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Sweet chestnut blight found in Britain

March 22, 2012

Gabriel Hemery

The fungus that wiped out 3.5 billion chestnut trees in the USA has been found for the first time in Britain. Chestnut blight, caused by the fungus Cryphonectria parasitica (C. parasitica), has been confirmed by Forest Research scientists on trees in two small orchards of European sweet chestnut (Castanea sativa). The trees were imported by an English tree nursery from the same grower in France. The sites in Warwickshire and East Sussex are the first findings in Britain. Until now, the English Channel had prevented its spread from mainland Europe.

The fungus infection is usually fatal to European sweet chestnut and its North American relative, Castanea dentata, although it appears to be less virulent in Europe than it is in America. It is believed to have first originated in Eastern Asia before being introduced to North America in the late 19th Century, where it has since devastated billions of trees in the East of the country (see The American Chestnut Foundation). It was first identified in Europe in 1938, in Italy, and has since spread to most parts of southern Europe where sweet chestnut is grown, and to parts of northern Europe.

Identifying chestnut blight

The most obvious symptoms of chestnut blight are wilting and die-back of tree shoots. Young trees with this infection normally die back to the root collar, and might re-sprout before becoming re-infected. Other symptoms, such as stem cankers and the presence of fruiting bodies can also occur.

What now?

The trees where the fungus were discovered had been imported into the UK for nut production. As I have written before (e.g. Climate Change and Global Trade), the import/export of trees is potentially the most significant factor in the spread of new tree pests and diseases. Case proven I think.  Let’s hope that FERA (Food & Environment Research Agency of the UK Government) is given adequate resources to tackle this very serious fungus. Afterall, sweet chestnut is a beautiful tree species in our forests and when coppiced, as it is in commonly in Kent (see Sweet Chestnut Coppice), it is one of the few forest systems that pays well and regularly.

Gabriel Hemery


Weekly photo challenge: mountains

August 9, 2011

Gabriel Hemery

Sunrise in the Cevennes
Sunrise in the Cevennes

Sunrise in the Cevennes, France. DMC-GF2, 120mm zoom (240mm 35mm equivalent), f11, 1.0 sec, ISO100, tripod.

Sunrise and valley mist in the Cevennes mountains of south east France.  The forests contain a large proportion of sweet chestnut (Castanea sativa) trees, alongside downy oak (Quercus pubescens) and various pines and spruces.

Gabriel Hemery

Sweet chestnut coppice

June 25, 2011

Gabriel Hemery

Maiden sweet chestnut and coppice
Maiden sweet chestnut and coppice

Maiden sweet chestnut tree and coppice in Kent. DMC-GF2, 14mm (28mm equiv), f7.1, HDR 5 shot composite (5x 2/3exp), ISO100, handheld.

This week I had the pleasure of visiting Kent – “England’s garden” – famous for its apple, cherry and cobnut growing.  It is also the centre of Britain’s sweet chestnut coppice industry.

Sweet chestnut (Castanea sativa) was introduced to Britain by the Romans some 2000 years ago.  Its attraction was the nutrious nuts produced every Autumn within the hedgehog-like prickly shells or cupules.  Sweet chestnut also produces some of the most durable of timbers, which is resistant to rot and very strong.  Its cleaves, or splits easily along the grain, which makes it a perfect wood for making pegs, stakes, or fencing.  The unrelated horse chestnut (Aesculus hippocastum) has nuts that are inedible and a wood which is virtually unusable, even for burning.

Sweet chestnut coppice

A working sweet chestnut woodland in Kent. In the foreground is a recently cut coppice cant, middle distance (left) is a stack of cut poles with maiden trees behind, distant right is a cant of 15 years old coppice. DMC-GF2, 14mm (28mm equiv), f7.1, HDR 5 shot composite (5x 2/3exp), ISO100, handheld.

Historical records from Canterbury Cathedral show that there were large areas of coppice grown in Kent by 1200.  The chestnut coppice industry expanded rapidly during the 19th Century to meet a growing demand for hop poles from the brewing industry.

Sweet chestnut coppice is grown on a 30 year cycle.  It is managed in felling coupes or ‘cants’ that are usually sold ‘standing’ (i.e. uncut) to coppice workers, whose experienced eyes allow them to quickly assess how many poles and stakes they can produce from a cut.

I visited Torry Hill Farm, run as a family business by John Leigh Pemberton.  The Pembertons have revived and transformed the industry in growing quality chestnut using efficient silviculture, backed by smart business know-how.  They provide FSC-certified chestnut products, ranging from pegs, cleft stakes, wired fencing, fencing stakes and rails, supplying wholesale across Britain and now exporting to France, Germany and even the USA.

Cleaving sweet chestnut

A skilled worker cleaving sweet chestnut at Torry Hill Farm. A froe is used to split or cleave the wood which is held in a cleaving brake.

Cleaving chestnut is a skilled job and Torry Hill Farm now employ some 15 workers in their Kent factory.  The stakes and rails are split or cleaved by hand using a froe.  The skill is in selecting the wood and being able to ‘read’ it, almost without thinking, knowing how to best produce the greatest number of quality stakes from a pole.

