Thursday, 28 March 2013

Cricket bat willows

I think I've found some cricket bat willows on the far side of the River Medway to the South of the parish boundary. There seems to be a short "almost" avenue (although the tree to the front of the group on the left hand side is actually an oak I think). The trees to the right are what I think to be genuine Cricket Bat Willows, usually referred to as Salix alba L. var. caerulea (Sm.) Sm. but also known as the cultivar 'Caerulea', which is much more upright, with branches soaring upwards at an angle of between about 20 to 40 degrees (narrower than the type) from the more or less vertical trunk (although this particular one has been cleft into two, and would certainly be useless for bat manufacture). I should be more sure of the trees' exact identity when I see the larger-than-type leaves and the green catkins in the later spring. One of the main reasons I'm considering these to be var. caerulea is the reddish-purple colour to the twigs underneath the grey pubescence, as stated in the Collins Tree Guide, and described as purple in Mitchell, although this isn't mentioned as a taxonomic feature in any of the more narrowly botanical books. Mitchell also suggests that the twigs are very slender. 

The characteristics of the cultivar according to the more botanical books are the upright branching habitat (narrower than var. alba, and giving rise to a conic (or pyramidal) crown, the larger and somewhat broader leaves (say 10 - 11 cm. long, 1.5 - 2 cm. wide, as opposed to 5 - 10 (- 12) cm. long, 0.5 - 1.5 cm. wide) that lose their hairs before maturity, particularly notably on their lower side where they are retained on var. alba (both types lose their upperside hairs relatively quickly, but var. alba remains silvery-hairy on the undersides), the apparently shorter bracts than var. vitellina (less than half of, as opposed to approximately equal to, the carpel length) but broader than the roughly equally short but pointy bracts of var. alba, and additionally it appears that the "outer" bark forms later than var. alba.   The leaves tend to be a blue-green colour.

It has apparently also be grown in Argentina as a timber tree in Argentina under the name "Sauce Alamo" (although this means Willow Poplar in Spanish?) - said to be grown on as much as 40,000 hectares in 1956, although I am unconvinced of this report (Poplars and Willows: In wood production and land use, from the International Poplar Commission) until I can find any confirmatory evidence. The tree does grow wild or perhaps naturalised in England, so from that point of view it could be regarded as a properly wild variety, however much planted, and this view is perhaps helped by the existence of the occasional male tree.

Here is a close-up of some more of the trees on the right, ones with straighter trunks. You can start to get an idea of the ruggedly furrowed bark on the trunks, even at this distance. They are in a fairly typical "willow" environment, with the trees' roots half in and out of the roadside ditch.

The nomenclature of the plant itself is a little bit confused. The name quoted above is derived from the fact that Sir J. E. Smith (abbreviated to Sm.) first named the tree as a separate species, Salix caerulea, in 1812 (English Botany, 34 t:2431)  but in the end changed his mind about its level of distinctiveness and renamed it himself as only a variety, Salix alba var. caerulea

Mitchell's reprinted book has it as coerulea, which is perhaps an older spelling, maybe going back to the 1800s. This therefore leaves it open as to which is the correct spelling, but I'll follow Meikle and the majority of the current writers, and use var. caerulea. Mitchell has also transposed in this text the reference to var. coerulea away from below the other varieties of Salix alba to below Salix 'chrysocoma' the weeping willow, so the text layout at least is a bit suspect.

var. caerulea is quite possibly a hybrid between var. alba and var. fragilis, but no-one really knows. Evidence is the intermediate size of the leaves, the variability of the trees, and the (hybrid) vigour of the trees' growth. However these particular trees at Hartlake don't look too vigorous - the maximum size of trees is said by some to be about 33m, or 100 foot high!

The tree is usually only found in its female form in England, but males do occur, finally conclusively demonstrated when several were found by Burtt Davy and Day, amongst others.  The wood of the male tree is inferior for bat manufacture, so it isn't deliberately planted commercially for bats. There are however various male clones - probably of var. alba - 'Liempde' (this one at least is susceptible to watermark disease), 'Belders' and 'Lievolde' that do appear to be grown for timber and as a street tree in Holland.

This is a closer shot of the bark at about chest height, which is described for Salix alba in the Collins Tree Guide as "dark grey; rugged, criss-crossing ridges". It sort of seems to fit, although any decision on these colours can be a real snare and delusion. In fact this bark looks to me in close-up perhaps to be a mid-brown, but largely covered in grey lichen! If so, my ID here may be at error. However good old Clapham, Tutin and Warburg have the description of the species' bark just as "greyish, not peeling, fissured, the ridges forming a closed network". Wikipedia has the bark as "greyish-brown", even better, drawn from R. D. Meikle's handbook on Willows and Poplars for the BSBI.

