Effects of resin tapping on the visual, physical and strength properties of Pinus caribaea grown in Uganda

Abstract

Non-timber forest products, such as pine resin, provide significant economic benefits. In Uganda, resin is harvested by tapping pine stems for uses including adhesives, sealants, fire starters, and incense. However, this practice is relatively new and largely unregulated, raising concerns about potential impacts on tree health and timber quality, such as discoloration, fungal infections, and weakened wood, which may discourage farmers. This study aimed to support the sustainable and profitable development of resin-tapping enterprises in Uganda. Data were collected from mid-northern, southeast, and western Uganda, and Lake Victoria crescent agroecological zones. Random tree samples from tapped stands of two and five years were selected, and timber specimens were air-dried and prepared into small clear samples following ASTM standards. Physical and mechanical properties, including density, volumetric shrinkage, modulus of elasticity (MOE), shear strength, and compressive strength, were measured. The tapped timber was darker (reddish-brown) compared to light-yellow controls. There was no significant difference in the volumetric shrinkage of the tapped and non-tapped pine wood. Five-year tapped trees exhibited the highest strength (MOE: 8843 MPa, compressive: 13.045 MPa, shear: 12.70 MPa, max load: 1344.8 N), while two-year tapped trees were lower, and untapped trees had higher basic density. Among zones, mid-northern trees had the highest density, and southeast trees had the highest strength. Resin tapping did not negatively affect timber strength and may slightly enhance it, making tapped wood suitable for construction and furniture, though finishing is needed to address the darker color. Resin tapping is recommended in the southeast zone under proper silvicultural management. Further research should examine the effects of varying tapping durations across East Africa.