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

Culm thinning practice
The intensity with which culms are removed from clumps, and reciprocally the number remaining, and the
choice of culms harvested, governs the age structure of culms within a clump. To maximise early capture of
light energy, some recommend leaving all culms in a clump until 4 years after planting (e.g., for D. asper –
Thanarak 1996). It has become clear that for high yields of shoots to be harvested as a vegetable a bamboo stand
should contain a high number of young culms (ideally only 1 or 2 years of age at the time of the shoot season).
Older culms do not support nearly as many shoots per culm as do young culms (Malab et al. 2009). Indeed, in a
high rainfall site in the NT of Australia, shoots selected for culm production at the beginning of the shoot season
themselves produced edible shoots near the end of the same shoot season (Traynor and Midmore 2009). In a
drier environment of Queensland, shoot production was greater when all early shoots were removed for sale,
leaving only late-season shoots for culm production—possibly minimising the effect of apical dominance that
may inhibit later shoot emergence. Likewise in the Philippine treatments with more young culms raised the
productivity index (the number of shoots produced per standing culm – Malab et al. 2009), and in a rainfed site
of Bukidnon, the standing culm density (SCD) of 10-10 (ten 1-year-old and ten 2-year-old culms) gave more
shoots than the 6-6 treatment (Decipulo et al. 2009).
To be sustainable, the number of culms left to support the next year’s shoot harvest must match the number of
culms to be harvested on an annual basis – the duration (or lifespan) of culms between shooting and their
harvest will depend upon the optimal total number to achieve full canopy cover and capture of light energy. For
example, if 15 culms per clump represent the optimal number for such light capture, a clump could equally
contain 5 one year old culms, 5 two year old and 5 three year old culms (a total of 15 culms at the time of shoot
harvest) or 3 one year old culms, 3 two year, 3 three year, 3 four year and 3 five year old culms (again a total of
15 culms). The former would be preferable for shoot production systems (more younger culms) and the latter for
pole or culm production (older culms are preferable for most purposes). Of interest, weight per harvested shoot
was not affected by thinning regime in the NT, or by the spatial arrangement of standing culms in Queensland
(widely spaced versus narrow spacing within a clump – Midmore 2009a).
Leaving all shoots to grow into culms causes congestion in the clumps, and constrains production of shoots in
later years. For this reason, some minimal annual thinning of culms or shoots is necessary if clumps are to
continue to produce shoots (and culms) on a sustained basis.
Species
Bamboo species harvested for shoots number less than 50, but even this number represents a great diversity in
terms of possible management practices specific to each species. Shoot number per unit area in bamboo with
large culm diameters (e.g., D. asper) are considerably fewer than in smaller-shoot-producing species Bambusa
oldhamii. With clumps close to 10 years of age, the latter produce on average over 20 shoots per clump in
optimally managed treatments in Queensland (Zhu et al. 2009). In contrast, the mature Dendrocalamus asper
(giant bamboo) of Bukidnon produces few shoots, on average c. 1 shoot per standing culm (Decipulo et al
2009), but they are large if harvested for consumption (reaching 4.5 kg). Age of the clump also affects shoot
number. Young clumps for example of D. latiflorus in the NT of Australia, aged between 3.5 and 4 years
VIII World Bamboo Congress Proceedings Vol 4-74