In this article we will discuss about:- 1. Introduction to Bamboo 2. Biology of Bamboo 3. Properties 4. Utilization 5. Research.
Contents:
- Introduction to Bamboo
- Biology of Bamboo
- Properties of Bamboo
- Utilization of Bamboo
- Research on Bamboo
1. Introduction to Bamboo:
Bamboo plays an essential role in the daily life of millions of people in subtropical and tropical regions. Increased research during the recent years has contributed considerably to the understanding of these important arbore scent grasses as well as to an improved processing for wider uses. The treatise gives an overview on aspects of biology, properties and utilization of bamboos with emphasis on further research directions.
The bamboos form an unique group of giant arborescent grasses. They grow naturally in all continents except Europe. Some species can tolerate temperatures between 40° and 50°C, whereas, others can withstand snow or even temperatures of severe frost. For many centuries bamboos have played an essential role in the daily life of the people in tropical countries. Besides the fields of traditional application, modern processing techniques have considerably extended their usefulness.
Despite increasing research efforts the bamboos have remained somewhat mysterious plants. They still encompass many secrets in their biology, and much more information is required for their silviculture and utilization.
Since the general knowledge about these useful plants appears to be rather limited, the Academy Lecture of the International Academy of Wood Science provides a welcome opportunity to elaborate upon this topic to the Fellows as well as to the participants of the IUFRO Congress, who come mainly from regions, where the comprehension about bamboo is often restricted to their use as plant supports and pointers.
Research on bamboo has increased rapidly in recent years. The various activities, especially in Asian countries, were first strengthened by the creation of a IUFRO Project Group on Bamboo in 1976 at the Congress in Oslo, followed by an IDRC / IUFRO Workshop in Singapore, 1980 (IDRC 1980), a subsequent Conference at the IUFRO Congress in Kyoto, 1981, and an International Workshop in Hangzhouw, 1985 organized by the Chinese Academy of Forestry and IDRC, in cooperation with IUFRO (IDRC 1986).
2. Biology of Bamboo:
(a) Identification and Taxonomy:
The number of hitherto described bamboo taxa varies greatly. According to MeClure (1966) bamboos can be classified into 63 genera with about 700 species. A reliable identification is a necessity also for silviculture and utilization. Most identification keys are based on floral characters; bamboos, however, usually flower only once, namely at the end of their lifespan of about 20 to 40 years.
Therefore, vegetative structures have also been considered as possible criteria for classification. Anatomical characters such as epidermal features, arrangement of the vascular bundles, structures of bud-sheaths and leaves as well as the much documented morphology of the culm (size, colour, internodal length, branching) are of diagnostic value.
Attempts have also been made to ‘characterize bamboo species by the gel electrophoretic pattern of proteins and peroxidase isozymes. At a later stage these criteria could well be utilized for identification purposes. Research has to be intensified with the aim of establishing a taxonomic monograph for the taxa of at least one region.
For scientific investigations, collections of all species are necessary, and in several countries impressive bamboreta have been established. A more difficult approach is the centralized storage of germplasm, which is done in Bangladesh in a pioneering way.
(b) Growth Habits:
Bamboo grows in two distinctly different forms due to the types of its subterranean rhizome, i.e. either single stemmed (leptomorph) or densely clumped (pachymorph). The clump type is common in Western Asia; the other type is more in the Eastern warm-temperate and temperate regions, including up-to Japan. Bamboos are the fastest growing plants.
They reach their full height of 15-30 (35) m within a period of 2 to 4 months by diurnal growth rates of about 20 cm up-to 100 cm. Taking also into account their diameter of 5-15 (30) cm, an enormous biomass must be mobilized from the stored energy in the rhizomes within a short time; the growing culm itself hardly possesses enough leaves for producing carbohydrates by assimilation. The storage, mobilization and transport of this energy in the roots is still an untouched field of research.
Studies on the growth of Phyllostachys edulis have revealed the sequence of internodal elongation and the formation of the new nodes. Transport of water and nutrients within the elongating culm and the role of the nodes urgently need investigation.
