Tree Structure

© 2008, Kenton Shepard

TREE NAMES

Trees have two sets of names.

scientific (Latin) names- are designed to separate tree species according to differences in their physical components such as leaves, cones, bark, flowers and wood structure.

common names, Tree species are more usually referred to by their common names which can be misleading. Common names for the same tree species sometimes change from one area to another. Sometimes one common name is used to describe wood from several tree species with very different properties and appearance.

For our purposes, the following list of tree species typically used for log building in North America gives both scientific and common names which we’ll use throughout the course. Inspectors will find buildings constructed from additional species.

COMMON NAME/LINK	SCIENTIFIC NAME
Cedar, Western Red	Thuja plicata
Cedar, Atlantic White	Chamaecyparis thyoides
Cypress, Bald	Taxodium distichum
Fir, Douglas	Pseudotsuga menziesii
Pine, Lodgepole	Pinus contorta
Pine, Red, Norway	Pinus resinosa
Pine, Ponderosa	Pinus ponderosa
Pine, White	Pinus strobus
Pine, Yellow, Longleaf	Pinus palustris
Redwood	Sequoia sempervirens
Spruce, Engelmann	Picea engelmannii

Source

Links in the table above give detailed information each tree species.

TREE TYPES

Seed plants, including trees, are divided into two classes, gymnosperms and angiosperms.

Gymnosperms- softwoods, mostly coniferous (don’t drop needles in the fall), provide the logs from which most log buildings are constructed. A few exceptions, larch (tamarack) and cypress, do drop their needles in the fall.

Angiosperms, hardwoods, mostly deciduous (do drop their leaves in they fall) such as oak and walnut are occasionally still used by builders.

The terms “hardwood” and “softwood” don’t correspond to wood density. Some softwoods (Douglas fir) are harder than some hardwoods and some hardwoods (Balsa) are softer than some softwoods. Almost all softwoods are evergreen trees with needles instead of broad leaves. Because the vast majority of logs used in building come from softwood trees, this course will concentrate on the softwoods.

TREE COMPONENTS

Plant species which grow taller than 20 feet when mature and have a dominant, single stem (the tree trunk) qualify to be called “trees”.  Plants which mature at less than 20 feet are called shrubs and aren’t used for building.

Source

Trees trunks divide into limbs which divide into twigs. Trunks, limbs and twigs all have the same general structure. Starting from the outside…

• Bark
  • Outer bark- composed of dead cells, protects the tree internal structure from fungi, insects, animal or mechanical damage, weather and fire. Bark is not considered to be wood.
  • Inner bark is composed of live cells called “phloem” through which food is transported from leaves to parts of the tree where growth takes place. This includes the tips of roots and twigs and the cambium layer of trunks and branches.
• Cambium- a thin (microscopic) layer which produces new wood cells from which all growth in trunk thickness takes place and which separates bark from wood. New cells produced on the outside of the cambium (cork cambium) layer move outward to become first phloem, which is alive, then bark, which is dead.

New cells produced on the inward side (vascular cambium) become sapwood, which eventually becomes heartwood.

• Wood- is divided into two types, both of which (in N. America) exhibit annual growth rings but which perform different primary functions in the tree.
  •  Sapwood- In addition to helping to support the tree, its main function is to transport water and mineral nutrients from the soil to leaves. Its cells also store carbohydrates and provide protection.
  • Heartwood, composed of dead cells, is a main source of structural support, but heartwood cells also store extractives (toxins) safely.
• Pith- soft wood which forms the center of the tree.