Virtually since the beginning of human civilization, the bark and roots of conifers have been used for a variety of purposes. For example, across Eurasia, a product known as pettu, made from the inner bark of Pinus sylvestris, was used as survival food (Johnson Gottesfeld 1992). The inner bark of P. sylvestris also formed a considerable portion of the diet of the Laplanders (Gaertner 1970). In Japan, the bark of Cryptomeria japonica was used as roofing material (Hora 1981). Tannin, taken from the bark of several species of conifers, has been used to tan animal skins and produce leather. Recently, taxol, a product from the bark of Taxus brevifolia, has been found to be valuable in the treatment of certain cancers. In addition, initiatives to increase utilization of large volumes of waste bark from the wood products industry have resulted in a number of innovative uses, including decorative ones.
Several forest dwelling, indigenous tribes of north-western British Columbia, Canada, obtained a staple food by processing the cambium and inner bark of the western hemlock, Tsuga heterophylla, into "cakes." These were stored in a dried form and could be reconstituted by soaking chunks of dried cake into water. The Haisla and Gitksan devoted considerable attention to obtaining and processing hemlock cambium. Suitability of a tree was determined by making a test scraping of the bark and tasting it for tenderness and sweetness. Certain sites were known for their high quality cambium.
The Haisla gathered western hemlock bark in late June or July. Trees about 60 cm in diameter were chosen for harvest. Bark was removed and the inner bark was scraped off of the inside of a bark section with a special curved knife. The tree was usually felled or stripped and girdled while standing. A single tree yielded 2-3 baskets of cambium. Each basket could be processed into 4-5 cakes. The cambium was pit-cooked overnight and was then pounded to soften it. The pounded bark was formed into cakes and sun dried or smoked. Each family stored about 30-40 cakes for winter. A more contemporary version of this technique involves processing the cambium in canning jars. These cakes were used as a sweetener for other foods.
The cambium of lodgepole pine, Pinus contorta, was second in importance to hemlock cambium as a food source. It was used by the Wet’suwet’en and Gitksan tribes in the interior of north-western British Columbia. The inner bark was harvested from young standing trees in May and June, a time when the bark is of maximum sweetness and is loose and easy to harvest (Johnson Gottesfeld 1992).
Other indigenous tribes across North America also made use of conifer
bark as food. The Adirondack indians of northern New York State used the
bark of a number of conifers for food. Bark was such an important part
of their diet that their name in the Mohawk indian language means "tree
eaters" (Gaertner 1970).
The bark of several species of indigenous conifers were used by the Gitskan,
Haisla and Wet’suet’en tribes of north-western British Columbia, Canada,
to help cure a variety of illnesses (Table 5.1). In some cases, extracts
of pure bark were used. In other cases, bark was mixed with the foliage
of devil’s club, Oplopanax horridus and other shrubs.
Uses of conifer bark for medicinal purposes
by indigenous tribes of North-western British Columbia, Canada
||Illness||Tribes which used remedy|
|Picea engelmanni x glauca
|Tonic, flu, colds
Tonic, flu, colds
Cleaner, gall bladder,
Swallowed sharp objects
* Often mixed with foliage of devils club, Oplopanax horridus
and other shrubs.
Source: Johnson Gottesfeld (1992).
The Quinault tribe of north-western Washington and the Karuk tribe of northern California, United States, peeled, dried and boiled the roots of the Pacific yew, Taxus brevifolia, to make tea. The Quinaults drank the liquid as lung medication (Gunther 1973), while the Karuk used it to relieve stomach aches and kidney problems (Davis and Hendrix 1992).
The bark of Cedrus deodara has been used in India as a medicine
for fevers, diarrhea and dysentery (Maheshwari and Chhaya Biswas 1970).
The inner bark of eastern hemlock, Tsuga canadensis, is cinnamon red to purplish in colour and is the source of a natural dye. In the Southern Appalachian Mountains of the United States, hemlock bark has been used for dying wool a brown colour. Hemlock bark also dyes leather a reddish tone. The bark from the roots of this tree is used to dye basketry materials and produces a range of colours depending on the chemical mordant used in the dye bath. Hemlock root bark dyes raffia pink without a pre-mordant, pink-tan with alum, rust with chrome and brown with copper sulphate (Hart and Hart 1976). In the New England States, both indigenous tribes and early European settlers used also bark of this tree as a dye source (Hussey 1974).
