Urban harvest pressures: Bark stripping of African Mahogany (Khaya senegalensis) trees for medicinal use in the Northern Region of Ghana

Abstract

Background: Khaya senegalensis (Desr.) A.Juss. (African mahogany) is planted in urban landscapes as an amenity tree but also exploited for medicinal bark. However, little is known about bark stripping pressure and its link to urban tree health. This study was aimed at assessing the extent and intensity of bark-stripping among African mahogany trees in urban spaces and examining associations between bark-stripping, stem burl formation and stem decay.

Methods: Field survey was conducted in three districts (Tamale, Sagnarigu and Tolon) in the northern region of Ghana between 2017 and 2018. Multi-stage sampling together with tree inventory techniques were used to assess tree height, diameter at breast height (DBH), presence of bark stripping, stem burls, stem decay, and stripping intensity of bark-stripped trees. Data were analysed using descriptive statistics as well as logistic regression and chi-square tests to assess relationships among variables.

Results: A total of 509 African mahogany trees were assessed across the three districts. Bark-stripping was intensive and widespread (80% of trees). Prevalence was highest in Tolon district compared to the more urbanized Tamale Metropolis. Bark-stripping was a significant predictor of stem burl formation (p < 0.001), which in turn significantly predicted stem decay (p = 0.039). Bark-stripped trees were 26 times more likely to develop stem burls, and trees with stem burls were four times more likely to show stem decay.

Conclusions: Bark-stripping intensity is high among urban African mahogany trees in the Northern Region of Ghana and is associated with burl formation and increased risk of stem decay.

Keywords: Ethnobotany, stem decay, stem burls, tree health, amenity trees