question is what is the difference to the wildlife in growing a good timber tree to a poor one. My second question is where is your sustainability. My third question is bearing in mind that since the ice age British man has been growing timber in this country which has built the wildlife around it. Do you think that changing the way you manage your woodland changes the wildlife? and if so why are you not carrying on what has been done in this country for over 7000 years'
Charcoal production

Keeping the home fires burning
'We have a management plan agreed with the forestry commission for managing different parts in different ways. The new planting will be thinned when appropriate. We do not just leave it until it gets out of hand. However, pruning off the side branches reduces the cover for small birds and also reduces the chance some will rot to provide holes. This has all been agreed. Other areas will be turned into coppice, the willow on a shorter rotation. The end product is an ecosystem and the by product is a selection of poles, firewood, wood for turning and crafts, and the occasional timber tree and hopefully a good number of veterans too. We are carrying on exactly as has been done for thousands of years with sustainable coppice plus continuous cover. It has worked very well so far. 

Willow grows all over the local area including all through our ancient wood because of the soil. We are only following what grows naturally. We will not need a contractor to help us. We have done all the work ourselves and are both qualified with chainsaws although we get professionals in to do any climbing and pollarding. We have been accused of over managing our woods by others on here. It is a fine balance. For our own land and objectives we think we have got it right. '

'My own approach is to work towards mirroring the medieval continuous cover approach, where there was always a mixture of trees ages and species, rather than a purely commercial modern plantation approach.