Sweet chestnut coppice cleft stakes and brash faggots

Sweet chestnut coppice cleft stakes and brash faggots

Torry Hill Farm produce carbon lean, natural and sustainable products that are growing in their popularity.  The wired chestnut fencing familiar on construction sites is now widely used for dune restoration projects and in zoos, while a 6′ (1.8m) high variant is becoming popular for deer fencing.  The small amount of waste is used to produce heat in the factory, and there is even a growing market for the brash (branch tops) which are bundled into ‘faggots’ and used to repair river banks.

I was inspired by the visit, particularly in how the combination of innovation, hard work, top quality silviculture and business know-how has built a profitable international business that was not dependent on Government hand-outs for woodland management.  If only other silvicultural regimes could be so productive.

Gabriel Hemery

How big will this tree grow?

June 15, 2011

Gabriel Hemery

Many people are interested in how big a tree’s crown will grow. It can be important in planning gardens, managing street trees, forest silviculture and in assessing the health of ancient trees.

Estimating tree height is very imprecise as it is dependent on so many different factors.  However, I wrote recently about the very good relationship statistically between a tree’s stem diameter and its crown diameter (read more).  I have received several requests for more information, and for this to be presented in a way that could be used by those who care for and manage trees.

So I have reworked the graph to produce a simple plot of tree crown diameter and stem diameter for the following nine species: ash (Fraxinus excelsior), beech (Fagus sylvatica), silver birch (Betula pendula), wild cherry (Prunus avium), sweet chestnut (Castanea sativa), oak (Quercus robur & Q. petraea) poplar (Populus spp.), sycamore (Acer pseudoplatanus) and common walnut (Juglans regia).

tree crown diameter and stem diameter graph

Tree crown diameter and stem diameter for nine broadleaved species. Click to enlarge.

Here is a simple summary of the same data in a table, presented in 0.10m stem diameter (dbh) increments.

crown diameter (m)
dbh (m) walnut ash oak sweet chestnut wild cherry beech sycamore silver birch poplar
0.10 4.47 2.65 2.50 3.86 3.30 2.52 2.48 2.58 2.71
0.20 6.23 4.54 4.28 4.93 4.84 4.10 4.37 4.19 4.60
0.30 7.99 6.43 6.05 5.99 6.38 5.67 6.26 5.81 6.50
0.40 9.75 8.32 7.82 7.06 7.92 7.24 8.15 7.43 8.39
0.50 11.51 10.21 9.59 8.13 9.46 8.82 10.04 9.05 10.29
0.60 13.27 12.10 11.36 9.19 11.00 10.39 11.93 10.67 12.18
0.70 15.03 13.99 13.14 10.26 12.54 11.96 13.82 12.29 14.08

The data for this work was collected from open grown trees.  Note therefore that trees grown in forest conditions, where they will have been affected by light levels and other competition factors, will not follow closely the data presented here.

I hope that this data may prove useful for those who are interested in scoring the condition of ancient trees, in planning tree avenues, and in garden planning or landscape architecture. Remember that the results presented here are based on peer-reviewed scientific work: if you want a reference for this work you can find it in my previous post on this subject (click here).  Let me know if you find a use for this data.

Gabriel Hemery

Estimating tree crown size

May 23, 2011

Gabriel Hemery

I co-authored an academic paper in 2005 that summarised research undertaken to explore the relationship between a tree’s stem diameter and its crown (or canopy) diameter 1.  Out of my 60 or so publications, it has been one of the most popular among forest scientists (e.g. Google Scholar citations).

It was fascinating to discover that statistically there was a very good relationship (scientists would refer to a correlation from a regression analysis) between stem diameter and crown diameter.  We decided to explore this further by calculating the ratio between the two, we called it the z ratio (= crown diameter ÷ stem diameter).  We then plotted this z ratio against stem size.  You can see the result on the graph below for nine common European broadleaved trees.

Tree crown and stem diameter ratio graph

Crown diameter: stem diameter relationship for nine broadleaved tree species. The z ratio (y axis) is crown diameter divided by stem diameter; the dbh (x axis) is stem diameter at breast height (measured at 1.3m). Click to enlarge graph

The graph highlights some very interesting growth patterns and difference between different species:

  • Common walnut (Juglans regia) has the largest crown diameter at any given stage in its stem size.  When a walnut stem is 15 cm in diameter its crown can be estimated to be 5m wide.  Foresters can use that knowledge to design walnut plantations: e.g. if they plant their walnut trees 5m apart, their crowns will not compete until their stem diameter is 15 cm (which will take about 15 years from planting in the UK).
  • Sweet chestnut (Castanea sativa), like walnut, has a very large crown while it is young (with a small stem size).  Unlike walnut however, as its stem size increases, the ratio with its crown diameter decreases rapidly to the point after 35cm in diameter, when it has the smallest crown diameter for any of the nine tree species assessed.
  • Sycamore (Acer pseudoplatanus) has the most consistent crown to stem ratio while it grows.

basal area per hectare (G, m2 ha-1)The data can be used to plan tree spacings and to calculate basal area.  For example: for walnut with a stem diameter of 0.60m, its crown diameter is 13.27m, and its z ratio is 22.12.   Using the equation (left) for estimating basal area per hectare (G, m2 ha-1) tells us that there would be 57 trees per hectare with a basal area of 16.1 m2 ha-1.

