Harvesting intensity and disturbance to residual trees and ground under Myanmar selection system; comparison of four sites

The Myanmar selection system (MSS) has a long tradition for timber production in natural forests, mainly using elephants for skidding. We aimed to evaluate the levels of MSS disturbance to standing trees and the ground as compared with those reported for other tropical countries, and to identify possible ways to improve MSS operations. At each of four study sites, we established a 9-ha rectangular plot with nine 1-ha subplots. We measured all the living trees >10 cm diameter at breast height (DBH) in two of the subplots before felling, damage to residual trees immediately after felling operations and ground disturbance about 3 months after skidding operations in all nine subplots. Harvesting intensity varied from 0 to 18 trees ha⁻¹ (143.7 m³ ha⁻¹) with the mean of 5.2 trees ha⁻¹ (39.0 m³ ha⁻¹) among a total of 36 1-ha subplots. The harvesting intensity was linearly related to felling damage to residual trees (% trees) and bamboo clumps (% clumps), and to ground disturbance (% area) (roads, log landings, skid trails, and machine-disturbed areas). The damage and disturbance increasing with harvesting intensity were at the lowest level of, or not significantly different from, those reported in other studies. The lowest level of ground disturbance is because of the use of elephants for skidding, resulting in no visible ground disturbance only a few months after the operation. However, some felled trees were too large (>100 cm DBH) for elephant skidding, and so a bulldozer was used instead. The aid of the machine for skidding resulted in a greater proportion of disturbed area (2.4% of the area at Site 4). To minimize disturbance to residual trees and the ground, we suggest to limit the maximum harvesting intensity and avoid harvesting trees too big for elephants to drag. Retaining such large trees may also be beneficial to provide seed sources and for biodiversity conservation.