Trees are vital to rural agricultural livelihoods in drylands. They provide several ecosystem services including food, fuel, and energy, as well as income generating activities such as bee keeping. African drylands, which cover 43% of the continent are prone to land degradation and desertification.
In turn, land degradation and the associated loss of vegetation cause biodiversity loss and contribute to climate change through reduction in carbon sequestration (Vågen and Winowiecki, 2013). However, increasing tree diversity and cover and herbaceous ground cover can significantly help to combat these complex and interrelated phenomena thanks to the role of trees in stabilizing soils, reducing water and wind erosion, and maintaining nutrient cycling in the soils. Sustainable use of goods and services from tree-based livelihood ecosystems and the development of agroforestry can, therefore, contribute to poverty reduction, making the rural dryland communities less vulnerable to the impacts of land degradation.
Restoration of drylands, including both increasing tree diversity and cover as well as overall ecosystem function, has become a major priority for international, national, and local initiatives (IUCN and WRI, 2014). The United Nations Convention to Combat Desertification (UNCCD) and the UN Environment Programme (UNEP) recognize the threat of land degradation and launched the ‘2030 Agenda for Sustainable Development’. Specifically, Sustainable Development Goal (SDG) 15 aims to "protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss," while the SDG target 15.3 aims to achieve Land Degradation Neutrality.
The initiative on Land Degradation Neutrality (LDN) was launched in 2015 with national level targets for indicators on (i) trends in land use/cover, (ii) land productivity and (iii) soil organic carbon stocks. The World Agroforestry Centre (ICRAF)has produced a report on methods to assess these indicators, as well as a fourth indicator, soil erosion. The Land Degradation Surveillance Framework (LDSF), developed by ICRAF is widely used to systematically assess land and soil health across diverse landscapes. Data from field surveys using the this framework indicate that maintaining and restoring both herbaceous layers and woody cover in semi-arid lands is important for curbing land degradation processes such as soil erosion, and for increasing overall land productivity. Soil organic carbon is also a key indicator of soil health, and land management options to increase soil organic carbon can also help increase overall productivity and improve the resilience of ecosystems. Our research across sub-Saharan Africa shows that reducing soil erosion and increasing tree cover can increase soil organic carbon, pointing to the importance of examining and understanding such complex system interactions in landscapes instead of focusing on single options or mono-disciplinary solutions to address the drivers that cause the processes of land degradation and desertification to happen.
Specifically, in semi-arid parts of northern Kenya, higher soil organic carbon was found in areas with higher tree cover coupled with moderate grazing and high herbaceous cover (Vagen and Winowiecki, 2014). In semi-arid lands of central Kenya, high soil erosion prevalence was related to decreasing soil organic carbon across a range of vegetation classes. There were also strong effects of woody and herbaceous cover, with higher soil organic carbon in plots with 40% or more woody cover and 15% or more herbaceous cover.
Trees are crucial to life, health, nutrition and general well-being in drylands. Under the framework of the CGIAR Research Program on Dryland Systems, ICRAF has developed the Options-by-Context Approach, which acknowledges that fine-scale variations in social, ecological, and economic realities across the landscape are critical and important for developing context-specific solutions that can be locally adopted and scaled out and up to more communities. For example, farmers consider many different factors when making farm management decisions, including restoration options such as which tree to plant, where, and for what purpose. For this reason, we combine farmers’ knowledge on the benefits of specific trees for specific places with systematic land and soil health surveys to identify the best restoration options across a range of contexts. This allows us to determine what ingredients and combinations of research and policy interventions work where and for whom. If we are to achieve the restoration goals laid out in the Bonn Challenge and the newly launched Africa Restoration Initiative, we need to take a systems approach to examining and developing practical restoration solutions alongside farmers, and adopt and scale up those that provide multiple environmental and socio-economic benefits to improve rural livelihoods and ensure healthier ecosystems for generations to come.
About the authors
Leigh Winowiecki is a Soil Systems Scientist at the World Agroforestry Centre (ICRAF) based in Nairobi, Kenya. She currently leads the IFAD-funded project, “Restoration of degraded land for food security and poverty reduction in East Africa and the Sahel: taking successes in land restoration to scale,” which is an example of a Research in Development project to out-scale restoration activities.
Tor-Gunnar Vågen is Senior Scientist and head of the GeoScience lab at the World Agroforestry Centre (ICRAF). He has a background from soil science, hydrology, landscape ecology, statistical modeling and remote sensing. Dr. Vågen is working with colleagues towards the establishment of a global network of sites for comparative assessments of ecosystem health and linkages between biophysical and socio-economic variables in order to understand drivers of deforestation, land use change and land degradation across the global tropics.
- IUCN and WRI (2014). A guide to the Restoration Opportunities Assessment Methodology (ROAM): Assessing forest landscape restoration opportunities at the national or sub-national level. Working Paper (Road-test edition). Gland, Switzerland: IUCN. 125pp.
- Vågen, Tor-Gunnar; Winowiecki, Leigh A. 2013. Mapping of soil organic carbon stocks for spatially explicit assessments of climate change mitigation potential. Environmental Research Letters. 8 (1): 1-9.
- Vågen, Tor-Gunnar; Winowiecki, Leigh. 2014. Northern Rangelands Trust: Baseline assessment of rangeland health - Kalama and Namunyak conservancies. World Agroforestry Centre (ICRAF) and International Center for Tropical Agriculture (CIAT).