Saturday, 1 December 2007

Christmas trees

It's December so a good time talk about science of Christmas trees.

Apart from looking and smelling wonderful, real trees use fewer materials and less energy to grow than artificial trees take to make...and if you recycle the tree afterwards (which you should) it can be turned into useful compost.

There are three main groups of plants that produce woody material:
  1. Softwoods like pine and spruce
  2. Hardwoods like oak and ash
  3. And woody monocots like bamboo and palm
This classification is botanical and has nothing to do with the hardness of the wood material (or any other mechanical property). Unless you're going to be particularly unusual this year, you'll be wanting a softwood as your Christmas tree...a cone shaped tree with needles.

Trees can be known by a common name and by a scientific name.

Common names differ around the world – even between English speaking countries. For example, the timbers known as redwood in North America (chiefly sequoia) are not the same as the timber known as redwood in Europe (Scots pine). This is why it is useful to use scientific (botanical) names in addition to the common name to avoid potential confusion.

Botanical names have two parts. The first word denotes the genus (family) and the second word denotes the species. The name is normally written in italics.

So types of wood that have the same genus name (e.g. Picea sitchensis and Picea abies) can be seen to belong to the same this case spruces (Sitka spruce and Norway spruce).

These days there are lots of different species of christmas tree to choose from. Here are a few examples...

Norway Spruce (Picea abies) is the traditional Christmas tree in the UK. It has a mid-green colour, a fine delicate foliage and a rich Christmassy scent. While fine in the chilly halls of Victorian times, it tends to drop its needles in modern centrally heated houses. Although we call it Norway Spruce the tree is native to a wide area including central and southern Europe, southern Scandinavia and the Balkans. This is also an important timber tree for the UK and is used to make timber framed houses. Mature trees grow about 35-50 metres tall.

Scots Pine (Pinus sylvestris) is the traditional North American Christmas tree. It has the advantage that it keeps its needles well so long as you keep the tree from drying out. The downside is that the needles are pin sharp. If you like your tree to be more tree than decorations this is a good one to go for as it tends to have lots of tightly packed branches. Scots pine is certainly not limited to has the widest natural range of any pine, growing right across northern Europe and Asia. This is also an important timber tree for the UK and is used to make timber framed houses. Mature trees grow about 25 to 35 metres tall.

Lodgepole Pine (Pinus contorta) has a cheerful yellowish green colour, and a sharp fragrance. It is native to the Rocky Mountains in North America and was introduced into the UK in 1855 because growers liked its ability to grow well on poor wet soils and its resistance to pests.

Korean Fir (Abies koreana) is a tree native to Korea that was introduced into the UK in 1913. Mature trees are relatively small, growing only about 10 metres in height. It has a bright silver undersides to the leaves, white buds and grows tightly packed branches making it an attractive choice.

Thursday, 29 November 2007

Virtual forest tour

UPM's Forest Life is a really beautiful combination of Flash, still photography, video and audio. It takes you on a tour of a Finnish forest looking at trees, plants, animals and people. Find out about how forests are managed sustainably for different purposes and how there is much more to a forest than just the trees.

The science of sound

Here we have a couple more films from the Prelinger Archive. The first from 1933 and the second made in 1948...back when a scrap of wood on a piece of string was carried by every child.

These videos explain the science of sound...what it is and how it's made. This will help you understand our video "measuring stiffness with sound".

Sunday, 25 November 2007

Careers in the timber industry

The UK's multipurpose forests provide environmentally friendly materials for all sorts of things and there are a vast array of different types of job out there.

For more information on jobs visit The Doorway and A Job In.

Friday, 23 November 2007

Chainsaw impersonation

Unbelievable but real...the Australian lyre bird can sing like a forester.

Wednesday, 21 November 2007

National tree week

"National tree week" starts today and runs until the 2nd of December. The Tree Council has organised several events around the UK celebrating trees and planting new ones.

If you want to know how to identify some of the trees that grow in the UK from their leaves you can play Kerf's leaf quiz on the main firrs website. There are more identification guides over at the Woodland Trust's Nature Detectives.

Tree planting is a great team building and feelgood activity to do in schools...and it goes on all over the world. This is a video made by a school in Costa Rica.

Trees can be planted as seeds, as small saplings, or as young trees several metres tall. Remember, although larger trees give instant satisfaction they also weigh more. It's also good to have a bit of expert advice to make sure the trees thrive and you know how to look after them.

You can still join in even if you don't have much outdoor space can plant a tree as a bonsai.

Monday, 12 November 2007

Deforestation and certification

This video from Greenpeace has a forceful message. It asks the question:

"Why destroy ancient forests for wood and paper, when it can all come from responsibly logged timber?"