Making cricket bats out of the trees is not so easy, and I doubt any of these trees would be much use. Here is a clear description of how it is done.

And here is more information on grading clefts for bat production, including the vexed issue of grain number - The trees for commercial bat production have to be grown carefully in a controlled plantation, managed very intensively and with any subshoots rubbed out (upwards) of the main trunk at a very early stage and are harvested at between 15 and 30 years old. A small midge larva that feeds on/underneath the bark can cause small flecks in the wood of the bat.

Clearly at least one thing has gone wrong with this particular trunk below, resulting in a whole clump of stems springing out of what might be some small bolls on the left hand side, and a definite kink in the trunk. These clefts  won't be any good for making cricket bats! Commercially produced trees have to have any small side-shoots growing out from the straight trunk rubbed out - at a very early stage!

It's interesting to make the link between the trees and the finished product, as Milton Keynes Parks Trust have done here:

In fact almost all trees commercially produced in England are from East Anglia, the majority of which are produced by J. S. Wrights of Great Leighs, Essex, who have a fascinating website: Most of the clefts are I think exported to the Indian subcontinent where they are turned into bats - only a very small specialist industry of bat manufacture actually remains within the UK as seen in this video - Presumably then the finished bats are sent all over the world, including being returned to England for sale in local shops, such as our own local Kent Cricket Direct in Southborough.

Various willows, including var. caerulea are affected by the bacterial "watermark disease" Brennera (Erwinia) salicis and here is the Tree Advice Trust's leaflet on the problem:

Going back to the trees growing along the road to Hartlake, the young shoots are reddish-purple-brown, particularly on their tops, but can look greyish in some lights - due to small short hairs covering the surface? Two year old stems are however an olivaceous colour, clearly contrasting with the browner younger shoots.

Willows are also probably very useful for wildlife - here you can see what are probably beetle exit holes in the heartwood, exposed in this knotty wound. The surrounding lichens are also quite interesting!

This particular tree is probably also quite useful for wildlife:

And I think I may not be the only person (not surprisingly, they are SO interesting) blogging about willows!

Saturday, 8 December 2012

Monoliths - in the tree sense!

These oak trees along the College main drive were under threat of complete removal, but "woodsman, spare that tree!" and they have been left as the amazing habitat that they are, as single trunks or monoliths. The idea is that they continue to stand for many. many years to come, improving the habitat possibilities of the grounds immensely, providing some visual interest (a little controversially perhaps, but the more of these there are, the more people get used to them, and the more acceptable they become), and of course being used as an educational tool. It would be wonderful to just take a group of landscapers and garden designers along the drive and see what you can get out of looking at all the trees - perhaps assessing the landscape value, perhaps the biodiversity interest.

The complex structure of holes and crevices looks very suitable for bat resting or roosting in the summer or winter if the level of disturbance is not too off-putting.

Friday, 30 November 2012

The wonderful oaks along the college drive!

This is one of the younger oak trees along the drive, towards Garrard House, maybe over fifty years old, vigorous and in good health.

This tree in the picture below is quite a bit older, middle-aged perhaps, and has not had an easy time of it. It has now been greatly reduced to provide greater safety to passers-by. This should allow it to be retained for many more years to come, although probably not all the way through its natural lifespan.

This next picture is of one of the best trees in the whole parish, an old giant of an oak that sits just outside Garrard House, and must be well over 100 years old.

This lovely oak opposite the staff car-park entrance has been heavily pruned in the past. The large boll on the left shows several apparently flush pruning cuts of what appears to be secondary branching that have no signs of later callusing over, although they are now very much hidden in the surface of the main trunk.

This picture below is an example of a very large branch having been removed. The tree made valiant efforts to heal itself, and there is a good roll of callus in a nicely circular surround over the wound. The decay in the heartwood in the centre however was pretty inevitable when making such a large wound, and removing such a large branch, and really the only way to avoid this is to think fifty years or so ahead, and do your formative pruning while the branch is still small!

The surface of the decaying heartwood looks as though it has been covered with black wound paint - the wood below looks much paler - now very much out of favour, although it was very much in vogue up to about 15 years ago. It is now thought to do more harm than good.