When the culm has reached its final height and the culm sheats have dropped, the typical colour appears dull and the culm is called “immature”. Later on, it becomes greenish and often yellowish as signs of ageing and maturity. Only the latter culms are harvested, but “maturity” of a culm is a relative term. Even after completion of elongation, carbohydrates appear to be transformed into cell wall material and are deposited.
Evidence from chemical and technological tests regarding the beginning of maturity is quite contradictory. Research on the maturation of the culms will be necessary also to obtain information about the stage when a culm has reached its ultimate strength. Nevertheless, the freshly ripened culms are not harvested since the assimilation products of the young and most vital ones serve for the nourishment of the rhizome and for further sprouting.
Not much information exists about the lifetime of an individual bamboo culm. Obviously, a certain ageing occurs, but hardly anything is known about the physiological and biochemical processes involved in the necrosis. Bamboo culms can live for several decades.
Unlike the dicots, their structural systems for the conduction of water in the xylem and for the carbohydrates in the phloem cannot be replaced by new tissue, arising from cambial activity, but have to function throughout the entire lifetime of, the culm.
Dicotyledonous trees may deposit residues of their metabolism in central parts of their stem or also in the bark, but bamboo has to possess other pathways for the removal of their remnants. Research should clarify the ageing processes of the tissues for transportation (xylem and phloem) and for storage (parenchyma) in the culm.
Most bamboo species exhibit polymorphism with a spectrum of appearance. Side branches, for example, are useful for making fences, but not wanted for culm production purpose. Detailed studies about the morphological variation are therefore useful for selection and utilization.
(c) Flowering:
Most bamboos flower only once in their life. Flowering occurs often gregariously in lengthy and irregular cycles of 30 to 40 or more years. It is one of the mysteries about bamboo at this stage that nearly all culms and clumps of one species start to flower at the same time, irrespective of their age and their distribution over large areas, even over 1,000 km apart from each other.
Thus, from an economic point of view, bamboo flowering and fruiting is something of calamity, since the culms and rootstocks degrade afterwards rather quickly and are no longer available for the rural and urban population and the pulp industry or for the pandas in China. Consequently, intensive research has focused on the reasons for the sudden and quite unpredictable simultaneous flowering of the’ solitary bamboo species.
There are several theories and indications, but so far, no definite cause has been established. The involvement of plant physiologists and biochemists is required for explaining, predicting or even preventing or inducing the flowering of bamboo.
Flowering and subsequent super abundant fruiting consumes all energy reserves stored in the parenchyma cells of the culm and rhizome. This may contribute to their death soon after. As a minimal advantage, the depletion of starch makes the culms nearly resistant against the most common bamboo beetles, which belong to the Dinoderus group.
But also more severe changes seem to occur in the tissues since the dead culms are often bent down, become brittle and break. Are there changes in the chemical constitution of the tissues or the lignified cell wall? Apparently, not much is known about such alterations. Research into the phenomena of this rapid decline is highly desirable – not only from a scientific point of view but especially with respect to the utilization and conservation of the large amount of material suddenly available.
(d) Silviculture:
Only a-few aspects of bamboo silviculture can be mentioned here.
Propagation:
The propagation of bamboo is necessary for any afforestation or reforestation and for local planting by the villagers.
Propagation by seed is the best method, although, seeding cycles occur only at lengthy intervals. Seeds have a limited period of germination, usually only a few months. Nevertheless, Dictrich Brandis, the Father of Indian Forestry, could introduce several bamboo species around 1900 to Tanzania with, seeds from India.
Basic studies on seed biology should be undertaken with a view of prolonging their viability.
Vegetative propagation by cuttings from culm, branches or rhizome is commonly practiced. So far, several methods are applied but for practical purposes the degree of failure is still rather high. Universally applicable methods for vegetative propagation of bamboo are not yet available.
Therefore, research is presently undertaken with the primordial structure of buds and especially with tissue culture for mass propagation and germplasm exchange. The results are promising when using the vegetative or leaf tissue for callus formation and further organ differentiation to obtain plantlets.
The sporadic flowering is occasionally used in hybridization experiments for gaining data about genealocal classification and for utilizing the beterosis effect.
Volume and yield are important criteria for the cultivation of bamboo. The biomass above ground has been calculated for some species as being between 50 and 100 tons/ha. There are considerable differences in yield depending on species and growth conditions.