The bark of the western hemlock, Tsuga heterophylla, produces a reddish dye that the Coastal Salish indians of Vancouver Island, British Columbia, Canada, used for several purposes. Young girls used this dye to paint their cheeks. Indigenous tribes in Washington, United States, to colour paddles also used dye from the bark of western hemlock, fish nets and spears (Turner and Bell, 1971).
In India, the roots of Juniperus communis are used to produce
a purple-coloured dye.
The inner bark of the western red cedar, Thuja plicata, and Alaska yellow cedar, Chamaecyparis nootkatensis, were used for a variety of items by the indigenous tribes of the Pacific north-western region of North America. During the transition from spring to summer, women went into the forest and sought out young cedar trees. After saying a prayer for the tree’s soul, they notched the bark near the base, loosened it carefully and tried to tear a long strip of bark free, tearing upward. The inner, lighter bark was separated from the rough outer bark and brought home to be used in various ways. Raw bark was often transformed into a water ladle or a small canoe. Of greater importance, however, was the prepared bark that was beaten until it became a soft fibre. It was then separated into strips and bands of varying width. This fibre was one of the raw materials used for coarser woven products such as mats, baskets and shawls, cord for hanging fish in the smokehouse and lashings for shelters (Bruggmann and Gerber 1989).
The bark of Thuja plicata, pounded into a soft fibre with a special stone or whalebone tool, was used for bandages and diapers by the Haisla and other coastal tribes. Spun bark fibre was twined into clothing, blankets and capes and was also used for string. The Haisla revered the inner bark of Chamaecyparis nootkatensis because this tree had a superior softness. Only nobility wore the fibre of this tree. Whole red cedar bark was stripped from trees in sheets to serve as roofing and for tarpaulins. The Wet’suwet’en tribe used the bark of spruce, Picea glauca and Picea engelmanni, for roofing shelters. It was more available than cedar bark, but less durable. (Johnson Gottesfeld 1992).
Baskets and various articles of clothing were made from strips of cedar bark, often used in combination with other materials such as fine, peeled roots of spruce, Picea sitchensis, and grasses. A twined weaving technique using fibre of cedar bark and dried grasses was done by the Nootka Indians, who inhabit Vancouver Island, Canada, and the north-west corner of the Olympic Peninsula of Washington, to make baskets. Roots of spruce and cedar were well suited for the coil technique, which guaranteed a watertight weave. When using this method, the weaver works with two weft strands, which are crossed over each other at each warp strand. This process results in a tighter weave than the less useful plaiting technique (Bruggmann and Gerber 1989).
Weavings made from roots of spruce are works of art. Examples include watertight whaler’s hats woven by Haida weavers such as Isabella Edenshaw (1858-1926) and painted by her husband Charles Edenshaw, a famous Haida artist (1838-1920). Typical designs depict animals indigenous to the region such as ravens, whales, salmon etc. Several contemporary artists have maintained the tradition of spruce root basket weaving. These include Haida weavers Holly Churchill-Burns and her sister April Churchill-Varnell of Ketchikan, Alaska, who learned the technique from their grandmother, Selina Peratrovich of Masset, Queen Charlotte Islands, British Columbia, Canada (Bruggmann and Gerber 1989). Haida hats woven from cedar bark currently sell for around US$295.
The Tlingit of south-eastern Alaska also made spruce root baskets. The women of the Chikat Tlingit made decorative hats from spruce roots. A hat for a chief would be decorated on top with the skin of an ermine and painted with intricate designs such as cylindrical rings which are said to represent the number of potlatches (a traditional festival) hosted by the wearer. Tlingit baskets woven from spruce roots and multicoloured grasses contained intricate patterns. A blue colour for the patterns was created from crushed huckleberries (Bruggmann and Gerber 1989).
Local indigenous tribes which occupied what is now known as the New England States of north-eastern United States used the fine roots of Picea glauca, P. mariana and P. rubens to make robes, tackle, woven mats and thread (Hussey 1974).
