Topic 2 Natural Resources

World Resources

Although much the world’s past forested areas were converted to agriculture and living space for the world’s growing population, about 27% of the world’s land mass remains covered with forest. The annual harvest of wood is approximately 3.5 billion cubic metres. About half of this is used for fuel. The rest is for forest products split between wood products (33%) and pulp and paper (13%). About 6% of the world’s wood is harvested from plantations, but this supplies about 23% of the world’s pulp. Canada has about 10% of the world’s forest resource. British Columbia’s annual wood harvest is about 60 million cubic metres per year. It may be noted that with a world population of 6 billion people per year and an annual population growth of 1.6%, for the world to keep harvesting wood at the current rate, it needs an increase in wood supply each year approximately the size of British Columbia’s annual harvest. These needs are being met by re-planting natural forests and by intensive plantations, particularly in southern climates which have fast growth cycles. Some examples are hardwood eucalypts in South America (7 yrs) and pine in southern US (25 years). In contrast, the conifers in Canada’s boreal forests mature at 75 years or more, and those in the BC Coastal rainforest in several hundred years. The world’s tree species may be divided into two major categories: hardwoods and softwoods. Softwoods are “conifer” trees that do not lose their needles during the winter. Examples are spruce, fir, hemlock, Douglas fir. Hardwoods are “deciduous” trees, that is, broad leaf trees that lose their leaves in the winter. Examples are maple, aspen, birch. The major traditional sources for paper are northern softwoods from Canada, Northern US, and Scandinavia. However, softwoods from southern climates, e.g. southern US, Chile, New Zealand, are growing in use. Hardwoods are also found in Canada and Scandinavia, but the principal new sources for this species lie in the

new plantation forests under development in South America and Asia. Hardwoods are growing in use in pulp and paper because of advances in papermaking technology that permit shorter fibres to be used where once only long fibred species sufficed. In Canada and BC, the major source of pulp is softwood. Over most of Canada, this comes from the boreal forest. This forest extends to the interior of BC. However, another distinct forest region exists on the BC coast and Vancouver Island—the temperate rainforest. The softwoods from this region differ from the “cold weather” softwoods, having properties more like southern pines.

Types of Trees

Trees are scientifically divided into two major categories: angiosperms and gymnosperms.

Gymnosperms do not produce flowers. Their seeds have structures such as cones, rather than a protective ovary. Conifers (needle-leaf trees) are a major group of gymnosperms.

Balsam Fir

Gymnos means naked, sperm means seed: gymnosperm = naked seeds. Gymnosperms developed during the Paleozoic Era and became dominant during the early Mesozoic Era. There are 700 living species placed into four divisions: conifers, cycads, ginkgos, and gnetales (such as Ephedra).

The conifers are a group of gymnosperms that reproduce by cones and have needle-like leaves (in general); includes the pines, spruce, fir, bald cypress and Norfolk Island Pine (Araucaria).

Coniferous (Softwood) trees keep their leaves throughout the year, shedding only the oldest leaves. Usually these leaves are lower down on the tree and do not receive as much sunlight as newly developed leaves higher up. Some of the best-known members of the conifer family are pines, spruces, firs, and hemlocks. The cones of the conifers are its flowers.

White Pine

Pines

There are nine species of pine trees native to Canada. The leaves of the pine are evergreen, needle-shaped, or linear. They grow in clusters that spiral around the trees' twigs and branchlets. Pines reproduce through their cones.

There are two groups of pines: soft pines and hard pines. Soft pines have leaves in clusters of five, and their cones are mostly without prickles, while hard pines have leaves that grow in clusters of two or three, and their cones are often armed with prickles.

Pines have always been important to the forest industry. Not only do they offer high-quality wood, they also have the ability to grow in poorer, drier soil.

The Spruces

Spruces have long, straight trunks with scaly bark. Their crowns are dense and narrow, with numerous pliable branches that often extend to the ground. Old trees, however, may be clear of branches for more than half of their height.

Five species of spruce are found in Canada. The leaves of all species are evergreen and usually under an inch long. They are needle-shaped and roll easily between the thumb and forefinger (except for the Sitka Spruce). The spruce reproduces through its cones.