The sustained yield may generally be assumed to amount to 5- 12 tons air-dry material/ha from plantations, with higher yields on good soils aided by proper management and by the use of fertilizers. Provenance and growth trials have been intensified or started respectively, in several countries. More research is needed for the various species on the influence of different stand management practices, such as density, felling cycles and the use of fertilizers. Chemical fertilization can increase the yield by more than 50%; the possible influences on the structural properties should be investigated.
These few comments may indicate some of the many research needs for the silviculture of bamboo. Furthermore, studies on pests, diseases and injuries, as well as on harvesting and transport are necessary.
3. Properties of Bamboo:
Considerable research has been done during the last decade on the properties of bamboo.
Anatomy and Fine Structure:
The properties of a culm are mainly determined by its anatomy and fine structure. The total culm comprises about 50% parenchyma, 40% fibres and 10% conducting tissue (vessels and sieve tubes). There are some variations according to species, but more striking is the definite distribution pattern within one culm, both horizontally and vertically.
The percentage of fibres is distinctly higher in the outer third of the wall and in the upper part of the culm contributing to its superior slenderness. Xylem and phloem are arranged in vascular bundles and surrounded by parenchyma.
The parenchyma cells, forming the basal matrix, are mostly elongated with interspersed shorter cube-like cells. The longer ones are characterized by thicker walls with a crossed polylammellate structure. Apparently, they become lignified at early stages of shoot growth.
The shorter cells have a denser cytoplasm and thinner walls; they retain their cytoplasmic and strong peroxidase activities for a long time. The function of these two different types of parenchyma cells and their role in the storage and mobilization of carbohydrates is entirely unknown at present.
Another striking feature is the occurrence of warts in the elongated parenchyma cells. Warts on the walls of tracheids, fibres and vessels of dicots are well known, but they are not seen in the parenchyma. In the bamboos, warts occur in fibres and vessels as well in parenchyma, but not regularly within all three cell types in all species.
The warts in the parenchyma are clearly distinguishable from cytoplasmic debris by their dark contrast in lignin skeletons, indicating a high lignin content. The elongated parenchyma cells contain much lignin in their walls, whereas, the parenchyma of dicots without warts have a purely cellulosic wall. Thus, the lignification process may be a prerequisite for the development of warts. Further research on the presence, formation and distribution of warts in bamboo appears worthwhile.
The fibres constitute the sclerenchymatous tissue and occur in transverse sections in the form of caps of the vascular bundles or as isolated longitudinal strands. Their length, varying between 1.5 and 4.5 mm, is of interest especially for the pulp industry. There is a considerable variation between species, but distinct patterns also exist within one culm with a maximum at the middle part of an internode.
Most of the fibres have a thick polylamellate secondary wall. The lamellation consists of alternating broad and narrow layers with different fibril orientation. The broad lamellae are oriented at a small angle to the fibre axis; they possess a lower lignin content than the smaller lamellae with a transverse orientation. ‘The typical tertiary wall, as known from woody cells of gymnosperms and dicotyledonous angiosperms, is not present.
Beside the polylamellate fibres there are others, which do not show such lamellation. Not much is known about these differences.
Septate fibres have frequently been observed in several hom-boo species. In addition to the original septum, these fibres possess variable numbers of lignified secondary wall lamellae on both sides attached to the original S2-layer. Such a septal structure is quite different from that generally known in angiosperms, where the septa reveal no secondary wall component. They generally remain thin and unlignified.
4. Utilization of Bamboo:
From the vast field of bamboo utilization a few examples may be presented.
(a) About the Shoots:
Bamboo shoots are an important daily food for many people in Asia. Different countries prefer different edible species, some species such as Dendrocalamus giganteus can be eaten even raw, while others contain lethal amounts of cyanogen, which are destroyed only by cooking. Since the nutrient composition decreases with age an early gathering – when the shoots are still underground with the sheaths just appearing — yields higher quality in terms of sugar, protein, fat, free amino acids, vitamins etc. Results are taste test are still meagre. The nutritional composition of the various species and changes due to external influences, such as fertilization, are still to be investigated in a more systematic way.
