Logging scars in Ghanaian high forest: towards improved models for sustainable production
Hawthorne, WD, Sheil, D, Agyeman, VK, Abu Juam, M & Marshall, CAM 2012, 'Logging scars in Ghanaian high forest: towards improved models for sustainable production', Forest Ecology and Management, vol. 271, pp. 27-36.
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We analyse data from 12 permanent sample plots (PSPs) in Ghana to determine recovery rates of skid trails and gaps in forest logged 10–30 years previously. We examine four key indicators of recovery – basal area, mortality rate, diameter increment and changes in the balance of tree guilds (Pioneer Index) – to compare the forest directly affected by logging (the apparent extraction network, AEN), with adjacent, less damaged forest. Data are presented on gaps created by felling individuals of different species and diameter, with a view to refining existing yield allocation procedures.
Our results indicate that forest recovery is slower than predicted by commonly used yield models. The basal area of AEN forest is below 23 m2 ha−1 in all 12 plots, even 30 years after logging, and is not obviously increasing. Initially elevated annual mortality rates return to normal rates of less than 2% after 15 years in the non-AEN forest, and after 22 years in the AEN forest. Diameter increments peak early for pioneers, and increase linearly for shade-bearers across the 10–30 year period, but are not translated into gains in basal area. Only in one plot does the Pioneer Index of the AEN approach that of the less disturbed surrounding forest, implying inertia against canopy closure, as pioneers replace pioneers. We conclude that Ghana’s commercial logging practices are not sustainable on the current 40-year felling cycle.
A different approach is required to achieve a sustainable harvest. Yield models will need to account for reduced site productivity. We suggest improved yield allocation through: (i) the development and use of electronic stock-maps to plan yield allocation, and as a basis for monitoring, (ii) accounting for species–specific differences, and (iii) collecting further data on the varied productivity of old extraction routes. Future studies should try to relate soil type to logging-impacts and recovery.