A tropical hardwood, a native evergreen, a deciduous conifer; there are various different ways to categorise trees. Some categories overlap, and some categories appear to have anomalies, but trees can broadly be categorised by
- leaf shape – broadleaves and conifers
- seed type – hardwoods and softwoods
- leaf retention – deciduous and evergreen
- provenance – native, naturalised and introduced
- region – tropical, subtropical, temperate and boreal
Broadleaves and Conifers
Conifers are trees with scale-like leaves or needles. Broadleaves have leaves which, whilst they vary in size and shape, are not scale-like or needles.
Hardwoods and Softwoods
The definition of hardwood and softwood has nothing to do with the physical qualities of the timber. The Longleaf pine and Douglas fir are softwoods but are mechanically harder than many hardwoods. Aspen and balsa are hardwoods but are softer than most softwoods.
Hardwoods are angiosperms (contained seeds), and therefore produce seeds with some sort of covering. This might be a fruit, such as an apple, or a hard shell, such as a hazelnut.
Softwoods are gymnosperms (naked seeds), and therefore produce seeds without a covering, albeit the seed of the yew tree have a partial covering called an aril. The aril is the edible, sweet, fleshy part that surrounds the small black seed nestled like an egg in a cup. The black seed is toxic and must not be chewed or swallowed. The word gym is a shortened form of gymnasium, from the Greek ‘gymnasion’, meaning public place where exercises are practiced. Standard dress at the gym these days is shorts, leggings and a top, but back in Ancient Greece, men commonly exercised naked – hence the root of gym, meaning naked.
Deciduous and Evergreen
Deciduous trees shed all their leaves every year, usually in autumn and produce new leaves the following year, usually in spring. Evergreen trees have leaves throughout the year albeit they shed a percentage of old leaves in autumn and replace them with new, usually the following spring.
Native, Introduced and Naturalised
There is much debate, and little agreement amongst academics, regarding which tree species, or how many, are native to the British Isles, or indeed what is a ‘native’ tree.
Very broadly, native trees are those trees that self-colonised the British Isles after the end of last ice age, and before the British Isles were cut-off from the rest of Europe by the rising sea levels. Examples include ash, silver birch and hazel.
Introduced, or non-native trees, are those which have been brought to the British Isles by people. Examples include apple, Douglas fir and horse chestnut.
Naturalised trees are those which have been introduced and are able to self-propagate.
Tropical, Sub tropical, Temperate or Boreal
- Tropical regions have year-round temperatures above 18°C, and lots of rain.
- Subtropical regions are sandwiched between tropical and temperate regions. They are similar to the tropical region, but not quite as hot or wet and have a noticeable chilly season.
- Temperate regions cycle through all four seasons.
- Boreal regions endure frigid temperatures year round.