In Tanzania, growing shoots of Oxytenanthera braunii are decapitated, and the extruding sap can be collected for many weeks. The sap ferments within 2 days into a quite tasteful drink called Ulanzi. Why can the sap be collected apparently only from this single species and what mechanisms make it flow over a long period, up-to several months?
(b) About the Plant:
Living bamboos form an essential feature of oriental gardens, and species with a colorful appearance or bizarre habit are preferred. For example, the tortoise-shell bamboo, a degeneration of the common Phlyllostachys edtilis var. heterocycla, has greatly reduced internodes with a zigzag arrangement of the nodes. Such culms are produced together with normal ones from one rhizome, but the causes for the irregularity are unknown. Vessels and sieve tubes contain numerous inclusions already in the first year. The possible interrelation between these occlusions and the anomalous growth merits further efforts.
(c) As Building Material:
Bamboo is an indispensable material for construction. Besides its traditional applications in the round or split form, modern technologies are utilizing this light, inexpensive and most flexible material for houses and other constructions.
The use of bamboo for trusses has been explored and different forms of joints have been designed. In such constructions bamboo will hardly break and may even regain its original form when the load is removed. More attention should be given to the design details in buildings and also to improved durability.
Research especially in India and the Philippines, has proved the suitability of bamboo as a concrete reinforcement. The load carrying capacity of structural members can thus be increased considerably. In order to avoid a chemical weakening of the bamboo splints they should be boiled in an asphalt emulsion and then covered with coarse sand to provide a better contact with the rough surface.
(d) Processed Bamboo Products:
The unique properties and the beauty of bamboo are improved by modern processing techniques, transforming the raw material into high quality products. Only a few items will be mentioned. Presteaming facilitates bending to reduce internal stresses, and microwave beating has also been successfully applied. Laminated bamboo, glu-lam or “lamboo”, has been developed as a structural and decorative material in a variety of styles.
Bamboo is also peeled and processed into ply-bamboo with various adhesives. Such material was already produced in China during World War II for aircraft construction. The use of such bamboo products as supports between sleeper and rail demonstrates the strength quality and weather resistance of bamboo.
The manufacture of hardboards and particle boards should be further explored. Building boards from woven bamboo mats with saw-dust or coconut coir pith as fillers reduce the shortage of wood for such purposes. New processing techniques and machines will further improve the quality and usefulness of bamboo-based products.
The significance of bamboo for pulp and paper can only he mentioned. About 7.8 million tons of raw bamboos are consumed annually, but only some species have been accepted by the industry. The reasons for the neglect of certain species should be known better, because pulp and paper from bamboo are of great importance for some countries. Chemical processing offers considerable potentials. Charcoal, tar, vinegar are traditional products from dry distillation, but diversified products will be obtained following intensified research.
As one recent promising example, the steam explosion process should he mentioned. By this method, bamboo chips are treated with saturated steam at 28 kg/cm2 at about 230°C and converted by Trichoderma cellulose into an easily hydrolysable material, which can be used for cattle feed. In Brazil, work is in progress on a combined production of paper together with starch as a food product.
Research on bamboo is a vital field of science. The abundance of this valuable raw material in certain regions requires further efforts. It is an aim of this survey to increase interest in and to stimulate research on bamboo among Fellows of the Academy of Wood Science and Technology.
Uses of Bamboo:
Bamboos are poor mans, Timber and rich mans, luxury.
It has Various Uses:
(a) Fodder:
Leaves and tender shoot are relished by cattle.
(b) Medicinal:
Dendrocalamus species yield siliceous secretion at the base of female plants-known as “Banslochan” (Tabashir) is used by traditional medical practioners as stimulant and aphrodisiac. Leaves are used as emenagogue and anthelmintic. Roots as diluent. Dried culms as splints in surgery also as decoction for cough and cold.
(c) Shelter:
All bamboos are used for making hutments, cheap roofing material.
(d) Containers:
Variety of containers and Baskets from all Bamboo called Chhatoni, Kandu, Meretha, Chapri etc. These Baskets are masterpieces of rural arts and craft used as decorative pieces.
(e) Food:
Young shoots, Buds and tuberous basal stock used as vegetables and pickles.
(f) Rituals:
In rituals, Bows, Arrows.