Why indeed.

Well one reason this happens is that many people don't really understand how they can choose wood products that are environmentally sustainable - and come from properly managed forests. There is good wood and bad wood and we all need to understand the difference. Check out the certification schemes like FSC and look for the logos. Buying certified wood is a good encourages people to look after their forests.

Wednesday, 7 November 2007

Measuring stiffness with sound

It is very useful to know the engineering properties of the timber in logs before they are sent to the sawmill. Time and energy spent sawing up a log and kiln drying the battens is wasted if that timber later fails to meet the grade for construction. It would be much better to put that log to another use.

The science of sound allows us to do just that. The speed of sound through any material is related to the material's stiffness. In fact, stiffness equals density times the speed of sound squared.

That means if we can measure the speed of sound and the density we can calculate stiffness.

To do this we measure how long it takes the sound to travel from one end of the piece of timber to the other. Then it’s simply a case of speed equals distance divided by time. To explore the science further why not look at our whack-a-stick simulation or read about our exhibit at the Royal Society Summer Science Fair 2007?

This was one of the first videos we made. Annie and Heraa had just started their Nuffield Science Bursaries and we were practicing using the video camera. It just so happened that on the day, Peter Carter from Fibregen was visiting the laboratory to talk about his acoustic testing tool with John and Andy from the SIRT project.

We decided it was a good opportunity to make a short video, so Annie and Heraa asked Peter how it worked and we videoed Annie doing a demonstration.

This tool, the HM200, is called the Director, but people also call it the "Hitman". It is designed to work in busy, noisy timber yards but in the quiet of your own home or classroom you can make your own "non-destructive acoustic testing device". All you need is a microphone and a computer with some software that will analyse the frequency of sound. We have found that the free software called Audacity can do this well enough for a demonstration.

When you hit the end of the wooden batten with a hammer, the main sound you can hear is the sound of the first mode of resonance. The frequency of the first mode of resonance is the time it takes the sound to travel along the batten, bounce off the end and travel back down the length of the batten. This means the wavelength of the first mode of resonance is twice the length of the batten.

It sounds complicated at first, but it’s actually quite simple. All you need to do is hit the piece of timber and analyse the sound to find out what frequency it was mainly made off. So long as everything is working as it should, that is your first mode frequency.

To calculate the speed of sound in the timber:

(Speed of sound) = (wavelength) x (frequency) = 2 x (batten length) x (frequency)

And to calculate stiffness:

(Stiffness) = (density) x (speed of sound) x (speed of sound)

Here is some proof that we did not fake anything for the video. We took the audio recorded from the video and opened it in Audacity (we've extracted the sound of the hammer strikes so you can do this yourself). We then selected the sound of the hammer strike and selected "plot spectrum" from the "analyze" menu.

What we want to look at is the frequency spectrum – that's the graph with frequency on the horizontal axis and the level on the vertical axis. The higher the level the more of that frequency there is in the sound.

The sound contains lots of different frequencies, but we are mainly interested in the highest peak. This is a frequency of 554 Hz.

And if we look at what the figure on the laptop in the video it says 558 Hz. Pretty close huh?

Did you notice the time on the laptop clock? We don't work that late! That was New Zealand time. The laptop was Peter's and that's where he lives.

Monday, 29 October 2007


Some of the UK's forests were created hundreds of years ago as places for the rich to ride their horses...and now anybody can do it.

There are several jobs involved in working with horses in the forest and maintaining the bridalways. For small tree harvesting operations and tree thinning it is often best to use the traditional methods of horse logging. Horse loggers can move up to 10 tonnes of timber in a day leaving hardly a trace, and making hardly a sound. The big shire horses work best on flat lowland forests, while forests with hills and steep banks require smaller, more agile, horses. Horses are also used to move materials and equipment and to control invasive weeds like brambles and bracken.

Sunday, 28 October 2007

How trees are harvested

Think you know what a lumberjack is? A big guy with a beard, a checked shirt and an axe? Possibly saving girls in red hoods from wolves dressed as grandmothers? Well think again...

For starters the people (men and women) who take down the trees are called loggers or harvesters...and its all part of forest management, which also includes tree planting, silviculture, landscaping and a range of other 'forest operations'.

Technology has changed the job considerably from the days of yore. Chainsaws started to replace axes back in the 1920s, but these days most of the trees grown for timber in countries like the UK are felled by machines a bit like the ones you see on construction sites. These machines can cut a tree, strip the branches and cut the logs to length in a matter of they have a lot of other fancy gadgets GPS to locate the trees marked for felling. Other types of specialised machines are used to get the logs to the road and on to the sawmills.

