WBC-VIII-Vol.4 – Resources – Forestry, Plantations and ... - BambuSC

of average forest tree stands (100–160 t/ha), but does not match that of the very high values attained by some
tree stands (300–1,700 t/ha; Hunter and Wu 2002). In contrast to trees that can accumulate biomass over long
periods through radial and vertical extension of stems (trunks), bamboo culms lay down most of their biomass
within their first year of growth, largely from current assimilation but also from redistribution from older culms
and rhizomes (Magel et al. 2006), and die off after a maximum of 8–10 years, resulting in a decline in biomass
of individual culms over long periods. Isagi (1994) referred to this as the biomass accumulation ratio
(biomass/net annual production) and showed it to be 4.66 for a stand of Phyllostachys bambusoides in Japan.
Culms on average comprise c. 75-83% of total aboveground biomass, branches c. 12-15% and leaves c. 5-7%.
On an annual basis, above-ground culm growth rates (fresh weight) of 10–30 t/ha/year have been reported
(summarised by Kleinhenz and Midmore 2001), which is in line with those of woody species (Hunter and Wu
2002). Although one report with Bambusa bambos mentions 47 t/ha/year, productivity of bamboo on an annual
basis is generally no greater than that of woody species, and bamboo is no more efficient at sequestering carbon
than are woody species. Below the ground, bamboo sequesters carbon in the form of rhizomes, and belowground
biomass is greater proportionately for monopodial (running) species at c. 43% of total biomass compared
to c. 31% for sympodial (clumping) species (Kleinhenz and Midmore 2001). The rhizome therefore represents
an important sink for sequestered carbon but, according to Hunter and Wu (2002), this sink is no larger than that
of woody trees. One advantage of bamboo over trees is that culms can be harvested much sooner than trunks of
woody species (Figure 1) and another is that they can be harvested on an annual basis without the environmental
consequences of clear-fell. Given that culms can be harvested on an annual basis, inter-culm competition for
light is lessened, and younger culms, those with greater photosynthetic efficiency, gain greater access to light,
supporting therefore faster growth rates. This is evident in Zhu et al. (2009) who show the drop in light
interception by the canopy when older culms are harvested and the capture of that light by younger culms soon
thereafter. The effect on biomass is marked. For example, net annual biomass production of 9.3 t/ha per year in
12-15 year old Dendrocalamus asper was raised to 26.3 t/ha per year one year after culms >4 years of age were
removed from the clumps (Kao and Chang, 1989).
Removal of all culms at harvest represents removal of c. 150 kg N, 30 kg P and 260 kg K per hectare, leaving
between 25 to 70% of those amounts in the rhizomes (Kleinhenz and Midmore 2001). Exceptionally, higher
values up to five times these have been reported. On an annual basis, with culm yields of on average 13 t/ha/yr c
36 kg N, 9 kg P and 63 kg K are removed per hectare, but with culm yields possibly four times these values
much more would be removed.
Leaf litter annually provides between 13-22% of the total NPK in total biomass, when stands are 6 years or
older, and some is taken up for incorporation into new leaves which are the major sinks for nutrients. The
resorption efficiency is higher for K (c. 43%) less for P (37%) and least for N (19%) (Embaye et al. 2005).
Internal recycling is important for bamboo to make efficient use of nutrients, as is the ability to take up nutrients
from a decomposing litter mass (Das and Chaturvedi, 2006). Nevertheless, without nutrient inputs the soil
nutrient resource declines, as illustrated by data of Wu et al. (2006) showing that total soil N decreased by 5.2%
and available P by 15% following 3 years continuous cropping with Phyllostachys iridescens.
VIII World Bamboo Congress Proceedings Vol 4-71