It is however interesting to compare the picture above with the one below, a large wound, which does not show any sign of wound paint applied, that has healed pretty well on the Garrard House oak - although not too many conclusions should be drawn as there are so many factors involved.

More Scots Pine further up the drive

This picture, taken looking very high up towards the top of one of the Scots Pine trees along the upper part of the drive, shows a typical "rip-out" scar of a dropped branch from surprisingly high up in the canopy. Its such a shame that such a high branch has been lost and its a bit difficult to imagine how it happened!

I had never noticed this following structural difference before, only the obvious colour change as you go up the trunk! This picture shows the often typical reddish scaly bark found higher up the trunks of the trees, as opposed to the scaly fissured bark found lower down the trunk (lower picture).

In the picture above of the bark at chest height, you also have the green algae growing on the North side, on the left. On the right hand side you can see more of the proper colour of the scales, but the bark is never as smooth or as orange as the smooth scales near the top of the tree, and the bark is more a mid-brown at its warmest.

The Scots Pine trees further along the drive do look subtly different, from the ones nearer the A26. They seem to me to far wiggly in their trunks and branches. Here are some wiggly branches high up in the canopy;

and here are some bendy tips to the trunks - very odd!

Overall most of the trees higher up the drive look a bit bendy and wiggly as in the picture below, if you look closely at the way the branches have developed.

and the trunk of the young one on the right in the picture below just doesn't seem to know what on earth it is doing!

This last picture (below) shows what looks like woodpecker damage high up on an apparently healthy branch. I am not sure what other explanation there could be for this (apart from climber damage), and the branch does overhang a target - the college main drive - so it could be worth keeping an eye on. Some of the branch has been apparently quite deeply pecked into, and some other areas of surface bark apparently levered up. It all fits with a woodpecker trying to get at insects inside the branch, but there is no sign of ill-health in the branch foliage, so maybe it will remain a mystery!

Thursday, 29 November 2012

Scots Pine along the College Drive on the first real day of winter

I spent a chilly hour this afternoon walking Monty around the front of the college campus and took a few photos.

The Scots Pines along the main college drive are a real structural and heritage feature of the college environment, and the older ones are absolutely fantastic trees, certainly well over 50 years old, some possibly much older. Many of them are suffering from the damage and disease implicit on this site where the trees and landscape are not really heavily prioritised by the senior management (despite the best efforts of the Head Gardener) and are very unlikely to achieve their potential lifespan of anything up to 550 plus years - one of the victims is on the left of this line, "cut off in its prime" at about 8 metres, with only one significant branch left.

These are on the way out long before their time and are gradually being replaced by younger trees within the row. These are about 20 - 30 years old and still overall roughly triangular in outline shape, as most young pines are. You can see their much thinner trunks in among the thicker trunks of the older trees.

These pines below have been seriously damaged by the recent deep trenching within their root protection areas to lay cables between the light standards, although the damage will only gradually become apparent in slower growth, loss of branches and increased disease attack. To be fair, the roots may not have been expected because of the intervening ditch (which the roots actually spread underneath following the ground contours faithfully) but we need to learn how to protect our trees from this sort of carelessness.

The picture below is the crown of one of the older pines, again with many missing branches removed from up its trunk. This is partly natural due to the tree's age, and the resulting expected sub-crown loss, but still, it has occurred earlier in the tree's life than it should have. The tall narrow crown forms may be partly genetic (one of the dozen plus genetic forms Scots Pines are known to have) or partly environmental (due to close planting in this avenue). The trees are likely to be European rather than Scottish in their primary genetic origin, as so many of the Scots Pine grown in England appear to be, seed probably brought over from the continent sometime in the last few hundred years to grow these trees or their parents.

Conifers were marked along this driveway on the 1890s, 1900s, 1930s and 1960s OS maps, and the pine trees still growing there are a historical marker of the local landscape going back in a continuous thread to the times when Bourne Grange (now renamed as Garrad House) was a substantial mid-Victorian private residence in its own grounds on this site.

The bark of the Scots Pine is wonderful multi-coloured layered flakes - usually with a more orange shading higher up the trunk that is more developed in this species than almost any other pine.

The trees are well furnished with this year's young female cones newly closed having received pollen in the spring of 2012, last year's female cones all sealed up and armoured with their slowly developing seeds inside them, and the two year old female cones now fully opened up (they continue to open and close according to moisture levels) having released most of the matured seeds or "pine nuts":

More on Scots Pine from the Trees for Life Project in the Scottish Highlands