**4.1. Biomass growth: aerial and root system characteristics**

Bamboo belongs to the grass family and has an aerial part characterized by a jointed stem called a culm. The culms are typically hollow with the exception of certain bamboo species which have solid culms. Each culm segment begins and ends with a solid joint called a node. It is in these nodes that the vegetative parts of the culm able to develop the culm vertically, produce branches and develop roots and stems if stacked or laying in the ground can be found. The underground part of the plant is built from rhizomes growing normally at a shallow depth (up to a maximum of 150 mm) from where the roots develop. These roots can grow deep into the soil up to 500 mm. The rhizomes are the main form of spreading of the plant by growing horizontally away from the plant and, because they have a similar structure as the culm with vegetative nodes developing either roots or buds, originate new shoots and new individuals.

Bamboo is the fastest growing perennial, evergreen, arborescent plant with a resulting high productivity: the dry weight yield per hectare could total as much as 32–38 or even 47 tons of biomass per hectare per year but averaging 8–18 tons per ha per year in normal conditions according to the different species and locations [8].

This productivity, expressed both for the aerial and the root parts of the plant, illustrates the ability of bamboo to cover the terrain very rapidly, to develop a dense network of subsuperficial rhizome and root system which would structure and consolidate the upper soil layer. The growth rate of each plant varies, but there are references of a 900 mm culm elongation in 1 day. The growth rate (both of the culm, the rhizome and root system, buds and shots) corresponds to a vegetative cycle that varies with the species and the climatic conditions. The growth factors (like starch reserves on the culm and the rhizome) vary with the evolution of the growth season but are maximal before sprouting, meaning a high resilience to disturbance and regeneration ability. The biomass production is very intensive both above and below ground with values of above ground dry weight varying between 0.8 and 1 tons per ha in some references [9].

The bamboo stands act as an important factor in water and nutrient conservation, as well as soil protection and runoff control. There are references of reduction in nutrient loss higher than 50% and similar values for runoff retention. This shows that bamboo stands, although having little geotechnical ability in terms of slope stabilization (due to the low depth of rooting), could have a very important role in local water cycle regulation and, therefore, soil consolidation and stabilization, preventing erosion and reducing infiltration [10].
