How have carbon stocks in central and southern Africa’s miombo woodlands changed over the last 50 years? A systematic map of the evidence
Miombo woodlands cover ≈ 2.7 million km2 of central and southern Africa between dry (650 mm mean annual rainfall) and moist miombo (1400 mm) and are currently threatened by land use and land cover changes that have intensified over the last 50 years. Despite the miombo’s global significance for carbon (C) storage and sequestration, there has been no regional synthesis that maps carbon stocks and changes in the woodlands. This information is crucial to inform further research for the development of appropriate policies and management strategies to maintain and increase C stocks and sequestration capacity, for conservation and sustainable management. We assembled a systematic map to determine what evidence exists for (1) changes in carbon stocks in miombo woodlands over the period 1960–2015; (2) differences in carbon density in miombo with different conservation status; (3) trends in carbon stock recovery following human disturbance; and (4) fire management impacts on carbon stocks and dynamics.
We screened 11,565 records from bibliographic databases and grey literature sources following an a priori research protocol. For inclusion, each study had to demonstrate the presence of miombo-typical species (Brachystegia, Julbernardia and Isoberlinia) and data on above- or below-ground carbon stocks or plant biomass.
A total of 54 articles met the inclusion criteria: 48 quantitative and eight qualitative (two of which included quantitative and qualitative) studies. The majority of studies included in the final analyses are largely quantitative in nature and trace temporal changes in biomass and carbon in the miombo woodlands. Studies reported a wide range (1.3–95.7 Mg ha−1) of above-ground carbon in old-growth miombo woodland. Variation between years and rainfall zones and across conservation area types was large.
An insufficient number of robust studies that met our inclusion criteria from across the miombo region did not allow us to accurately pool carbon stocks and trends in miombo old growth. Thus, we could not address the four questions originally posed in our protocol. We suggest that future studies in miombo woodlands take longer term observational approaches with more systematic, permanent sampling designs, and we identify questions that would further warrant systematic reviews, related to differences in C level recovery after disturbance in fallow and post-clearing re-growth, and the role of controlled fire management.
Biomass, Brachystegia, Carbon stocks, Conservation area status, Fire management, Isoberlinia, Julbernardia, Old-growth, Re-growth, Soil organic matter
Increasingly, forests are on the international climate change agenda as land use and cover changes drive forest and carbon loss. The ability of forests to store carbon has created programs such as Reducing Emissions from Deforestation and Degradation plus (REDD+), in order to provide incentives for particular land uses and forest management practices. A critical element to REDD+ is the ability to know the carbon-storage potential of an ecosystem, and the factors likely to affect the rate of carbon accumulation or the maximum amount stored. Most REDD+ initiatives have focused on humid tropical forests because of their large stocks per unit area. Less attention has been paid to the carbon-storage potential of tropical dry forests, woodlands and savannas. Although these ecosystems support a lower biomass per unit area, they are more widespread than humid forests. This proposed systematic review examines miombo woodlands, which are the most extensive vegetation formation in Africa and support over 100 million people. We ask: To what extent have changes in land use and land cover influenced above- and below-ground carbon stocks of miombo woodlands since the 1950s?
We will search systematically for studies that document the influence of land use and cover change on above and below ground carbon in miombo woodlands since the 1950s. We will consult bibliographic databases and an extensive grey literature network, including government reports and forestry offices. Relevant studies will examine the impacts of human activities, fire and other land use or cover changes that affect wood biomass or soil carbon in the miombo region. All included studies will be assessed for the soundness and scientific validity of their study design. A quantitative synthesis will tabulate estimates of various parameters necessary to assess carbon stocks and changes across climate and geological factors; and a qualitative analysis will describe the governing land and forest policies. Understanding the impact that land uses and the associated changes have on carbon storage in the miombo woodlands will contribute to more informed forest management policies and better guided strategies for the United Nations Framework Convention on Climate Change.