Spruce wood is used for general construction, interior finishes, plywood and crating. Its naturally light color, low resin content and desirable fibre characteristics make it the preferred species for pulpwood production.

Firs

Canada has four species of fir. Except for the Balsam Fir, which can be found in every province, fir trees can be found only in British Columbia and Western Alberta.

Evergreen firs boast single, straight trunks and narrow pyramidal crowns. If growing in the open, the lower branches usually extend to the ground. Their leaves are single and arranged in spirals that appear to be in two rows along the twig. The bark of young trees is smooth and thin; later it becomes scaly and thick. Firs reproduce through their cones, which grow upright on the branches.

Because of their shape and aromatic fragrance, fir trees are highly prized as Christmas trees. Fir wood is also used extensively for pulp. In some parts of Canada its resin is collected and sold as "Canada balsam"; its leaf oils are also used for medicinal purposes.

The Arborvitae

The Arborvitae, commonly known as "cedar," is an evergreen tree with a stout trunk, short branches, a fibrous bark and flat, scaly leaves. It likes moist soil with good drainage, but can survive in drier conditions as well.

Young cedar cones are tiny and inconspicuous. They can be found at the ends of the twigs and have few scales.

Cedar wood is soft, aromatic, and light in color. It has long been valued for its ability to resist decay. The First Nations of the Pacific coast used the Western Red Cedar for totem poles, canoes and lodges. Today, it is a common building material for shingles, exterior siding, poles, posts and interior finishing.

Hemlocks

There are three species of Hemlock native to Canada: the Western and Mountain Hemlocks, which grow only in B.C., and the Eastern Hemlock, which can be found from Lake Superior to Cape Breton. Hemlocks thrive in moist, rainy areas, and can often be found near lakes, streams and swamps. Their leaves are evergreen

More gymnosperms / coniferous / softwood trees:

Abies balsamea Balsam Fir

Juniperus communis Common Juniper

Juniperus horizontalis Creeping Juniper

Juniperus virginiana Eastern Red-cedar

Picea abies Norway Spruce

Picea glauca White Spruce

Picea mariana Black Spruce *

Picea pungens * Colorado Blue Spruce

Pinus banksiana Jack Pine *

Pinus nigra * Austrian Pine

Pinus resinosa Red Pine

Pinus strobus White Pine

Pinus sylvestris Scotch Pine *

Pseudotsuga menziesii * Douglas Fir

Taxus canadensis American Yew *

Taxus cuspidata * Japanese Yew

Thuja occidentalis White Cedar; Arbor Vitae

Tsuga canadensis Eastern Hemlock

Angiosperms are flowering plants and their seeds are encased in a protective ovary. This division contains the larger number of species can be further subdivided into dicots and monocots. Dicots have two seed leaf structures and include many broadleaf trees such as the elm, maple and oak. Monocots have one seed leaf structure and include species such as the palm.

English Oak (form, leaf, flower)

Deciduous (Hardwood) trees are also known as broadleaf trees because the leaves are generally larger and wider than those of conifers. The larger leaf size means a greater surface area for photosynthesis, but it also means the leaf is too fragile to withstand winter conditions. Therefore, most deciduous trees drop their leaves in autumn.

Poplars

Poplars are one of the most common types of tree in Canada and can be found in every province. In fact, in some parts of the prairies they are the only trees present.

There are six species of poplar native to Canada. Fast-growing and short-lived, the poplar sheds its leaves in the autumn. Most species propagate through "suckers" that grow from the roots near the surface of the ground. This makes it easy for the tree to regenerate

after forest fires or harvesting. The leaves are alternate, long-stalked and single-toothed, with a few crooked and irregularly spaced veins.

Bark on young trees is a smooth white-green or yellow-green. On older trees it is furrowed and grey-green or brownish.

Poplar wood is lightweight and soft, and the growth rings are very faint. It is used for pulp, veneer, lumber, boxes and barrels for dry goods.

Birches

White Birch

Birches are best-known for their paper-like bark. On most species, it is smooth and white when the trees are young and peels off in long, thin layers. As the trees age, their bark becomes thicker and more irregular.