These findings can be used beyond tree spacings and calculating basal area; they can also be used to help in:

  • planning thinning regimes (how many trees to remove in a growing plantation and when)
  • planning stand density (how many trees to retain in a forest stand at any given size)
  • assisting in managing mixed conifer-broadleaved stands
  • estimating branchwood  and woodfuel volumes
  • maintaining free-growth silvicultural systems, and
  • in urban tree planning by arboriculturists and landscape gardeners (e.g. designing and managing tree avenues).

Gabriel Hemery


Reference

1 Hemery, G.E., Savill, P. & Pryor, S.N. (2005).  Applications of the crown diameter – stem diameter relationship for different species of broadleaved trees. Forest Ecology and Management 215, 285-294. View abstract

Tree honey

May 18, 2011

Gabriel Hemery

miel de chataignier

Miel de châtaignier from a recent foray to France

I love honey.  I also love France and visit whenever I’m able to, often returning home to Britain with several jars of local French honey.  The first time I came across Le Miel de châtaignier I was intrigued.  My dictionary told me that this was honey of the sweet chestnut (Castanea sativa).  But, surely, sweet chestnut is wind-pollinated so how was it possible that bees were collecting its pollen and the French apiculturers (beekeepers) were able to make sweet chestnut honey?

The literature tells us that sweet chestnuts are wind-pollinated but I’m not so sure that this is completely accurate.  As Peter Thomas explains in his excellent book (Trees:  their natural history p. 133), in reality there is a blurring between wind and insect-pollination in trees, with the pollen of all the major European wind-pollinated trees (ash, birch, hazel and oak) having been found on honey bees.

In the case of sweet chestnut it has sticky pollen, which you will notice if you brush your finger against a flower.  Its flowers are also sweet-smelling and always seem to attract a lot of insects.  Typically, wind-pollinated flowers do not have sticky pollen and do not smell sweet.  Furthermore, try tapping a sweet chestnut flower to see if a cloud of pollen is released as it is for wind-pollinated trees such as alder, hazel or walnut:- it is not.  So, in my view, sweet chestnut is most definitely insect-pollinated and perhaps almost exclusively.

Sweet chestnut honey is quite dark and strong-tasting, and not necessarily my favourite for spreading on bread or toast although it’s excellent in cooking.  Here’s a summary of the some of the popular, and less well-known, tree honey varieties.

Acacia

Acacia honey, made from Acacia spp. tree flowers, is remarkably clear and pure and is one of the most popular and sweetest of honey varieties.  Due to a high level of fructose it stays as a liquid (i.e. not crystallising) for a long time. Its low sugar content makes it the honey of choice for diabetics.  It has a neutral taste (unlike sweet chestnut honey!) making it a popular with children and suitable for sweetening drinks.

Lime

Lime honey is produced from the cream-coloured flowers of the lime  or basswood (Tilia spp.), having a light colour yet a strong taste.  Some say it has a ‘woody’ flavour and it is a popular honey for marinades and salad dressings.

Eucalyptus

Eucalyptus honey is a popular and widely-produced honey.  Given the large number of different Eucalyptus species, its honey differs widely in colour and taste.  Generally it has quite a herbal taste, with a hint of menthol, and may not be to everybody’s tastes (especially children).  It is said to be an effective cure for colds and headaches.

Leatherwood

Leatherwood honey is made from the flowers of Eucryphia lucida, a small tree native to Tasmania.  It has a unique floral yet spicy flavour and is considered a gourmet honey, being exported around the world.  It is excellent in cooking as it adds not only sweetness but a wonderful aroma to cakes and muffins, and to warm beverages.

Pine

This is a generic honey, similar to ‘forest honey’, and is a popular honey in Greece.  It has a strong smell and is not very sweet, having a rather bitter taste.  It is a little like Acacia honey in that it will remain a liquid for a long time.

Strawberry Tree

Strawberry Tree or arbutus  honey comes from the small tree Arbutus unedo native to the Mediterranean; where in Sardinia it is known as miele amaro (bitter honey).  As this suggests, it has a strong bitter flavour but it is appreciated by honey connoisseurs.

Sweet Chestnut

Sweet Chestnut honey is made from the flowers of Castanae sativa and has a strong aromatic flavour and a slightly bitter after taste. It is dark in colour and richly aromatic, some say pungent!  It is not very sweet and slightly bitter.

Tawari

Tawari honey is made from Ixerba brexioides native to New Zealand.  The honey is golden in colour and is said to have a butterscotch flavour that is very subtle.  It is prized in the kitchen for desserts, being a favourite on pancakes and ice cream.

Gabriel Hemery

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