Harvesting and extraction impacts on Eucalyptus grandis × E. urophylla coppicing potential and rotation-end volume in Zululand, South Africa
From the early 2000s there has been a general shift in South Africa in harvesting and extraction systems from the use of semi- to fully-mechanised systems. Any increase in mechanisation, as is occurring in Zululand, will need to take into consideration damage to stumps and the subsequent ability to regenerate by coppice. In 2002, four types of harvesting and extraction systems, arranged in a randomised complete block design, were used to clearfell a stand of E. grandis × E. urophylla. A motor-manual harvesting system was used to carry out the manual harvesting system (Man). The fully mechanised system (Mech) consisted of a single-grip harvesting head used with a tracked excavator to carry out all felling and processing operations. Two additional systems (Man_Mech_3W and Man_Mech_Flexi) had increased levels of mechanisation over that of the Man treatment. Both these harvesting systems made use of a Bell debarker, with loading carried out by a Bell three-wheeled loader in the Man_Mech_3W, and by a Flexiloader in the Man_Mech_Flexi treatments. Data collected from these four treatments were used to determine the effects of mechanised harvesting systems on type and severity of stump damage, coppicing potential and coppice growth over the rotation. Irrespective of harvesting system, more damage occurred to the top than bottom half of the stump, with a significant decrease in coppice regrowth with increasing stump damage. Most damage and least coppice regrowth occurred in the extraction rows where the damage recorded could be attributed to vehicle movement, tear-outs and/or log stripping. There was no significant difference between the harvesting systems in terms of stump mortality, final stem stocking and rotation-end volume. Thus, individual components within each harvesting system can have a larger impact than the overall harvesting system used. Future research should focus on these components, and where associated damage occurs for a specific component, this should be lessened through management intervention, training or technological improvements.
Keywords: eucalypts, forest engineering, mechanised harvesting, shoots, sprouting