Bamboos are also used for making flutes, musical instruments, Umbrella handles, Frames of cots, Walking sticks, Lathi, Ladders, Scaffolding handy gadgets, suppa, Water floor-mills, Fishing rods. Long fibre pulp wood for paper and pulp industries.
Bamboo has been man’s companion throughout life in one form or other right from birth to his grave.
Bamboos are very good species to be raised in Agro-forestry as source of additional income.
5. Research on Bamboo:
Fibres and tracheids in hardwoods and softwoods may form a reaction tissue in curved parts of the tree. Bamboo fibres, however, apparently do not develop such an abnormity comparable to tension of compression woods. Most monocots so far studied, such as Cocos and Rattan palms, also lack reaction wood. One exception is Xanthorrhoea australis. In straight culms of a bamboo, however, fibres with gelatinous layers may occur, similar to those in tension wood. It might be of interest to further investigate the formation and occurrence of such partly lignified tissue.
The fibres are grouped in the shape of cups and bundles around the vessels. The arrangement is quite characteristic for the various species. Distinct patterns can be distinguished mainly due to the-presence and location of one or two isolated fibre bundles in addition to the central vascular strand with only sclerenchyma sheaths as supporting tissue. This appearance of the vascular bundles has taxonomic significance. Further investigations on the types of vascular bundles as well as on their variation and significance appear worthwhile.
The conducting xylem in the vascular bundles of the culm consists of one or two small protoxylem and two large metaxylem vessels. The protoxylem mostly has annual thickenings. These are already formed, apparently from an initial septum, when the surrounding cells are still parenchymatous before becoming fibres.
The thickenings are connected in the early stages by membranes as an extension of the original primary wall which raptures during the extension growth. Later they are completely separated from each other and come to lie loosely in the protoxylem lacuna.
The metaxylem vessels have a secondary wall with two distinct parts equal to the S1 and S2 layers, with microlamellae present. In some species they possess a polylamellar structure with up-to 5 narrow and broad lamellae in alternate arrangements, partly, producing-herringbone pattern. The pit membranes towards the surrounding lignified parenchyma cells reveal a uniform structural principle with microfibrils grouped in a random pattern. No incrustations by matrix substances have been observed normally, but it would be worthwhile to investigate older culms.
The perforation of the metaxylem vessel is simple with rims either horizontally or slightly oblique. In Sasa-bamboo scalariform perforations have been observed occasionally. Rarely a new type of multiple perforations has been found. It forms a fringelike perforation and may be caused by a disturbance of the differentiation process, since it was observed in a curved internode (D. strictus).
Finally, the phloem should be briefly mentioned. It consists of large thin-walled sieve tubes with small companion cells, which exhibit known cytoplasmic organization with well-developed cuneate clectrondense inclusions in the plastids.
These proteinaceous bodies are combined with several tiny crystallizes of the lattice nature. Starch grains have not been observed in the sieve tubes of the culm even in late stages. Since the sieve elements have to function during the entire life time of a culm, unlike those of the dicots, changes during ageing are of special interest.
The formation of a vacuole has been observed restricting the cytoplasm to the periphery. Sometimes, a blocking of sieve tubes by tylosoid-like outgrowths occur, whereas the companion cells become sclerified. Tyloses have been seen only in the intercellular space of monopodially growing taxa.
The epidermis of the culm shows structural variations as in the case of leaves, which can be taxonomic significance. The epidermal wall consists of an outer and inner layer; the latter appears to be highly lignified. The cutinized layer is composed of cellulose and pectin and has a tangential lamellation. A wax layer is formed on top. Frequently, silica particles are incorporated in peripheral parts of the culm tissue.
The comments on the structure refer only to the internodes, whereas the anatomical structure becomes highly modified and complex in the nodes. Here the vascular bundles and the phloem become extensively branched and rearranged. Investigations on functional structure of the nodes would constitute a fascinating research topic.
(a) Chemical Properties:
Bamboo consists of about 50-70% holocellulose, 30% pentosans and 20-25% lignin, with some variation according to species and age of the culm. Since the culm completes its maturation within about one year, the associated changes in carbohydrates and lignin are of interest. Certain modifications associated with further ageing have been noted, but more insight into the chemical composition, including conditions of growth are needed. Such knowledge will provide avenues for their potential utilization, including pharmaceutical possibilities. The chemical composition may also give information for taxonomical identification and seed selection.
