Tree Growth Rates and Their Determinants Inform Sustainable Harvesting of Indigenous Woodlands in Zimbabwe

ABSTRACT Tree growth rates determine ecosystem structure, community interactions, and sustainable harvesting rates. Understanding their determinants can provide insights into likely responses to global change but in southern African woodlands, such studies are sparse. This limits assessments of whether timber harvesting is sustainable and the quantification of carbon sequestration rates. We analyzed tree growth rates of 2466 individual stems belonging to 33 species tracked over 27 years on 11 permanent sample plots in Baikiaea plurijuga (Zambezi teak) woodlands of Zimbabwe using hierarchical mixed effects regression models. The median growth rate of an average species was 0.8 mm year −1 (range of species means = 0.2–2.6). Across key timber species, the mean time to reach a harvestable size of 35 cm diameter from 5 cm diameter was 150 years (range of species means = 114–189). Growth rates were faster during periods with high water availability ( p = 0.006) and at higher levels of atmospheric CO 2 ( p = 0.044). Stand level basal area, likely an indicator of tree‐tree competition, had a surprisingly strong effect on tree growth rates ( p = 0.006): doubling basal area (from 11 m 2 ha −1 to 22 m 2 ha −1 ) increased the mean time to harvestable size from 150 years to 292 years. These findings highlight the potential to increase productivity by managing competition through thinning and selective harvesting, but also imply strong responses of tree growth to global change drivers. We recommend that harvesting cycles should be informed by species‐specific growth rates, competition, and resource availability to achieve sustainable harvesting.