There are six species of birch tree in Canada. The most wide-spread is the White Birch, which can be found in every province, as well as in the Yukon and Northwest Territories.

Birch wood is very important to the lumber, plywood and pulpwood industries of Canada. Birches are also commonly used in landscaping.

Oaks

There are 10 species of oak in Canada. Most are found in the east; only the Bur Oak ranges into the prairies, and the Garry Oak is confined to B.C.

Oak leaves are simple, alternate and vary in shape and size. The fruit of the nut is the acorn.

There are three groups of oaks: white, chestnut and red or black oaks. White oaks have leaves with rounded lobes and teeth, and without bristles at their tips. Their bark is loose and scaly. Chestnut oaks share similar bark, but their leaves are regularly toothed, not rounded. Red or black oaks have leaves with sharp-pointed lobes. Their bark is firm and ridged.

Oak wood has long been prized for its strength and beauty. Hard and heavy, it is much in demand for furniture and floors, but oak trees grow slowly and supply has never kept up to demand.

Maples

The symbol of Canada and a source of national pride, it's surprising to learn that of the 150 species of maple in the world, only 10 are found in this country.

The maple leaf, which changes to a glorious yellow, orange or red in the autumn before falling to the ground, has three to nine veins, which radiate from the top of the stalk. The fruit of the tree is unique. It consists of two seed cases, each containing one seed and a long wing. In the autumn, these whirl to the ground like helicopter propellers.

Perhaps the best-known maple is the Sugar Maple. One of the most valuable commercial hardwoods in Canada, it is used for furniture, flooring and plywood. The sap of the tree is used to make another Canadian specialty: maple syrup.

Some more angiosperms/deciduous/hardwood trees:

Acer rubrum red maple

Acer saccharum sugar maple

Acer negundo box elder

Alnus viridis green alder

Betula alleghaniensis yellow birch

Betula papyrifera paper birch

Fraxinus americana white ash

Fraxinus quadrangulata blue ash

Populus alba white poplar

Populus alba white poplar

Populus balsamifera balsam poplar

Populus grandidentata big-tooth aspen

Quercus velutina black oak

Quercus alba white oak

Sorbus decora northern mountain ash

Ulmus americana American elm

Ulmus rubra slippery elm

The trees from our major product lines:

Both softwood and hardwood trees are used to make the various grades of pulp and paper. Hardwood pulps are used for grades that require bulk and smoothness such as fine writing papers. Softwood pulps are longer fibred and used in application that require high strength.

Softwood : Spruce-Pine-Fir species (SPF)

• Jack Pine • Spruce • Red Pine • Larch • Balsam • Douglas Fir • Sub-alpine Fir

Hardwood

• Maple • Yellow Birch • White Birch • Red Oak • Aspen

For more about trees see the website: “Trees in Canada” http://www.treecanada.ca/trees/index.php

The Structure of a tree Trees are living entities. They consist of cells that reproduce. Like people, trees grow up, get broader in size, get old, become susceptible to disease, and eventually die. During their lifetime, they may become infested with disease, for example the recent pine beetle infestation in BC. In the boreal and sub-boreal forest, trees reach maturity at about 50 years and have a lifetime of about 100 years. In most cases, when they get old, they die and dry out. They then become very susceptible to forest fires, which is nature’s way of regenerating the forest. In Canada, more wood is lost annually to forest fires than is harvested by the forest products industry. The basic element in a tree is a cell. These are “fibres”. When removed from trees, they are called pulp. Fibres are the elements from which paper is made. Although they have specific anatomical names e.g. tracheids in the case of softwood, for the purpose of these lectures we will simply call them fibres.

Crown

Roots

Figure: Juvenile / mature wood and transversal / Tangential / Radial planes of a tree.

