Bamboo: a fascinating plant.
Excerpt from the Thesis published in Venice in July 1997 under the title The Bionics of Bamboo. Author dr. arch. Giovanna Barbaro .
English translation and adaptation by Mario Rosato, Barcelona January 2009.

Introduction

This research and experimentation thesis, published more than a decade ago in Italy, has been motivated by a curious question: Why has Nature perfected over the course of evolution plants like bamboo, with a stem neither completely hollow nor completely solid?

One possible answer among many, because Nature is so complex that needs to be studied deeply with dedication and especially by multidisciplinary teams, can be articulated into three sections.

The first is the result of a systematic research on bamboos from the botanical point of view and with regard to their physical and mechanical properties, the second is a historical overview of the technologies in processing raw materials, on the wide use of these plants in their Countries of origin in various sectors like building and home accessories ; and last a valuation made in the Laboratory for Testing of Materials of the University of Architecture of Venice on the contribution of the nodes to the overall resistance of a bamboo pole subject to critical load and bending.

The Author has updated some excerpts to share with the Readers the most fascinating aspects of this plant, which in Europe is still undervalued, despite its excellent potential for the sustainable development of our model of society.

Botanical features and origin.

Bamboo is the common name, of Indian origin, applied to all tree-like plants with woody trunk and shape of cane. The Genus of the family Monocotyledons include grasses, which in turn includes the subfamily of bamboos. From the systematic viewpoint of the grass tribe (subfamily) Bambusae is subdivided into five subtribes: Dendrocalaminae, Melocanninae, Bambusinae, Arundinaceae and Puellinae.
Botanical literature gives very different information on the number of families and species of bamboo. Lübke, 1967, points out about 500, the American Bamboo Society some 470 of which 400 grown in USA. Summing up, we can highlight two major groups based on the type of rootstock and the growth characteristics of the reeds: the monopodial bamboos (picture below by Shinji Takama, Die Wunderbare Welt des Bambus, Ed Dumont)



and the sympodial bamboos (picture below of Noah Bell, 2007, www.shweeashbamboo.com).


In the first ones, rhizomes form long and thin extensions of the reeds which grow at regular intervals. The latter have short and thick bulbous roots, which ends produce the canes.

In the Old World bamboos grow from 32 ° S (South Africa) to 46 ° N (Kuril Islands). In the New World, they are found from 47 ° S (Patagonia, Argentina) to 40 ° N (Philadelphia, USA). 65% of known species are found in India, Burma and Indonesia. In Europe, the bamboo was introduced in 1855 in France, with a plantation of 6 hectares in the locality of Générargues.

The astonishing biology of bamboo and its dissemination.

Bamboo grows best in tropical or subtropical climates, however there are species that tolerate up to -25 ° C as Chusquea aristata, which grows in Ecuador up to the line of perennial snow of the Andes.

Monopodial species spread horizontally from 1 to 6 m / year, for about 10 years, whereas sympodial species spread horizontally over short distances, according to a radial pattern in which each bulb generates another 2 or 3. Different root systems can intersect, forming networks of progressive scale ranging from 25,000 to 187,000 km / ha and thus effectively contrasting soil erosion, particularly in areas most prone to crumble and break, and along embankments and river banks. Monopodial.

The buds develop from the rhizome and can remain underground for several years. Just emerging, they grow with great speed: within 20 - 30 days the cane reaches its maximum height, and from then it strengthens. Depending on the species, the cane can not grow more than 30 cm in height with a maximum diameter of 2.5 cm or in certain conditions reach 40 m in height with diameters of 5 to 12 cm and thickness of the wall of the trunk 1 cm. Except for grass, no other plant grows as fast as bamboo, with a record of 121 cm / day measured in 1956 by Nagaoka in Kyoto in a specimen of Phyllostachys edulis.

Normal growth is 25 cm / day and every shoot that sprouts contains in miniature all the nodes that the mature cane will have.

