CHAINSAW MILLING IN GHANA: CONTExT, DRIVERS ... - Fornis.net

Chapter 3. Timber production and tradeTwo of these studies estimated the annual volume of trees harvested by chainsawoperators and elaborated the methodologies. Birikorang et al. (2001) used marketsurvey data to estimate the annual harvest at 1.7 million m 3 ; Hansen et al. (2008)argue that this is a conservative estimate for the period 1999–2005. Marfo, Adamand Obiri (2009) used the estimated number of chainsaw operators and theirannual production figures to calculate the annual harvest at 2.4 million m 3 . Basedon a critical assessment of the available information from those studies, and newinformation from a recent market survey (TIDD/FORIG 2009), a revised estimate isprovided in the following sections.These estimates of the annual harvest by chainsaw operators incorporate, anddepend on, two main parameters which are both problematic in their measurement:• the estimated average conversion efficiency of logs into lumber by chainsawoperators (section 3.5.2); and• the total volume of chainsawn lumber supplied to the domestic market, pluslumber exported overland (section 3.5.3).3.5.2 Conversion efficiencyConversion efficiency data are highly variable, as they depend on a large number offactors, including the skill of the operator, the product to be cut, defects in the tree,size and shape of the log, species-specific differences in processing characteristics,and the basis used to calculate volumes and conversion factors. Processing Efficiency(PE) refers to the rate of recovery based on the volume of the log processed. Conversionefficiency (CE) is based on the volume of the whole tree. In order to reconcilethe discrepancies in efficiency data between studies, recovery efficiency should bemeasured by the total volume of lumber recovered from the total usable volume ofthe tree; i.e., by conversion efficiency.Reported conversion efficiencies for CSM cited in the literature range from 27–40%(Table 11), with an average of 30.3%. 2Table 11. Reported conversion efficiencies (means and range) of chainsaw operationssource processing efficiency (%) conversion efficiency (%)Birikorang et al. 2001 *39 27Frimpong-Mensah 2004 40 (22–51) ** 28 (15–36)Gyimah and Adu-Gyamfi 2009 51 ** 36Owusu et al. 2009 43 (32–57) ** 30 (22–40)average ± standard deviation 43.1 ± 5.6 30.3 ± 4.0* reported estimate of 27% multiplied by 1.43 to account for 70% log recovery rate** multiplied by the 70% rate of log recovery (Owusu et al. 2009) where butt and top end residues were notincluded in the conversion efficiency estimate23