Trees grow upward and outward. This growth produces fibres of differing properties within a tree. These are: heartwood, sapwood, juvenile wood, mature wood. The tree growth takes place just under

the bark in a “cambium layer” where the cells reproduce. In this zone, called sapwood, the cells are physiologically active, storing food and water and carrying sap. Eventually as newer cells are produced, the older ones nearer the tree centre no longer function physiologically and are called heartwood. The fibres, oriented vertically in the tree, are held together in a matrix by a polymer called lignin. This acts as a glue. As the tree grows, the nature of the cells change, leaving an inner core called “juvenile wood’ formed early in the tree life, and “mature wood’ formed later in its life, as shown in Fig 1. There are two growing seasons for trees. In the spring, cells grow to large hollow thin-walled fibres. In the summer period, they grow to a cell having a smaller hollow area and thicker wall. These two distinct types of fibres in a tree are called “early wood” and “latewood”, or “spring wood” and “summer wood”. They are visible in a tree cross section as annular rings. Cross Section

Tree cross-section

From the cross section of a tree we can see the following features: Outer Bark: The outer, mostly dead tissues (outer bark) form a protective barrier between the plant axis and the abiotic and biotic environment.

Inner Bark: The inner tissue (secondary phloem), including living

hloem: Living part of bark

ambium: thin layer of generative tissue lying between the bark and

cells (inner bark), is where sugar transport for the plant occurs, and the inner bark also can have defenses against herbivores, such as cells with tough cell walls (secondary phloem fibers or sclereids) or cells and tubes filled with bitter or toxic chemicals. P Cthe wood of a stem, most active in woody plants. The cambium produces new layers of phloem (bark) on the outside and of xylem (wood) on the inside, thus increasing the diameter of the stem. Sapwood: Newly formed outer wood lying between the cambium and the heartwood of a tree. Usually light in color and is active in water conduction. Heartwood the central, woody core of a tree, no longer serving for the conduction of water and dissolved minerals; heartwood is usually denser and darker in color than the outer sapwood. Growth Ring

he layer of wood growth added each growing season to the diameter of the Ttree. In the temperate zone the annual growth rings of many species such as oaks and pines are readily distinguished because of differences in the cells formed during the early and late parts of the seasons.

The annual ring is composed of layers of earlywood and latewood. Earlywood: The less dense wood formed during the early stage of a growth season, eg. the spring or rainy season, when the tree is growing quickly. Also sometimes called springwood. Earlywood and latewood together form the growth rings of a tree. Latewood The denser wood formed during the later stages in a season, when growth slows down, eg. summer and autumn or the dry season. Also sometimes called summerwood, earlywood and latewood together form the growth rings of a tree. Note that the earlywood and latewood differ tremendously in their papermaking properties. The earlywood fibres have narrow walls that allow them to conform together into a well formed smooth, strong sheet of paper, while thick-walled latewood fibres do not conform well and make a bulky, porous sheet that is not as strong. Many tree species differ in the ratio of earlywood to latewood fibres. This ratio is a major indicator of the tree/wood quality for lumber and pulp.

Types of cells There are many different types of cells in a tree and in general there are a greater number of cells in angiosperms most likely because they are more advanced in evolution.

Fiber Tracheids (Fibres) - As the primary water-conducting elements in gymnosperms and seedless vascular plants, tracheids are elongated cells (average 1 millimeter long) that are closed at both ends and appear square in cross-section in the xylem tissue of trees. The thick, lignified walls are perforated so that water can flow from one tracheid to the next. The xylem of conifers (pine trees) and ferns only contain tracheids. Vessels (also Wood Vessels, Xylem Vessels, Trachae, or Pores) - As the water-conducting elements of angiosperms, vessels are characterized by the water-filled tubes of the xylem of wood in hardwood tree species. Malpighi misnamed them as trachae in the seventeenth century on the ill-conceived notion that vessels were an important common element in plant and animal anatomy. Composed of numerous thick-walled, relatively large diameter cells, vessels are as long as the entire shoot in some plant species and are considered more efficient than tracheids in moving water. Strengthened with lignin, xylem vessels are non-living ducts and are deposited in spiral

and ring patterns characteristic of the tree species, usually perforated y pits.

ous (c) diffuse porous.

b The vessels can be arranged in three way throughout the growth ring:: (a) Ring porous, (b) Semi-ring por

