Abstract
Anthropogenic disturbances (cultivation, harvesting of poles and firewood and protection) play a pivotal role in the recovery and growth of Baikiaea-Guibourtia-Pterocarpus woodland species. The aim of this study is to determine the reliability of tree growth rings in age determination and average radial growth of re-growing woodland stands. The relationship between stem diameter, number of growth rings, and age of selected stands was also investigated. The research assisted in understanding the growth patterns of the key commercial timber species (Baikiaea plurijuga, Guibourtia coleosperma and Pterocarpus angolensis) of the seasonally dry Baikiaea-Guibourtia-Pterocarpus woodlands around Gwaai and Tsholotsho in north-western Zimbabwe. Tree rings were physically counted on basal stem cross-sections collected from 20 trees of different age, for each species in each disturbance regime. STATISTICA statistical package version 7.0 (StaSoft inc, 1984 - 2006) was used for data analysis. The Simple Regression Model was used to test for relationships. The relationship between age and growth rings, showed a strong correlation (p<0.0001). Diameter and number of growth rings had a poor correlation. This showed that growth rings and not diameter can be used to determine the age of the three key timber species. Mean annual ring width was significantly different between species within the same disturbance category (p<0.005) within a specific stand age. Mean radial growth was highest in abandoned crop fields, compared to pole and firewood collection sites. It was therefore concluded that forest managers need to adopt disturbance regimes that prompt optimal mean radial growth of at least key species in the woodlands. Key words: Disturbance, mean radial growth, tree rings, Baikiaea plurijuga, Guibourtia coleosperma; Pterocarpus angolensis.  
Highlights
Information on growth rates is key in determining the sustainability of harvesting systems and the formulation of sound forest management systems (Caetano et al., 2019; Khai et al, 2020) in natural forest and woodland systems
How can forest managers determine the age and growth rates of indigenous tree species when it is difficult to raise them in plantations? some tropical and sub-tropical tree species can produce growth rings which correlate with age (Fahn et al, 1981; Gourlay and Barnes, 1994; Grundy, 1995; Stahle et al, 1999; Geldenhuys, 2005; Ngoma et al, 2017)
The following research questions guided data collection and analysis: a) Can the individual growth rings be reliably differentiated on cut stems of key tree species in the woodlands? b) Is the number of growth rings the same in larger and smaller stems in a stand of known age? c) Can growth rings be more clearly differentiated in free-growing trees than in suppressed trees? d)Is there a relationship between the number of growth rings, stem diameter and stand age of a selected site, and can such a relationship be used for reliable stand age determination? and e) How does the mean radial growth of key tree species vary in different disturbance factors?
Summary
Information on growth rates is key in determining the sustainability of harvesting systems and the formulation of sound forest management systems (Caetano et al., 2019; Khai et al, 2020) in natural forest and woodland systems. Annual growth rings have been used in the past by forest managers in determining the age of Miombo woodlands in Zambia (Fanshawe, 1956; Syampungani et al, 2010) and in Zimbabwe (Grundy, 1995; Stahle et al, 1999). Syampungani et al (2010) showed that ring counts can be used in age determination, with a strong correlation between growth rings, known stand age, and stem diameter, for three Miombo woodland species. B. plurijuga was studied in Zambia by Miller (1952) about the determination of age and rotations and by Ngoma et al (2017) in terms of dendrochronological potential Both Miller (1952) and Ngoma et al (2017) highlighted that B. plurijuga shows clear annual growth rings. They did not analyze the relationship between the number of growth rings, age of the study site and stem diameter
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