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G. Gray Tappan

Publications and source records attributed to G. Gray Tappan.

At least 19 recordsLinked to original sources

Land use change and climate-smart agriculture in the Sahel

In the 1970s and 1980s, the Sahel experienced recurrent drought and famine. Farmers and their development partners reacted to this crisis by developing climate-smart agricultural practices and changes in land use, including water-harvesting techniques to restore degraded land to productivity. In several densely populated parts of the Sahel, farmers began to protect and manage woody species that regenerated naturally on their farmland. Farmer-managed natural regeneration (FMNR) is a foundational practice that produces multiple benefits, such as maintaining or improving soil fertility, which raises crop yields, and increasing the production of tree-based fodder, fruit, and firewood. In Niger’s Maradi and Zinder Regions alone, farmers have applied FMNR practices on 4.2 million hectares. The findings presented in this chapter suggest that the future of agriculture in the Sahel will be largely determined by whether low-income smallholder farmers will manage to improve soil fertility, which will depend on maintaining substantial densities of on-farm trees thus increasing tree cover.

Sahel Region↗

Assessing cropland area in west Africa for agricultural yield analysis

Accurate estimates of cultivated area and crop yield are critical to our understanding of agricultural production and food security, particularly for semi-arid regions like the Sahel of West Africa, where crop production is mainly rain-fed and food security is closely correlated with the inter-annual variations in rainfall. Several global and regional land cover products, based on satellite remotely-sensed data, provide estimates of the agricultural land use intensity, but the initial comparisons indicate considerable differences among them, relating to differences in the satellite data quality, classification approaches, and spatial and temporal resolutions. Here, we quantify the accuracy of available cropland products across Sahelian West Africa using an independent, high-resolution, visually interpreted sample dataset that classifies all points across West Africa using a 2-km sample grid (~500,000 points for the study area). We estimate the “quantity” and “allocation” disagreements for the cropland class of eight land cover products in five Western Sahel countries (Burkina Faso, Mali, Mauritania, Niger, and Senegal). The results confirm that coarse spatial resolution (300 m, 500 m, and 1000 m) land cover products have higher disagreements in mapping the fragmented agricultural landscape of the Western Sahel. Earlier products (e.g., GLC2000) are less accurate than recent products (e.g., ESA CCI 2013, MODIS 2013 and GlobCover 2009). We also show that two of the finer spatial resolution maps (GFSAD30, and GlobeLand30) using advanced classification approaches (random forest, decision trees, and pixel-object combined) are currently the best available products for cropland identification. However, none of the eight land cover databases examined is consistent in reaching the targeted 75% accuracy threshold in the five Sahelian countries. The majority of currently available land cover products overestimate cultivated areas by an average of 170% relative to the cropland area in the reference data.

Remote Sensing↗

Farmer-managed restoration of agroforestry parklands in Niger

Land rehabilitation enables sustainable intensification of agriculture and more resilient food production systems. Despite severe development challenges, Niger is the site of successful, farmer-managed efforts to counteract the global trend in land degradation that was supported by policy change. The vast majority of Niger’s land is located in the Sahara. Following a series of severe droughts during the 1970s, it seemed as if the harmattan would blow drought-stricken Niger from the map. In 1993, an enabling policy change in government regulations transferred the ownership of trees from the state to farmers. Even before the policy was enacted, farmers had begun restoring agroforestry parklands on the heavily populated, agricultural plains of south-central Niger. By 2005, the sparse tree cover of the 1970s was replaced by young and fastgrowing parklands, with a high density of trees, often in the inner fields around a village. Village sizes continued to swell, with fallow continuing to disappear. Yet, comparing 2005 to 2013, high resolution imagery in 2013 showed almost no change in most sample plots, increasing tree density on nearly a quarter of them, and decreasing density in less than 2%. In 2017, an estimated 7 million ha are affected by the process of farmer-managed natural regeneration (FMNR) – a scale and longevity that attests to the economic viability of the approach.