Pits (or Bordered Pits) - The openings in the cell wall for connection between tree cells consisting of a pit cavity and pit membrane. Pits allow the exchange of solutes in woody plants and are very porous, allowing the movement of water and ions from tracheid to tracheid. Bordered pits are typical for tracheids (gymnosperms and seedless ascular plants) while wood vessels are more typical of flowering lants (angiosperms). The balsam poplar is characterized by both

hose in gymnosperm wood. Pith rays are

vpsimple and bordered pits. Rays (also referred to as Pith Rays or Medullary Rays) - Rays are ribbons of cells aligned radially in a tree. Constructed of parenchyma cells arranged with their longitudinal axes oriented axially or radially, rays occur in wood as single or multiple layers (storied and seriate, respectively). The rays of angiosperm wood rarely contain tracheids

nd are larger than tatypically viewed in the cross-section of a tree trunk running radially rather than in concentric circles. Parenchyma (also referred to as Ground Tissue or Soft Tissue) - Cells in a tissue of a tree that are concerned with function rather than structure. Parenchymal tissue, composing the bulk of all plant tissues, has specialized embedded cells that are characterized as large or small, thin-, medium- or thick-walled and usually contain a central vacuole. In plants, parenchyma cells perform the functions of storage (cells of the white potato and the pulp of fruits), assimilation (chloroplasts predominate in parenchymal-dominated leaves), or

wound healing (resins and gums). In conifers, parenchyma cell arrangements form resin ducts or canals in the rays, usually at the

nd of each growth ring. Along with the rays, the parenchyma forms

ent is used as an identifying characteristic for tree species.

ethe food storage system of the tree. Parenchyma is often lighter in color than the rest of the wood and the pattern of its arrangem

Relative sizes of the different fibres (cells)

Fibre (Cell) structure

MicrofibrilAngle

SecondaryWall

PrimaryWall

S3S2S1

↖

MiddleLamella

Primary Wall Net-like covering layer formed by the microfibrils on the fiber surface. Microfibrils form an irregular, interwoven pattern. Secondary Wall: Microfibrils occur in parallel arrays or sheets of

referred orientation. Has three distinct regions: S1 Layer:

• microfibrils are oriented more along the longitudinal axis of fiber

• fibril angle is between 50-70° • 3-4 lamellae (layers) thick

S2 Layer • forms the bulk of the cell wall material • contains majority of mass of fiber • determines properties of fiber • fibril angle is only about 10-30° • in general, as microfibril angle decreases, the fiber strength

increases and the fiber stretch decreases S3 Layer

• relatively similar to S1 layer in construction • fibril angles are 50-90° • also called the tertiary wall

Middle Lamella: The area between cells that is rich in lignin.

p

Fibrils Fibrils are crystals of cellulse. The angle at which the fibrils make with respect to the axis in the secondary wall significantly affects the strength of the fibre.

θ

Chemical structure of the cell

se and Lignin. However, there are many other chemical

the fi

Wood cells are primarily made up of three chemical constituents: Cellulose, Hemicellulo

compounds found in trees they are not discussed here. In general the fibres are made up of cellulose crystals that are surrounded by a thermo plastic polymer called lignin. Between the lignin and the cellulose you can find hemi-celluloses, as indicated in

gure below.

Cellulose is composed of linear chains of covalently linked glucose residues. It is very stable chemically and extremely insoluble. In the primary cell wall exists one glucose polymer of roughly 6000 glucose units, in the secondary wall their number is increased to 13 - 16000 units. Cellulose chains form crystalline structures called microfibrils. A microfibril with a diameter of 20 - 30 nm contains about 2000 molecules.

Crystalline and non-crystalline sections alternate. In crystalline ones forms the cellulose three-dimensional lattices due to the formation of

e highest possible number of hydrogen bonds. This high degree of thorganization is not achieved in the other sections, called paracrystalline. Crystals polarize light. By studying cellulose between crossed polarisators can the main orientation of the microfibrils be determined. In the primary wall they do occur in every possible orientation (disperse texture). During the development of the secondary wall are they deposited in layers (as lamellas). The microfibrils of each layer are parallel to each other (parallel texture). Their orientation changes from layer to layer. Often, especially in very strong cell walls (like those of cotton) are the microfibrills arranged screw-like around the cell's axis. In such cases this changes the turning angle from layer to layer (screw-like texture).