In California, United States, the Pomo Indians used the roots of Tórreya californica, an endemic conifer, to make baskets (Burke 1975).
The Cahuilla Indians, a tribe that once occupied the Mojave Dessert of California used the fibrous bark of Juniperus californica to diaper infants.
The Thomson and Lilloet Interior Salish of British Columbia, Canada, used sheets of bark for various purposes. The smooth bark of Abies spp. was used for roofing and canoes. The bark of Picea engelmannii was used for roofing, canoes, baskets and utensils, the bark of Thuja plicata was used for roofing, wall lining and mats and the bark of Pinus contorta was used for lodge coverings (Turner 1988).
Today, most bark products of the indigenous forest dwelling people of the Pacific north-west region of North America have been replaced by either manufactured or agricultural products. However, some uses still persist, especially uses of medicinal barks gathered by older people for self-treatment or treatment of friends and relatives. Bark of cedar and willow, Salix spp., are still preferred cords for hanging fish in smokehouses. Cedar and spruce basketry are enjoying a revival as handicrafts for cash sale. Their functional importance, however, is virtually nil because of manufactured substitutes (Johnson Gottesfeld 1992).
Strips of outer bark of Juniperus excelsa have been a traditional
roofing material in villages in the Province of Balochistan, south-western
Pakistan, which are located in close proximity to forests of this species.
This material is still widely used today (Author’s observation).
Taxol is a plant-derived anti cancer drug. Its anti cancer properties were discovered during clinical trials conducted by the National Cancer Institute (NCI) of the United States. This compound was first isolated from the bark of the Pacific yew, Taxus brevifolia, a slow growing, small to medium tree which is a component of the understory of old growth forests of the Pacific north-west region of Canada and the United States (Fig. 5.2, 5.3). Taxol is also found in the bark and needles of related species of Taxus throughout the world.
Clinical studies of taxol first began in 1983 and, by 1988, preliminary results suggested that this material was active against ovarian cancer, a form of cancer generally resistant to chemotherapy and from which nearly 12 500 women die each year. Tests on more than 200 patients with recurrent ovarian cancer indicated that at least 30 percent of the patients had responded to some degree. These studies also indicated that taxol has potential for treating other types of cancer, including advanced breast cancer. In 1992, the Food and Drug Administration of the United States (FDA) approved a new drug application for taxol from the bark of Taxus brevifolia for commercial use (NCI 1992).
As a result of this research, there was a sudden, high demand for the bark of Pacific Yew and during the late 1980s, NCI contracted to have yew bark collected from National Forest lands, primarily in Oregon and Washington. Approximately 60 000 kg of bark were subsequently collected. NCI then contracted with a private pharmaceutical company, Bristol Myers-Squibb (BMS), to develop the drug, find a reliable taxol source and bring the drug to market. BMS then harvested over 700 000 kg of dry yew bark from federal forest lands (Forest Service and Bureau of Land Management [BLM]) in 1991 and 1992. Collection of yew bark provided jobs for 550 workers from local communities from May through August 1991 and for 1 115 workers for the same period in 1992 (Wolf and Wortman 1992).
Figure 5.1: A building in Balochistan Province, Pakistan with roof made from strips of the bark of Juniperus excelsa.
Because of concern over the potential adverse environmental impacts of an increased demand for slow-growing trees with limited natural range, the Federal Pacific Yew Act (Public Law 102-335 106 Stat. 859) was passed by the United States Congress and signed into law in August 1992. This act ensured that the Forest Service and BLM would carry out efficient collection and utilization of Pacific yew for taxol, specify conditions of sale of Pacific yew from federal forest lands, ensure long-term conservation of Pacific yew and prevent waste of this resource. An environmental impact statement was prepared jointly by USDA Forest Service, the USDI Bureau of Land Management and the Food and Drug Administration of the United States Department of Health to examine alternative harvesting schedules for Pacific yew. For the five-year period 1993-1997, the EIS defined an annual harvest level from federal forest lands to be from 117 000 to 175 000 kg of dry bark and/or from 312 000 to 468 000 kg of dry needles, approximately, from an estimated number of 52 000 to 78 000 yew trees (USDA Forest Service 1993).