All this is done while causing minimum damage to the forest floor and to young trees. The forest owners don't want their future timber crops to be put at risk...or any income they get from other uses of the forests such as recreation and tourism.

In some areas the land is so inaccessible that other methods have to be used, such as horses and helicopters ...or even submarines and machines that walk on legs!

Thursday, 25 October 2007

Reg Kehoe and his marimba queens

This one is a special educational content except the observation that marimbas are usually made of wood!

The bars for the lowest pitched notes are wider and longer, and gradually get thinner and shorter as the notes get higher.

Like the bars of a xylophone, the bars of a marimba are most commonly made from rosewood, but they can also be made from padouk and various synthetic materials.

Rosewood is the name given to a number of different timbers which have a rich dark red colour and a sweet smell. They are heavy and have strong resonance making them good for musical instruments. Unfortunately, many rosewoods, like Brazilian rosewood (Dalbergia nigra), are endangered due to over exploitation and should not be used.

The story of a forest ranger

This is another film from the excellent Prelinger Archive. This one was made in 1954 and looks at the job of the forest ranger in the USA. Again, you might recognise parts we used for our own videos.

Notice how the forests are talked about as a resource...but also how emphasis is placed on sustainable forestry and protection of the environment...even back in the 50s! Notice also how they stress the importance of avoiding forest fires. Back then many people smoked and lots of fires were started accidentally. Forest fires are still a big issue...all over the world (the UK included).

Monday, 22 October 2007

Wood for war - wood for peace

Ironically, the fact that we now have so many well managed forests in the UK is down, in part, to two of the most destructive events of the 20th Century: the two world wars.

During the First World War (1914 to 1918) Britain had great difficulty meeting the demands on timber - particularly for coal production and trench warfare. Britain's forests had been on the decline since medieval times and had been put under enormous pressure by the industrial revolution. Timber had been imported in large quantities for hundreds of years, but the war meant this supply was no longer reliable.

In 1919 the Forestry Commission was created and charged with reforesting the country with the help of private foresters. The idea was to improve the productivity of the forests and to create a large reserve of wood that could be called on in times of emergency.

Such a time came only a couple of decades later with the Second World War (1939-1945). During the war, the Commission's forests produced nearly one and a half million cubic meters of wood and nearly ten times more came from private estates.

These were times of great social change too. The 'lumberjills' were the forestry equivalent of the land army girls, but they weren't just felling trees - they were planting too...and the forests have been growing in size ever since.

Over the last 40 years or so the Forestry Commission has included conservation, ecology, recreation and tourism within it's objectives...and that's why we have today's multipurpose forests.

This is a video from the Prelinger Archive that was made during the Second World War looking at the same things from the American perspective. You might recognise parts we used in our videos.

Wednesday, 17 October 2007


Words cannot describe how much we love catapults. Some work because of the springiness of the wood (its elasticity) and some rely on its strength. The awesome trebuchet is in the second category.

Trebuchets work as huge levers. The short arm of the lever has a large counterweight on it and the longer arm has the projectile - which weighs a lot less. The potential energy of the counterweight is turned into kinetic energy of the small projectile. It's all in the physics - the bread and butter for engineers.

Warwick Castle has the world's largest. Check out their website with loads of historical facts and a flash game you can play.

If you're looking for a woodwork project why not try building your own mini trebuchet these kids did. The cola bottle is so cool! (8 minutes in)

Be safe though...not like the 'eccentric' guy in the third video!

Tuesday, 16 October 2007

Mountain biking

Have you watched our videos about Forestry Civil Engineering? Well this is one of the benefits of the work they do - mountain biking trails! Forests are very important to recreation, heath and tourism as well as being 'factories' for growing wood. If you live in Scotland check out 7stanes.

Monday, 15 October 2007

Wood and the environment

Today is "blog action day" so a good time to look at how the forest and timber industries impact on the environment.

Is using wood good or bad for the environment?

Well the answer is that it can be the moment.

OK, environmental issues are complicated so I'm afraid your going to have to concentrate while I try and explain this.

We all use wood products in our daily lives...and so it is very important that everyone understands this: there is good wood and there is bad wood.