OH O

O HO HO

O

HO O

O

OH

OH

OH

OH

O

O

O

O

OH

OH

HO

HO

HO HO

HO

E

D

Cellulose Molecule

C

O

B A

Fiber

Cellulose fibers usually consist of over 500,000 cellulose molecules. If a fiber consists of 500,000 cellulose molecules with 5,000 glucose resides/cellulose molecule, the fiber would contain about 2.5 bi on H-bonds. Even if an H-bond is about 1/10 the strength of a covalent bond, the cumulative bonding energy of 2.5 billion of them is awesome. It is the H-bonding that is the basis of the high tensile strength of cellulose.

emicellulose is a polysaccharide composed of a variety of sugars

lli

Hincluding xylose, arabinose, mannose. Hemicellulose that is primarily xylose or arabinose is referred to as xyloglucans or arabinoglucans, respectively.

Hemicellulose molecules are often branched. Like the pectic compounds, hemicellulose molecules are very hydrophilic. They become highly hydrated and form gels. Hemicellulose is abundant in primary walls but is also found in secondary walls.

Crystalline Regions (highly

Amorphous Regions

Lignin is a complex phenylpropanoi posited in plant cell walls. Precursors of lignin are the three aromatic alcohols, coumaryl, coniferyl, and sinapyl alcohols which give rise to the p-coumaryl, guiacyl, and sinapyl-propane subunits, respectively. These precursors are linked by a wide variety of bonds in the final polymer. Polymerization can continue as long as activated precursors and space in the wall are available. The polymer tends to fill all of the space in the wall that is not occupied by macromolecules, it displaces water as it does so. The result is a very strong, hydrophobic meshwork which surrounds other wall components and cements them in place. Lignin is found principally in the sclerenchyma and in the tracheids

nd vessels of the xylem. It is also found in other cells in response to

d polymer which is de

ainfection or certain other external stimuli. Lignin is responsible for adding rigidity and strength to cell walls and for providing barriers to diffusion and infection.

Extractives Miscelaneous components that are soluable in acetone are called extractives.

• They consist of sugars, amino acids, simple fats and carboxylic acids.

• Mostly they are intermediate compounds from metabolic processes

• Found in sapwood and inner bark (live part : Phloem) • Dissolve rapidly in alkaline (kraft) pulping. • Can break down pulping chemicals requiring a higher

concentration. • May also negatively affect the colour and bleachability and

wettability of pulps. • Diminish transport of pulping chemicals into the wood.

Inorganic Compunds These compounds enter through the roots and contain alkaline earths: Calcium, potassium, magnesium and silica. They create problems of wear, especially in mechanical pulping. They don’t burn. Measured as ash content of pulp. Chemical distribution in the cell wall The chemical components of the cell wall (i.e. cellulose, hemicelluloses, &lignin) are not uniformly distributed throughout the cell wall.

Note:

• The middle lamella contains much of the lignin. • Cellulose is the major constituent of the cell wall

on Wood Fibres: pply.

a. Original papers made from cotton. b. Nearly pure cellulose c. Source from rags, textile cuttings d. Very long fibres and very strong.

2. Linen: Flax stalks or cuttings. Currency is often made from linen/cotton

3. Bagasse: Residue from sugar manufacture. 4. Bamboo: Fast growing, 1.7-3mm long fibres. Lots of different

species. 5. Hemp: Fast growing long fibred.

• Hemi-celluloses are a significant percentage of the cell. NPrimarily used where wood is in short su

1. Cotton

Variation Variability of fibres is one of the main problems affecting pulping and papermaking in BC. It is difficult to make a high quality product if the raw material is continuously changing. Factors affecting variation:

1. Between species (BC has 27 subspecies of pine trees) 2. Between Tree variations.

a. Northern/southern/coastal/interior. b. Growing conditions (hills / valley) c. Genetic variation

3. Between ring variations. Juvenile / mature wood, changing climate

4. Within rings. Early wood / latewood Summary of important papermaking fibre properties for the main

ulping species p