The Ministry of Forests, Government of the Province of British Columbia, Canada, shared the concern for accelerated harvesting of yew where there was also a sudden, increased pressure on the Taxus brevifolia population due to the discovery of the medicinal properties of taxol. A policy was formulated to "support and promote the orderly harvesting of bark from western yew ." Guidelines for the harvesting of yew bark were designed to facilitate the long-term survival of yew and to maintain its genetic diversity. These provided for yew harvesting in the following areas:
The harvesting of yew needles is administered in the same manner under this policy. Needles may be harvested from 50 percent of the yew trees by diameter class in a clump and no more than 50 percent of the foliage may be removed from any one tree. Current policy does not require harvesters of yew bark or needles to make payments to the Crown for these products. However, if yew logs are removed, the logs must be scaled and stumpage will be charged.
During the late 1980s and early 1990s only bark was collected from Taxus brevifolia for recovery of taxol. Needles could be harvested but there was no current demand and no approved FDA process for extracting taxol from needles. Harvesting of yew bark is done by stripping the bark from live trees. The bark can be stripped from standing trees or from trees that have been recently felled. The bark is stripped from all of the trunk and limbs down to a diameter of about 2.5 cm. Yew bark is harvested in the spring and early summer when there is more available taxol in the bark and the bark is easier to strip. At other times of the year, the lack of fluid in the bark reduces the taxol content and causes the bark to stick to the tree. Yew bark can be harvested as soon as the sap begins to flow in the spring. The stripped bark is packed out by humans, draft animals or, where access is possible, by all-terrain vehicles (USDA Forest Service 1993).
Figure 5.2: A western yew, Taxus brevifolia, is the prime source of the anti-cancer drug taxol.
Figure 5.3: Close-up of the foliage of Taxus brevifolia.
As part of its research and development programme for taxol, BMS aggressively pursued alternative methods for producing this material in order to decrease its dependence on the bark of Taxus brevifolia growing in natural forests. The company recognized that naturally occurring Pacific yew is a finite resource and did not consider it to be a sustainable source for long-term taxol production. Research directions that were pursued included:
In January 1993, BMS announced that, as a result of significant progress
with alternative approaches, the company no longer needed to purchase large
quantities of yew bark from federal forest lands, thus relieving pressure
on a limited forest resource (USDA Forest Service 1993).
Tanning hides with extracts of bark from trees is an ancient technique dating back at least 5 000 years. The oldest evidence of tanning, a tanning yard with tools, pieces of skin and leather, acacia seed pods and fragments of oak bark was discovered by Italian Egyptologist C. Schiaparelli and shows that the Egyptians used a vegetable tanning process similar to that used today. Tanning was depicted in Egyptian tomb paintings dating from 3000 BC and was known to the Chinese as early as in 1000 BC. The Romans tanned with the bark from oak trees. Native Americans used a variety of local plants to make leather from hides of the American bison. The Neolithic people of Europe are believed to have tanned hides by immersing them in water holes filled with bark high in tannin content.
Although tanning is an ancient industry, the actual chemicals that cause
tanning were not discovered until 1790-1800 in France when tannins were
isolated as distinct chemical compounds (Prance and Prance 1993).
The tanning process is possible because of a property of chemicals known as tannins, which allows them to combine with the protein of animal skins, known as collagen, to produce leather. This product is tougher and more permanent than unprocessed (untanned) skins.
Tannins are chemically classified into two groups, the hydrolysable tannins and the condensed or nonhydrolysable tannins. Hydrolysable tannins (gallotannins) are glucosides. They contain a central core of glucose or other polyhydritic alcohol with gallic acid residues attached out from the core. Condensed tannins (polyphenols) are compounds of high molecular weight. They are polyphenolic polymers apparently lacking sugars.
Tannins are acidic and very astringent. This property has made them
an important ingredient of traditional medicines. In addition to the production
of leather, they are used in food processing, fruit ripening and are an
ingredient of many beverages (e.g. cocoa, tea and red wine). When mixed
with iron salts, tannins produce a blue-green colour, which is the basis
for the production of inks. Tannins are also used as mordant in dyes (Prance
and Prance 1993).
