Tree selection in selective logging : ecological and silvicultural considerations for natural forest management in Ghana
This thesis was to examine selective logging practices in Ghana and to gather and apply relevant ecological and silvicultural knowledge to rules governing the selection of trees for felling (specifically minimum felling diameters and harvest intensities) and seed tree retention. The work involved reviews of historical data as well as field-based studies, including experimental and descriptive work. A review of forest regulation between 1900 and 1989 revealed that timber harvesting in permanent forest reserves has primarily been regulated through minimum felling limits. These regulations appear to have been insufficient to ensure regeneration of the valuable species, as suggested by examination of stem stocking and species composition data from six reserves that differ in levels of historical exploitation. The stock of timber trees in the logged forest is dominated by shade tolerant species indicating a need for silvicultural interventions. Census of seedlings and saplings within 50m of mother trees for 15 species revealed that more than 60% of their seedlings occur within 30m of parents indicating spatial limitation to seedling recruitment. The result also indicated that 14 of the species have reproductive size threshold lower than their respective minimum felling diameter (MFD) suggesting that decisions about seed tree retention could be uncoupled from MFDs. Logging studies to compare logging damage (ground area disturbed, stems damaged and canopy change) between two levels of harvest intensities (26.3m3 ha-1 and 52.6m3 ha-1) and two sizes (large and small) of tree selected for felling showed that doubling of harvest intensity increased the ground area disturbed by only 40%, but the higher felling intensity was associated with greater amount of canopy opening (mean loss of 21%) than the low intensity (mean loss of 9%).