Book chapter↗

Woody vegetation die off and regeneration in response to rainfall variability in the west African Sahel

The greening in the Senegalese Sahel has been linked to an increase in net primary productivity, with significant long-term trends being closely related to the woody strata. This study investigates woody plant growth and mortality within greening areas in the pastoral areas of Senegal, and how these dynamics are linked to species diversity, climate, soil and human management. We analyse woody cover dynamics by means of multi-temporal and multi-scale Earth Observation, satellite based rainfall and in situ data sets covering the period 1994 to 2015. We find that favourable conditions (forest reserves, low human population density, sufficient rainfall) led to a rapid growth of Combretaceae and Balanites aegyptiaca between 2000 and 2013 with an average increase of 4% woody cover. However, the increasing dominance and low drought resistance of drought prone species bears the risk of substantial woody cover losses following drought years. This was observed in 2014–2015, with a die off of Guiera senegalensis in most places of the study area. We show that woody cover and woody cover trends are closely related to mean annual rainfall, but no clear relationship with rainfall trends was found over the entire study period. The observed spatial and temporal variation contrasts with the simplified labels of “greening” or “degradation”. While in principal a low woody plant diversity negatively impacts regional resilience, the Sahelian system is showing signs of resilience at decadal time scales through widespread increases in woody cover and high regeneration rates after periodic droughts. We have reaffirmed that the woody cover in Sahel responds to its inherent climatic variability and does not follow a linear trend.

Senegalese Sahel↗

Landscapes of West Africa: A window on a changing world

Our global ecosystem is and has always been complex, dynamic, and in constant flux. Science tells us how natural forces of enormous power have shaped and reshaped Earth’s surface, atmosphere, climate, and biota again and again since the planet’s beginnings about 4.5 billion years ago. For most of the planet’s history those environmental changes were the result of the interaction of natural processes such as geology and climate and were described on the geological time scale in epochs spanning millions of years. When humankind appeared on Earth around 200,000 years ago the influence of human activity on the environment must have been small and localized. The influence of scattered small groups of people on the global ecosystem would have been overwhelmed by the forces of natural systems (Steffen and others, 207). Human population would not grow to 50 million (about 0.7 percent of the Earth’s current population) for another 197,000 years. Population growth accelerated over the centuries that followed until the planet was adding more than that 50 million people every year. Our planet is now home to roughly 7.3 billion people and we are adding 1 million more people roughly every 4.8 days (US Census Bureau, 2011). Before 1950, no one on Earth had lived through a doubling of the human population, but now some people have experienced a tripling in their lifetime (Cohen, 2003).

Book↗

Vegetation impoverishment despite greening: a case study from central Senegal

Recent remote sensing studies have documented a greening trend in the semi-arid Sahel and Sudan zones of West Africa since the early 1980s, which challenges the mainstream paradigm of irreversible land degradation in this region. What the greening trend means on the ground, however, has not yet been explored. This research focuses on a region in central Senegal to examine changes in woody vegetation abundance and composition in selected sites by means of a botanical inventory of woody vegetation species, repeat photography, and perceptions of local land users. Despite the greening, an impoverishment of the woody vegetation cover was observed in the studied sites, indicated by an overall reduction in woody species richness, a loss of large trees, an increasing dominance of shrubs, and a shift towards more arid-tolerant, Sahelian species since 1983. Thus, interpretation of the satellite-derived greening trend as an improvement or recovery is not always justified. The case of central Senegal represents only one of several possible pathways of greening throughout the region, all of which result in similar satellite-derived greening signals.

Journal of Arid Environments↗

Land cover change, biogeochemical modelling of carbon stocks, and climate change in West Africa

The carbon in ecosystems exists in dynamic soil and vegetation pools which vary in amounts and cycle with the global atmosphere at varying rates. These stocks and fluxes play important roles in global carbon regulation and in the maintenance of goods and services. Changes in land cover or ecosystems result in increased or decreased fluxes to the atmosphere and play a major role in climate regulation. Carbon in soil is closely coupled to soil nitrogen and the continued mining of soil for crops or fuel without replenishment of nutrients results in decreased productivity and impacts food security. The assessment of these processes across large areas, although difficult, is aided by the integration of simulation modelling (biogeochemical and ecosystem) and remote sensing. We acquired satellite imagery for four periods from the 1960s to 2000s, trained environmental scientists from 14 countries on image analysis and interpretation, and now report systematic analyses of land cover changes in select countries of West Africa and quantify potential impacts of climate change and management at specific sites. Statistical changes and maps of land cover are documented for most countries. Senegal, for example, illustrates a 57 percent loss in dense forests between 1975 and 2000 with an even greater loss rate in the preceding 10 years. Bare soil increased 16.6 percent, often related to unproductive “badland” formation. Settlements increased 45.6 percent, and reforestation replaced bare sandy areas for sand dune stabilization. In some countries (Senegal and Ghana), the impact of these conversions and changes in land management and future projections has been incorporated into biogeochemical models to quantify carbon changes and project future carbon and crop scenarios. We present current assessments of carbon fluxes and the availability of data for these West African countries.

