Halo Pollarding.

 Halo Pollarding and Thinning.

Almost all quality timber production involves planting many more trees than are intended for the final crop. This gives very much more choice and as most timber is grown for several decades there is plenty of opportunity for reducing the number of trees particularly for removing inferior stems. This process is known as thinning. Commercial  management usually involves removing whole rows, known as Line Thinning. This was an uneconomic stage in the last quarter of the 20th century, as it was costly and the thinnings had little value, resulting in under managed stands. The rise of the wood fuel market has partly changed this but rising planting and labour costs have prevented its systematic reintroduction. 

Oak trees grown in a park try to be as wide as they are tall. This does not make for valuable long lengths of timber. To persuade the trees to grow taller and straight Oaks are often planted with other trees which shade the sides of the Oaks and encourage them to grow straight up. These other trees often conifers are known as nurse trees.  The conifers are then steadily removed, or thinned, as they get above  oaks by which time the Oaks have a predominately straight stem and no or few low branches as the trunks have received very little light. Less well grown Oaks from a row can also be cut down. Only about 30 Oak trees per acre are required for maximum quality yield after 120-150+ years.

Timber Quality Oaks from The Sotterley Estate web site.

A thinning method developed on the continent relies on halo thinning. Here the best oak trees are selected after only say 20 years and the trees which are touching their crowns are removed. Side branches may also be removed. The crowns get the maximum amount of light, but there are sufficient trees to stop side light from encouraging epicormic growth, (side branches) from the lower trunk. The method is described in "Oak: fine timber in 100 years" by Jean Lemaire, translated by Bede Howell. It is known as halo thinning.

I had initially decided not to plant Oak. I did want to see some final product and it seemed every small wood planted was being done with oak and an ancient woodland was the ideal. As I learnt more about woods I realised this would not produce timber trees. 

I had heard Bede Howell talking about halo thinning, and thought that the surrounding trees did not need removing completely. Only the parts that were competing with the Oak's crown.

Oaks in the foreground with a row of taller birch behind which are to be topped.

I had planted local oak seedlings at either end of Cairn wood in areas that it would be impractical to subsoil. These had grown quite well, I thought. Having given up, temporarily as it turned out, on Eucalypts I planted Oaks with fast growing mainly broadleaf trees. The idea being that the trees could have their tops cut off when they grew above the Oaks. Planting was carried out in the very cold winter of 2010/11. I had assumed that there would be a telescopic chain saw with a swivel head  that would enable a horizontal cut. This is not the case and in 2021/22 I started selectively removing the tops of Alder and Silver Birch with an angled, often messy, cut with a telescopic battery pole saw. If rot gets in at the top that is not a huge worry as the nurse trees are effectively sacrificial. The tops can make chip or fuel logs, the stems would make low quality logs. They would however keep the Oak trunks clean, epicormic free.

The oak on the left is the same oak as on the left in the previous photo. The photograph is from a bit further back and shows another good oak on the right hand side. These two trees are likely to be "final crop trees. The spacing being about right to give efficient crown size to both trees. The two two oaks between them would be cut down to allow that.

I had thought that this  idea was original, then I visited Norbury Park. Here Professor Jo Bradwell was doing the same, on a somewhat larger scale. He was also applying the idea to other Species. This gives me some confidence that I am not being silly. Norbury Park have a motorised telescopic pair of shears for removing the tops of the trees. (Gadget Envy). I am also doing something similar with potential timber trees at Pit Wood with cherry, Robinia and Sweet Chestnut in a less systematic way.

Professor Bradwell has referred to this as Halo Pollarding. He has used the term in print. (Norbury Park, An Estate Tackling Climate change 2022, RFS Journal July 2022 ) I have followed his lead though I think Halo Topping is a more accurate term.

A row of Birch which have been pollarded to favour the row of oaks on the right. The removal of the tops will also help the Western red cedars on the left. The cedars will be left while they do not interfere with the oaks, and will form a back up crop if there are not sufficient quality Oaks. 

This is a labour intensive way of managing. It is unlikely to be taken up commercially. The way this halo pollarding preserves standing timber promoting carbon sequestration and biodiversity means it might be an option for conservation driven woodlands to produce quality timber. Though grey squirrels and new pests and diseases make oak timber a less attractive commercial proposition, and provide wildlife woodlands with a dilemma. 

 

Drought Recovery Autumn.

 Drought Recovery Autumn.

The peak of the heat was in mid-July 2022, the drought extended until the end of August. From September there was sufficient rain to keep trees growing. October and November have seen a continuous series of weather fronts crossing the country and now November the 19th the ditch is full within a couple of inches of the top at the lowest point in the triangular field. There has had not been a ground frost in Sutton until the 22nd Nov.). By mid-November the native Oaks had started losing their leaves and most Cherry, Red Oak and Robinia had dropped. The greenest leaves are on the Sweet Chestnuts. Particularly those that were had sprouted since the drought or high temperatures, though there are not that many of them. see Drought

The same Rowan tree on the 20th July, the day after the record high temperatures, and on 19th. Nov 2022. The wilted leaves on the sweet chestnut turned brown and can be seen in the Nov. picture both trees had no green leaves at the end of July but grew new leaves once rain returned.

The image on the left shows reflushing from the trunk and probably dead branches. On the right there is similar greening from the trunk but only on the North side. The bark that was exposed to the sun on the south side looks necrotic. 

The browning was as much due to scorching as to drought. The worst affected trees were those on the southern edge. Most trees have subsequently produced green leaves, mainly from the trunks or close to them suggesting peripheral twig death.

Dead leaves in the crown of an E. gunnii on the left, epicormic shoots from the trunk on the right.
 

A Taiwania which appeared to die
in the drought showing epicormic
regrowth. Unusual in a conifer.

Most Eucalypts were not severely affected by the hot weather. One E. gunnii  in the area of worst affected Sweet Chestnuts had a crown of dead leaves in August. By the middle of November epicormic shoots were appearing all the way up the trunk. The tree is fuel log size and should be felled if the crown has failed, which is suggested by the amount of epicormic growth. The tree may continue growing well but growth will be into thin lateral branches. If pollarded a few verticals may dominate. The Sweet Chestnut will be reviewed after the spring flush, those without leaders will be coppiced. I may take the opportunity to coppice some of the poorly shaped Sweet Chestnuts as well. They are in amongst pole stage trees and may struggle for light.