⁠⁠Tree Bark: Description, Structure, Texure, Classification, Colours and Uses

Tree bark is the outermost layer of the wood that protects the inside of a tree. It comes in many different shapes, colours and textures. From smooth grey skin to the deeply furrowed plates and the peeling, papery curls, tree barks give us insights into various plant adaptations and unique characteristics of each species. In this article we will learn about different types of tree barks, their characteristics, types and uses.

Table of Contents

• What is a Tree Bark
• Structure of a Tree Trunk
• Physical Characteristics of a Tree Bark
• Classification of Tree Barks
• Uses of Tree Barks

What is a Tree Bark

The word bark is derived from the old Norse word ‘bǫrkr’ which means tree bark. A tree bark refers to all the tissues of a woody stem, branch, or root that drive the secondary growth of plants and shrubs. More than just an outer covering it is a complex and functionally diverse tissue system, responsible for the survival and ecological success of woody plants. Let’s learn about different types of tree barks along with their different characteristics and uses.

Structure of a Tree Trunk

To learn the physical properties of tree bark, it is necessary to know the tree trunk structure. A tree stem has five different layers:

Pith or Heartwood: It is the innermost layer of the tree trunk with soft tissue that gives structural support to the tree.

Xylem: This layer is an outer covering of sapwood that plays a major role in carrying water and nutrients upwards from the roots to the other parts of the tree.

Vascular Cambium: It is a thin cylindrical layer that drives the secondary growth of the tree by producing new xylem.

Phloem: It is an inner layer that carries food produced by photosynthesis from leaves to the rest of the plant.

Phellogen: Also known as cork cambium this layer generates cork cells on the outside and phelloderm inside of it.

Periderm: It is the outermost layer of the tree trunk that defends the tree against fungi, insects and diseases. The cork in this layer is the last part that dies and becomes thick. It creates a waterproof layer to protect trees from moisture and dehydration. 

Physical Characteristics of a Tree Bark

All the layers defined above together form the tree bark and there are different characteristics of each tree bark that differentiates one species of tree from another. There is a wide range of physical characteristics each tree bark exhibits such as colour, textures, shapes and surface pattern. These characteristics also decide the bark's ecological functions and its practical applications.

Colour: A tree bark can be found in varied colors ranging from grey, brown, red, white, orange, green and even multi-coloured patterns such as the bark of rainbow eucalyptus. The colour of the tree bark is determined by the pigments present in the tree such as chlorophyll, tannins and other phenolic compounds.

Texture: There are tree bark textures that can range from being perfectly smooth to deeply wrinkled, scaly, plated or peeling. The texture of the bark is largely defined by the pressure placed on it from wood growing inside to expand the tree's diameter. The outer layer usually becomes dead, scaly and non-elastic due to this undergoing change.

Thickness: Bark thickness differs across various species and increases more as the tree ages and the trunk grows in diameter. Some of the species such as birch often have a thin bark only a few millimetres in width even at the maturity stage, while some other thick-barked species such as cork oak can develop a bark 30 cm in diameter.

Weight: Cork tissue is generally lightweight due to its cellular structure. Cork cells are dead at maturity and their interior spaces are filled with air rather than liquid.

Classification of a Tree Bark Based on Surface Texture and Pattern 

Tree barks can be classified into different types based on their physical appearance. It is also a detrimental factor in identifying species even when leaves or fruit are unavailable.

Bark Type	Description	Example Species
Smooth Bark	Thin, unbroken surface often retains photosynthetic capacity	American beech or young birches
Fissured Bark	Bark develops vertical or interlacing grooves separated by raised ridges as the tree ages	Oaks and ash (Fraxinus spp.)
Scaly Bark	Bark breaks into small, irregular, overlapping plates or scales	Pines (Pinus spp.), black cherry (Prunus serotina)
Plated Bark	Bark separates into larger, flat, rectangular or polygonal plates	Ponderosa pine, persimmon (Diospyros virginiana)
Peeling/Exfoliating Bark	Bark separates and peels away in sheets, strips, or curls, often revealing colourful inner layers	Paper birch (Betula papyrifera), river birch, eucalyptus, sycamore
Ridged Bark	Narrow, often spine-like ridges run vertically along the trunk	Sweetgum (Liquidambar styraciflua), elm
Warty/Corky Bark	Bark develops thick, irregular protuberances or corky outgrowths	Hackberry (Celtis occidentalis), winged elm
Spiny Bark	Bark or associated structures bear sharp spines or thorns	Honey locust (Gleditsia triacanthos), silk floss tree

Uses of Tree Bark

Tree bark has been utilized for over years by many civilizations for various purposes. It continues to serve significant roles across the field of medicine, industry, agriculture, construction and culture. The diverse chemical and physical properties of tree barks make it a uniquely versatile and naturally important product.