Let's start with bad wood. Thankfully most people these days are aware that forests are being destroyed in some areas of the world. Some of this is because of logging for timber and some of it is because land is being cleared for other uses. This is a bad thing...for all sorts of reasons. As well as being the "lungs of the planet" forests provide homes to lots of animals and plants...and people too. Deforestation contributes to climate change and can also lead to landslides and floods. We hear a lot about the rain forests in South America, Africa and Asia, but forests are threatened in other areas as well...including Europe. Bad wood is wood that comes from:

  • Forests that are logged faster than they can regrow

  • Old growth forests, which contain important and rare habitats and which can't recover from logging

  • Forests that provide homes to endangered plants and animals

  • Logging that is linked to crime and poor treatment of native people

  • Logging that causes pollution or damage to the land

Buying bad wood is like buying a panda fur coat...and you wouldn't do that would you?

Now let's look at good wood. Wood is one of the few truly renewable materials we have. If we are careful about how we manage forests we can grow new wood to replace the wood we use. So long as forests are managed carefully they can provide wood forever. Indeed, thanks to responsible forestry for wood, the UK has more forests now than it had 100 years ago...and the forests are still growing.

Also, as trees grow they take carbon dioxide out of the air helping to combat climate change. When that wood is used to make products like furniture and houses the carbon is stored away and doesn't get back into the atmosphere until the wood product decays or is burnt...and that might be decades or even centuries. What's more is that we can make things out of wood that we would otherwise have to make from materials that cause environmental problems when they are made - like metals, concrete and plastics.

Forests can be factories for producing wood...and also provide lots of other good things too like homes for wildlife and nice places to go and exercise in.

So how can you know what's good wood and what's bad wood? Well, this is something that has been given a lot of thought in the last few years. There are now several "certification schemes" which aim to identify good wood. One of the best known is the Forest Stewardship Council (or FSC) which is supported by environmental organisations like Greenpeace, WWF and Friends of the Earth. You can find more information here and here. There is also an excellent virtual tour of a Finnish Forest explaining some of what is involved in sustainable forestry. And you can also learn a little more about the sustainability of different species by playing our timber trumps game.

Buying certified wood is a good encourages people to look after their forests. So look out for the certification marks.

Friday, 12 October 2007

Wood shrinkage

This is a delightfully retro video looking at the microstructure of pine wood and why it shrinks when it dries. It gets quite complicated with the terminology but has good visuals that help show how things work even if you don't understand the words. The things that look like air bubbles are meant to represent water droplets.

You might also want to look at our video about the chemistry of wood (on the firrs webpage).


Many people live in places where there is a risk of earthquakes. Timber is a good choice for houses in these areas because wooden construction is able to absorb a lot of movement and energy. Materials like brick and concrete are very stiff and crack easily so it is more complicated to make earthquake resistant buildings from them. Steel bolts and welds can also crack in situations like this.

In most cases the buildings won't actually be designed to survive a big earthquake without any damage at all. The most important thing is for the building to stay standing long enough so that people can get outside. People often choose to build their houses from timber because it makes them easy to repair after a natural disaster.

The first video shows a timber frame building and the second video shows a concrete frame building. Notice how this timber building is able to recover after large movements, whereas this concrete building can't.

Lolly stick bridges

We found loads of videos on the web of people's lolly stick bridge competions - from highschool science classes to engineering students at university...and in every single one people were having a lot of fun!

Now you could do this with lolly sticks (or popsicle sticks as the americans call them), modelling matches (the ones without heads), balsa wood, or with the wooden coffee stirrers you get in fancy coffee shops - you can buy a box of those quite cheaply. For fixings you could use glue, sticky tape, drawing pins, or even string.

Standing on the bridges looks a little bit risky - not least because everyone gets to know how much you weigh. Instead you could be more scientific and hang a bucket of weights off the bridge. The figures in this video are in pounds. There are 2.2 pounds in a kilogram.

There are lots of other things you can do instead of about cranes, towers, roofs or even fighting walls. You can even make a lolly stick bridge using no fixings at all - just lolly sticks and nothing else! Maybe one day we'll show you how...

Wood colour and chemistry

Here's a fun little video from the WoodWhisperer talking about how the colour of wood can change over time. This is all down to chemistry and something called oxidation. That's the same process that turns a sliced apple brown.

Sapwood is the outer part of the tree trunk - the wood that the tree is using to transport sap. The heartwood is the inner part of the tree trunk - the part of the wood that the tree uses to store waste chemicals...the extractives mentioned in this video.

As a tree ages the inner part of the sapwood slowly turns into heartwood. Heartwood provides structural support to the tree, but not much else and with very old trees it is common for the heartwood to be decayed away.

Different species of tree produce different extractive chemicals which explains why they can have such different colours.

Wednesday, 10 October 2007


Pykrete is a frozen mixture of water and wood fibre. Normal ice has very little tensile strength - it's brittle and cracks easily. The wood fibre helps spread the stress and bind together the ice making it many many times stronger.

