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.