Woody biomass increases across three contrasting land uses in Hurungwe, mid-Zambezi valley, Zimbabwe

Globally, Miombo woodlands store important quantities of carbon, with tree cover and carbon stocks strongly determined by human use. We assessed woodland cover and aboveground carbon (AGC) stocks of miombo along a utilisation gradient on three different land use types, that is, a national park, a buffer zone and a communal area. Woodland cover and carbon stock changes were assessed through mapping of AGC between 2007 and 2017 using Phased Array L-Band Synthetic Aperture Radar observations (ALOS-PALSAR 1 and 2). Woodland cover was higher in the national park and the buffer zone than in the communal area for both 2007 and 2017. In 2007, mean AGC stock was not significantly different (p = 0.005) across all three land use types. However, in 2017, mean AGC was significantly lower (p < 0.001) in the buffer zone and communal area than in the national park. In all three land use types, Miombo woodland cover and mean AGC gains outweighed losses over the 10-year period. AGC gains were significantly higher (p < 0.001) in the national park than in both the buffer zone and the communal area. Results of the study indicate that woodland cover and aboveground carbon increased in all three land use types despite the observed human disturbance over the study period. Both variables recorded a lower increase with elevated utilisation. The study concluded that sustainable resource utilisation is possible without loss of such ecosystem services as carbon sequestration and climate change mitigation

Climate change mitigation in Zimbabwe and links to sustainable development

In 2021, Zimbabwe updated its Greenhouse Gas (GHG) reduction target from a 33% reduction in per capita energy sector GHG emissions to a 40% reduction from all sectors, compared to 2030 baseline emission scenarios. This work aims to demonstrate how the actions identified in Zimbabwe's Nationally Determined Contribution (NDC) can achieve this updated target, and what development benefits could occur in Zimbabwe through the implementation of these actions. The magnitude of GHG emissions in Zimbabwe are modelled historically and to 2030 to quantify GHG emission reduction potentials, and contributions to selected sustainable development goal targets, from implementation of 28 mitigation measures. The estimated ∼37 million tonnes CO2-equivalent emissions emitted by Zimbabwe in 2017 are projected to increase by 109% to ∼77 million tonnes without implementation of any mitigation measures. The mitigation measures included in the updated NDC could reduce GHG emissions by 40% in 2030 compared to the baseline, while additional measures included in other plans and strategies in Zimbabwe could achieve a further 23% reduction. Implementing Zimbabwe's NDC could also lead to substantial development benefits locally, including to public health, biodiversity, and sustainable energy use. This assessment therefore provides a clear pathway to achieve Zimbabwe's updated climate change mitigation commitment, as the target is linked to the implementation of specific, concrete mitigation actions. It provides a practical example as to how methods to assess climate mitigation and development priorities can be integrated within climate change mitigation target-setting assessments. The more widespread adoption of prospective, quantitative assessment of development benefits from climate change mitigation actions could provide further motivation for more ambitious climate change action

Structural diversity and tree density drives variation in the biodiversity-ecosystem function relationship of woodlands and savannas

Positive biodiversity-ecosystem function relationships (BEFRs) have been widely documented, but it is unclear if BEFRs should be expected in disturbance-driven systems. Disturbance may limit competition and niche differentiation, which are frequently posited to underlie BEFRs. We provide the first exploration of the relationship between tree species diversity and biomass, one measure of ecosystem function, across southern African woodlands and savannas, an ecological system rife with disturbance from fire, herbivores and humans. We used >1000 vegetation plots distributed across 10 southern African countries, and structural equation modelling, to determine the relationship between tree species diversity and aboveground woody biomass, accounting for interacting effects of resource availability, disturbance by fire, tree stem density and vegetation type. We found positive effects of tree species diversity on aboveground biomass, operating via increased structural diversity. The observed BEFR was highly dependent on organismal density, with a minimum threshold of c. 180 mature stems ha-1. We found that water availability mainly affects biomass indirectly, via increasing species diversity. The study underlines the close association between tree diversity, ecosystem structure, environment and function in highly disturbed savannas and woodlands. We suggest that tree diversity is an under-appreciated determinant of wooded ecosystem structure and function

Structural diversity and tree density drives variation in the biodiversity–ecosystem function relationship of woodlands and savannas

Positive biodiversity–ecosystem function relationships (BEFRs) have been widely documented, but it is unclear if BEFRs should be expected in disturbance-driven systems. Disturbance may limit competition and niche differentiation, which are frequently posited to underlie BEFRs. We provide the first exploration of the relationship between tree species diversity and biomass, one measure of ecosystem function, across southern African woodlands and savannas, an ecological system rife with disturbance from fire, herbivores and humans. We used > 1000 vegetation plots distributed across 10 southern African countries and structural equation modelling to determine the relationship between tree species diversity and above-ground woody biomass, accounting for interacting effects of resource availability, disturbance by fire, tree stem density and vegetation type. We found positive effects of tree species diversity on above-ground biomass, operating via increased structural diversity. The observed BEFR was highly dependent on organismal density, with a minimum threshold of c. 180 mature stems ha−1. We found that water availability mainly affects biomass indirectly, via increasing species diversity. The study underlines the close association between tree diversity, ecosystem structure, environment and function in highly disturbed savannas and woodlands. We suggest that tree diversity is an under-appreciated determinant of wooded ecosystem structure and function