It seems like a strange curiosity...but these days it is common to mix wood fibre with other materials like plastic and glue to make "composite materials" with improved properties.

Helicopter logging

There a several ways to get timber out of the forest, but perhaps the most spectacular method is by helicopter. This video shows a helicopter in action in Canada where the large distances and remoteness of the forests make this a viable option. It has been tried in the UK...the first time was in 1956 at Glenduror, near Fort William by the Forestry Commission.

Traditional timber frame 2

Here is a nice contrast to the "traditional timber frame 1" video. Again it's a class of students in the USA, but this time they are using modern machine tools for their carpentry. The most interesting bit is towards the end where you can briefly see some computer controlled robotic saws in action.

Timber frame DIY

It's possible to buy a timber frame kit house and to erect it yourself. Here is a video showing a photo montage of just that. The kit is made of small and light components that can be lifted into position without a crane. Timber frame is a very popular choice for people who build their own homes.

The green stuff is a special membrane that helps the building "breath" - a bit like a gore-tex jacket.

The stages of construction you can see here are:
1) The foundations (which would include all the drainage and other services)
2) Ground floor preparation (to get a nice surface and keep the water out)
3) The walls of the ground floor erected
4) The floor placed on the ground floor walls
5) The upper storey walls erected
6) The roof trusses erected
7) The windows installed
8) The outer brickwork laid
9) The roofing installed

Tuesday, 9 October 2007

Traditional timber frame 1

This video shows a group of students at a workshop in the USA building a traditional timber frame "post and beam" house using hand tools. Buildings like this are still being made (check out Carpenter Oak in the UK), but only for special projects. They require skilled craftspeople and large pieces of timber so are not practical for everyday houses... but can be very beautiful.

In contrast, a modern timber framed house is usually made from pieces about twenty times smaller in size! ....but that doesn't necessarily mean that a modern house won't last as long. The timber is used in a different way that allows for the forces to be carried by a larger number of smaller pieces. The wood is almost always a softwood like spruce, pine or fir which is dried in a kiln before it's used for building.

In this video it looks like the wood is a softwood, but post and beam houses are also often made from hardwoods like oak. In both cases, the timbers tend to be too big to be dried before use, so the connections must all be made to allow for the timber to shrink as it dries out as the building ages.

Check out "Traditional timber frame 2" to see the same sort of thing, but with modern power tools.

Japanese fighting walls

OK...we admit we don't know an awful lot about what is going on here because these videos are in Japanese.

What we think is happening is that people (engineering students?) are competing to create the strongest timber wall made with traditional carpentry joints. The walls are made to "fight" each other in pairs by putting a hydraulic jack between them that pulls them together (like tug of war in reverse).

The first video shows the construction of the walls and the second video shows the walls in action (perhaps the best video of the three). The third video shows the final stages of the competition.

The forces must be huge to cause these walls to break ...but you could stage your own miniature competition by making walls out of wooden lolly sticks or coffee stirrers.

Timber kit timelapse

This video shows a short timelapse of a timber frame house being looks like this was a demonstration during an exhibition. Many houses are now built like this in the UK. The timber kits are made as wall and floor panels in a factory and transported to the building site on a lorry in the right order for them to be placed on the foundations. A normal sized house can be put together like this in a matter of hours ...but this speed doesn't mean poor workmanship. In fact factory prefabrication (or so called "modern methods of construction") allow much tigher quality control than is possible outdoors on a busy building site.

Normally the house is then clad with brickwork to keep the wind and rain out...protecting the timber as well as the people living in the house. As far as most people can tell, the finished house looks like it is made from bricks.

The video seems to freeze 3 seconds in so you may need to drag the playhead to get it started again.

Friday, 5 October 2007

The walking harvester

A Finnish company owned by John Deere has developed a tree harvesting machine that walks through the forest like something out of a science fiction film. Even the wheeled and tracked harvesting machines are like a cross between a space ship and a sports 4x4.

The machine is useful in areas with difficult terrain ...where land has been turned to forestry because it can't be used for much else. Notice how lightly it treads...allowing forests to be managed for timber with the minimum of environmental impact.

The video shows the harvester in slow motion - it would be interesting to see how quickly it can really move!

Tuesday, 2 October 2007

Launch of the firrs DVD

In October we will be launching the "firrs DVD" - over two hours worth of videos about the science and technology of wood and the people involved a whole load more cool stuff.

If you live in Scotland you qualify for a free copy, which we can post to you if you let us know where you live.

We will be launching the new DVD at the Forest Education Initiative and Forest Schools Networking Event in Pitlochry on the 4th and 5th of October.