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The Assessment of Logging Damage: A Case Study in the Forest Concession Area of Colexim at Kompong Thom Province, Cambodia
Thesis Abstract:
A case study on logging damage was made in the Colexim forest concession. The study area lies in Kompong Province in the central part of Cambodia. It consists of flat terrain covered by tropical rainforest dominated by dipterocarp species. Logging followed the guidelines of Cambodian selective cutting system and took place in 1997.
The field investigations were made in 1998. The disturbance of the soil surface and damage of the remaining stand with diameters above 10 cm at breast height were investigated in six sample plots of 100 x 100 m, divided in two per high, medium and low logging intensities which were defined by the percentage of the basal area removed. The damage to the natural regeneration (saplings between diameters of 5 and 10 cm as well as between diameters of 1.5 and 5 cm, and seedlings up to a height of 1.5 m) was studied on sub-plots of 10 x 10 m, 5 x 5 m, and 2 x 2 m.
The disturbance of soil surface originated from felling gaps, skidding lines, temporary roads, and log landings. The damage to the remaining stand was divided into types of damage (accidental felling of neighboring trees, crown damage, bark damage, combination of crown and bark damage, root damage), degree of damage (light, medium, heavy), and cause of damage (felling, skidding, unknown, others).
The disturbance of soil surface reached a maximum value of 31 percent of the total surface (20% felling gaps, 11% skidding lines) when 35 percent of the basal area removed. The minimum value of 10 percent (6% felling gaps, 4% skidding lines) was observed when 7 percent of the basal area was harvested. Generally, the ratio of felling gaps to skidding trails was about 1.5:1. These were rather reasonable results compared with the research into other logging operations.
The damage to the remaining stand increased from 10 to 19 percent of the total basal area when the basal area harvested increased from 13 to 35 percent of the total basal area. These differences, however, only indicate a tendency because their statistical significance could not be proven due to the small number of sample plots per logging intensity. The damage to the reaming stand (above 10 cm dbh) affected 12 and 28 percent of the potential future crop trees. The largest number of damaged trees could be observed in the lowest diameter class of 10-20 cm which corresponds to the diameter distribution of the stand. There were, however, enough undamaged future crop trees in the higher diameter classes to allow the harvesting of target diameter trees in future cutting cycles.
The reasonable condition of the stand was further underlined by the large number of undamaged saplings and seedlings. It was so high that enrichment planting was not necessary. It was, however, advantageous to plant large felling gaps and skidding trails, or landings that will not be used in future logging operations.
The most frequent type of damage was accidental felling of neighboring trees (between 44% and 68% of all tree damages) mainly affecting the smallest diameter class (10-20 cm). The next frequent type was crown damage (between 14% and 29%) followed by bark damage or by combinations of the two with a tendency to affect higher diameter classes.
The most frequent cause of damage was felling followed by causes which could not be clearly defined and then by skidding. This indicates that even better results might be reached if the felling operation could be improved. Other improvements lie in a strict application of the principles of the Cambodian selective cutting system.
In general, the study demonstrated that the disturbance of the soil surface and the damage to the remaining stand as well as to natural regeneration reached favorable levels. This was the result of a limited number of trees harvested, the use of smallscale equipment for skidding, and the restriction of skidding to as few trails as possible. But there is still room for improvement, in particular in the felling operation through the use of directional (controlled) felling, and in the application of a cohesive silvicultural system for harvesting and tending.