More than 90% of the bamboo hemicelluloses consist of a xylem, which has a unique structure within the family of Gramineae and is an intermediate between hardwood and softwood xylems. Bamboo possesses a typical Gramineae lignin which is built up by the three phenylpropane units, p-cournaryl, coniferyl and sinapyl alcohols. The lignification process during the elongation of the growing culm shows various stages from the bottom to the top of a culm; further investigations would be welcome.
Not enough is known about the location of the silica which amounts to 0.5 to 4% of the culm and affects its pulping quality. Besides the leaves most silica appears to be deposited in the epidermis, whereas the internodes and nodes contain none or little.
(b) Physical and Mechanical Properties:
The density of bamboo varies between 0.5 and 0.8 (0.9) g/cm3 (oven-dry weight).
It depends mainly on the size, quantity, and distribution of the fibre agglomerates around the vascular bundles. Accordingly, it increases from the central to the peripheral parts of the culm and from the bottom to the top.
With decreasing thickness of the culm wall, an increase in specific gravity and mechanical strength especially of the inner parts takes place. Whereas the outer parts these features change only slightly. Bamboo has excellent mechanical properties, especially a superior tensile strength. Several investigations have been undertaken to study these properties, but the information available is far from being sufficient.
Many more of the important species have to be analyzed. Quite contradictory results concerning the influence of age in green and dry conditions have been obtained. Comprehensive tests by Zhou (1981) revealed an increase in strength properties up-to 6 years for tensile and compressive strength and up-to 8 years for bending strength with a decrease in all strength properties in older culms.
The reason for such changes, especially for the apparent drop in strength should be clarified. So far, no standard methods for evaluating the strength properties of bamboo exist, and the available results are based on different methods of testing and on widely varying dimensions.
To conclude this short treatise on the mechanical properties the need for more investigations on the relationship between strength and anatomical characteristics of mature culms must he emphasized. It should be understood why, by experience, only certain species are employed for certain uses.
Some species are easy to split, whereas others are used because of their compression strength or are preferred for carving. The Fibre length appears to be correlated with the modulus of elasticity and with compression strength, but an equal distribution of vascular bundles favours easy splitting. Maximum crushing strength in the top area may be due to the decreased lumen diameter and thicker walls. For splitting and peeling, not only the species but also the age of the culm has an influence.
(c) Seasoning:
The moisture content of bamboo culms varies according to season, but also between species and within one culm. Unlike wood, bamboo begins to shrink from the very beginning of drying. This does not continue regularly but stops around 40% moisture content and may start again below that point. Bamboo tissue shrinks mainly in the radial direction. Compared with timber of the same specific gravity, the drying period needed for air or kiln drying is longer due to the higher initial moisture, content and the presence of water soluble extractives in the parenchyma.
The various bamboo species exhibit a different seasoning behaviour, which is partly attributed to culm wall thickness. Several defects may occur during seasoning, especially surface cracks and collapse. Thick walled bamboo is especially liable to crack. More research is needed on the relationships between fibre saturation point, specific gravity and shrinkage in relation to the anatomical structure of the species. Suitable measures to minimize collapse and splitting during seasoning should also be studied.
(D) Natural Resistance:
The natural resistance of bamboo against insects and fungal attack is rather low and this has to be regarded as a major shortcoming. Water absorption of dried bamboo is quite rapid due to the hygroscopicity of the extractives in the parenchyma cells. Surprisingly few tests have been made concerning the durability of the various species against deteriorating insects and fungi in the field and under controlled laboratory conditions.
Likewise the mode of fungal attack on this heterogeneous cell tissue remains to be analyzed. Field observations and practical experience indicate differences between species, such as in the Philippines with Dendrocalamus meerillianus as perishable and Schizostachyum zollingerii as quite resistant.
Nothing is known so far about the presence of any compounds, which could influence the durability, except starch, which can be plentiful making the culms highly susceptible. Again, more systematic research is needed. Besides its low durability bamboo is refractory towards impregnation, but the relevant problems cannot be outlined here.