Tannins are derived primarily from the bark of trees and are considered to be among the most important products from tree bark. Tannins are widely distributed in the plant kingdom. About 500 plant species in 175 families are known to contain varying amounts of tannins. These compounds are particularly abundant in various species of acacias, Acacia spp., hemlock, Tsuga spp., oaks and related genera, Quercus, Castanea, Lithocarpus, and certain mangrove species.
One of the primary coniferous sources of tannins is the bark of the eastern hemlock, Tsuga canadensis, a tree that is widely distributed across eastern North America. The bark of this tree has a tannin content of about 10-12 percent and was used to tan sheepskins and heavy leather for shoes in the United States during the late nineteenth and early years of the twentieth centuries. The trees were felled and the bark removed in spring with a bark spud when the sap was flowing and the bark was easiest to peel. A four-person barking crew was used for this work and consisted of a spudder, a feller and two "bucklers" who chipped off chunks of bark roughly 1.2 meters in length and 45 cm wide. The bark was then dried and the tannin extracted by open diffusion or percolation (Prance and Prance 1993).
In 1900, 1.2 million cords of hemlock bark was harvested in the United States and accounted for 72 percent of all tannins used. Harvesting operations were carried out over an area of roughly 400 000 ha across eastern United States. About 2.5 cords of bark were required to tan 100 hides. The industry was a destructive one, which ultimately led to extensive deforestation of hemlock forests (Hergbert 1983, Prance and Prance 1993). During the early years of hemlock bark harvesting, the remainder of the trees was not utilized because there was no demand for hemlock lumber. The barked logs were simply left to decay in the forest. Eventually, the logs were marketed as a by-product of the tanning industry.
By the 1930's, hemlock supplied only 18 percent of the raw material for the American tanning industry. As the area of hemlock forest declined, the industry moved further south into the forests of oak and chestnut to draw upon an alternative source of supply. Eventually, the American leather tanning industry relied on importation of tannin from foreign sources or tanning was done by alternative chemical processes (Hall 1971, Hergbert 1983).
The bark of the western hemlock, Tsuga heterophylla, a tree indigenous to the north-western United States and adjoining portions of Canada and Alaska, was used as a source of tannin during the early years of this century but on a relatively small scale. Later, research indicated that the bark of three western North American conifers: T. heterophylla, Pseudotsugamenziesii and Sequoia sempervirens were potentially strong sources of tannin. As a result, some plants were built during the 1950s to supplement supplies of imported tannins. However, most of the product was used as dispersant to control the viscosity of oil well-drilling fluids (Hergbert 1983).
According to a report from Chile, the bark of Pinus radiata contains approximately 10-11 percent tannin. In an attempt to utilize this resource in conjunction with harvest of timber products from the country’s 1.5 million ha of pine plantations, a tannin extraction plant was developed in the VIII Region, in the heart of Chile’s pine plantations. This plant has the capacity to produce 600 tonnes of tannin/year. Unfortunately, the market for Chilean-produced pine tannin is limited and the plant is presently not operating (Garfias Salinas et al. 1995).
In Europe, the bark of Picea abies has been used as a source
of tannin in the leather industry (Hora 1981).
With the exception of the specialized products described in the preceding sections, tree bark was generally considered to be a waste product of the timber industry, which required disposal. This was typically done by burning bark, along with wood residues (sawdust, shavings, wood chips, etc.) in a device commonly known as a "tepee" or "wigwam" burner. These devices frequently caused smoke pollution, especially in the mountain valleys of timber-producing regions where concentrations of sawmills and other wood processing plants are typically located. At one stage, the annual volume of bark requiring disposal in the United States was estimated to be between 7 and 20 million tonnes, while in New Zealand, for example, between 0.25 and 0.50 million tonnes of waste bark were generated annually (Ellis 1973).
During the late 1960s and early 1970s, the need for increased utilization
of tree bark was recognized as a means of reducing volume of waste bark
requiring disposal. This led to the development of a number of new by-products
of the timber industry.