The high growth rate of bamboo results in a high productivity of biomass that, under ideal conditions, can exceed 50 tons / ha / year.

Because it is harvested 5 years after having been planted and regenerates without having to replant it, the bamboo contributes to sustainable forest management.

One of the most mysterious aspects of bamboo is its flowering.
Some species die after having fruited, while others can bloom several times annually. Small species bloom at intervals of 3 or 4 years, while giant species do after a period of 20 to 120 years. Flowering can be sporadic or mass, i.e., only a few rods around the root ball or individual, or even all bamboos in one nation. In 1880 some rhizomes of Chusquea abetifolia from the West Indies were planted in a greenhouse in England. In 1884 the canes bloomed in the greenhouse at the same time as their sisters in the area of origin. It seems that there is a correlation between the flowering of bamboo and the activity of sunspots.

The flowers give rise to fruits, which generally fall to the ground before ripening. The seeds have a low fertility rate: during an experiment conducted in 1966 by Mc Clure, only 1% of seeds planted germinated. Normally the plant dies along with its rhizomes some weeks after having produced the fruits.

If the biological aspects of bamboo are amazing, its mechanical properties are a source of inspiration for biomimetics experts. Observing for example the distribution of the vascular vessels in the wall of the cane, it is evident that the fibers of higher strength are more densely grouped at the periphery, where static efforts are higher, in a similar way to the armor bars of reinforced concrete buildings.

According to Stockel, the resistance to traction of the fibers that run parallel to the axis of the reed reaches 4000 kg/cm2. To understand the magnitude of this figure, remember that timber does not exceed 500 kg/cm2, construction steel Fe B38K resists until 3750 kg/cm2 and fiberglass reach 7000 kg/cm2.

The bark of the bamboo has a high silicon content, which gives interesting properties of fire resistance.
The first tests on fire resistance back to the 80s of last century and were made by the Institut für leichte Flächentragwerke, University of Stuttgart – Germany, where bamboo is certified as a flame retardant combustible material. In Spain bamboo meets the standards of the new CTE (Technical Building Code) and the tests of fire resistance according to the Norm UNE EN 13501 classify this material as category CFL-S1 , hence suitable even for public buildings.

The versatility of bamboo is a solution for sustainable development. Nowadays it is often spoken about the problems derived from the unsustainable management of the environment, such as the rising temperatures and sea levels, with the consequent unbalances in different ecosystems. Life in metropolitan areas is becoming harder by lack of air quality, while environmental technicians prospect threatening short-term scenarios because of water shortage and biodiversity reduction. Albert Einstein said "If the bees begin to disappear, mankind would be left a few years of life."

In the immediate future, major interventions, both of professionals and of any human being, should be addressed to protect the biodiversity of both plants and animals. If we want to deliver our planet livable to future generations, we must control the growth of non-renewable energy consumption by avoiding unnecessary waste and inefficient systems.

The uncontrolled exploitation of timber is directly involved in climate change and is reflected in a devastating hydrogeological instability of the soil and the increase of carbon dioxide with serious consequences of global warming. Personally, as an architect and naturalist, I believe each of us should contribute with his/her own knowledge and ethics to revert or at least stop this trend, beginning by changing our attitudes and lifestyle.

Bamboo is the only alternative to wood because its 100% sustainable farming helps to protect biodiversity and its industrialization process is organic.

If compared to the pine, a hectare of bamboo can provide 2 to 5 times more raw material for the production of paper, fiber boards, tables, charcoal and even wood with a density higher than 1000 kg/m3 therefore very resistant to heel marks. Bamboo’s dense network of roots is an excellent stabilizer of slopes against erosion, and their fronds create an ideal habitat for microfauna. Its rapid growth makes bamboo ideal as a biofilter for phytodepuration of polluted waters and the capture of large quantities of atmospheric CO2. Bamboo’s elegant forms and their ease of cultivation in a wide variety of climates and soils make it a beautifier element in any garden, even during the gray winters.