In recent years, oil spills, especially in salt water, have resulted in pollution episodes of disastrous proportions, involving losses of wildlife and fisheries resources as well as damage to beaches, boats, docks, marinas, etc. The ability of bark to absorb oil was first reported in Sweden following an accidental oil spill. Investigations following this discovery measured the amount and rate of oil sorption by various bark particle sizes and species (Fahlvik 1967, Anon 1968). In 1968, the Texas Forest Service Forest Products Laboratory of the Texas State Forest Service began to investigate the capacity of bark from southern yellow pines (Pinus echinata and P. taeda) to absorb accidental oil spills. Initial studies indicated that southern yellow pine bark absorbed up to four times its weight in oil, with the sorption rate dropping off hyperbolically as bark particle size increased. It was also found that the bark itself contributed some pollutants to cold water but these pollutants do not appear serious if bark is properly applied (Martin et al. 1973). A three-step processing of pine bark was subsequently developed which involves breaking bark into small fragments, drying the bark and screening it. Processed bark could be delivered to coastal areas in Texas for about US$ 20-30/tonne. This product could be used with ship mounted booms to act as barriers to oil slicks and to absorb and hold the oil. Oil soaked bark is then retrieved manually with special nets or mechanically by pumps (Weldon 1973).
Effective use of pine bark as a means of containing and absorbing oil spills requires the availability of a huge volume of bark. For example, it was estimated that a spill the size of the Torrey Canyon spill would have required at least 30 000 tonnes of pine bark. This represented a volume equal to total bark production of every pinewood processing plant in Texas for a period of three weeks (Weldon 1973).
Manufacturers in several countries (Finland, Germany and the United States) have developed a process of making particleboard either entirely or partially from bark. As early as 1961, a report from the former German Democratic Republic (East Germany) indicated that 20 000 tonnes of spruce bark were used annually in the manufacture of particleboard. A similar product was produced in the Czech Republic (Hall 1971).
Suggested uses of particleboard made from bark include:
Finely milled, clean softwood bark (Abies, Picea, Pinus, Pseudotsuga) is becoming accepted as a substitute for peat moss as a mulch and soil amendment. The pH of conifer bark is generally around 3.8 -4, which is almost exactly that of peat moss. Bark tends to be more uniform than peat moss, which varies depending on where it is harvested. The nursery industry is becoming a large buyer of pine bark as a substitute for peat moss (Thomas and Schumann 1992).
The soil-less growing media used by the greenhouse industry contains about 10-60 percent conifer bark (Thomas and Schumann 1992).
In the United States, a number of bark products are sold as landscaping materials to conserve soil moisture, reduce weed growth, moderate soil temperature and prevent erosion. Pine mulch consists of fine particles of conifer bark. Pine nuggets or decorative bark consists of pieces of thick "western pine or fir" (Pinus ponderosa or Pseudotsuga menziesii) bark, coarsely subdivided by mechanical means and smoothed and rounded by an abrasive process (Hall 1971). Up to three grades of coarseness are available: small, medium and large. This material is commonly spread across plant beds for decorative purposes and as a means of weed control. A common procedure is to cover plant beds with a heavy grade black plastic, then spread a layer of bark chips over the plastic. This results in an attractive, weed-free landscape. Shredded "cypress" or "western cedar" (Thuja plicata) bark is also sold for the same purpose. This product is also popular for covering walkways in formal gardens. Decorative bark chips are commonly sold in garden shops or plant nurseries in 2-3 cubic foot (56-84 litre) bags and sell for approximately US$3.50-6.00 each. This material can also be purchased in bulk quantities from dealers who sell sand and gravel (Author’s observation).
Silvacon is the trademark of products derived from the bark of Pseudotsuga menziesii by a patented fractionation method. This produces three basic components:
Other uses or potential uses of conifer bark include:
8/. Raffia is a material used in basketry made in Madagascar by cutting
palm leaves before they uncurl, stripping the undersides of the leaves,
drying the strips and splitting them into desired widths (Hart and Hart
9/. Information provided by Dr. M.P. Shiva, Centre of Minor Forest Products, Dehra Dun, India.
10/. Information obtained from Joshua Trees National Monument, USDI, National Park Service, California, USA.
11/. Government of British Columbia, Canada, Ministry of Forests, Ministry Policy Manual - Policy 8.12 -Yew Bark Harvesting and Collection - Special Forest Products dated 1 October 1993.