Conference Paper↗

Agroenvironmental transformation in the Sahel: Another kind of "green revolution"

A farmer-managed, agroenvironmental transformation has occurred over the past three decades in the West African Sahel, enabling both land rehabilitation and agricultural intensification to support a dense and growing population. This paper traces the technical and institutional innovations, their impacts, and lessons learned from two successful examples. The first is the story of the improvement and replication of indigenous soil and water conservation practices across the Central Plateau of Burkina Faso. Rehabilitation of at least 200,000 hectares of degraded land enabled farmers to grow cereals on land that had been barren and intensify production through developing agroforestry systems. Additionally, rehabilitation appears to have recharged local wells. The second example is a farmer-managed process of natural regeneration, using improved, local agroforestry practices over an estimated 5 million hectares in southern Niger. This large-scale effort reduced wind erosion and increased the production and marketing of crops, fodder, firewood, fruit, and other products. In both cases, income opportunities were created, reducing incentives for migration. Women benefited from the improved supply of water, fuelwood, and other tree products. Human, social, and political capital was strengthened in a process of farmer-driven change. Fluid coalitions of actors expanded the scale of the transformation. These stories have important lessons for those who seek to create effective agricultural development partnerships and meet the challenges of climate change and food security.

Central Plateau, West African Sahel↗

Re-greening the Sahel: Farmer-led innovation in Burkina Faso and Niger

The Sahel—the belt of land that stretches across Africa on the southern edge of the Sahara—has always been a tough place to farm. Rainfall is low and droughts are frequent. The crust of hard soil is, at times, almost impermeable, and harsh winds threaten to sweep away everything in their path. Over the past three decades, however, hundreds of thousands of farmers in Burkina Faso and Niger have transformed large swaths of the region’s arid landscape into productive agricultural land, improving food security for about 3 million people. Once-denuded landscapes are now home to abundant trees, crops, and livestock. Although rainfall has improved slightly from the mid-1990s relative to earlier decades, indications are that farmer management is a stronger determinant of land and agroforestry regeneration. Sahelian farmers achieved their success by ingeniously modifying traditional agroforestry, water, and soil-management practices. To improve water availability and soil fertility in Burkina Faso’s Central Plateau, farmers have sown crops in planting pits and built stone contour bunds, which are stones piled up in long narrow rows that follow the contours of the land in order to capture rainwater runoff and soil. These practices have helped rehabilitate between 200,000 and 300,000 hectares of land and produce an additional 80,000 tons of food per year. In southern Niger, farmers have developed innovative ways of regenerating and multiplying valuable trees whose roots already lay underneath their land, thus improving about 5 million hectares of land and producing more than 500,000 additional tons of food per year. While the specific calculations of farm-level benefits are subject to various methodological and data limitations, the order of magnitude of these benefits is high, as evidenced by the wide-scale adoption of the improved practices by large numbers of farmers. Today, the agricultural landscapes of southern Niger have considerably more tree cover than they did 30 years ago. These findings suggest a human and environmental success story at a scale not seen anywhere else in Africa. The re-greening of the Sahel began when local farmers’ practices were rediscovered and enhanced in simple, low-cost ways by innovative farmers and nongovernmental organizations. An evolving coalition of local, national, and international actors then enabled large-scale diffusion and continued use of these improved practices where they benefited farmers.

Sahel↗

Tracking environmental dynamics and agricultural intensification in southern Mali

The Office de la Haute Vallée du Fleuve Niger (OHVN) zone in southern Mali is a small but important agricultural production region. Against a background of environmental degradation including decades of declining rainfall, soil erosion, and human pressure on forest resources, numerous farming communities stand out through the use of improved soil and water management practices that have improved agricultural and environmental conditions. Field surveys conducted in 1998–2001 indicated that environmental and agricultural conditions have improved in the past decade. In an effort to better quantify environmental trends, we conducted a study using medium- and high-resolution remotely sensed images from 1965 to 2001 in order to analyze land use and land cover trends in 21 village territories. The trends show clear indications of agricultural intensification and diversification among villages that have received assistance from the OHVN agricultural development agency. Some communities have improved environmental conditions by protecting their forest resources through community management actions. Four decades of remotely sensed images played a practical role in tracking and quantifying environmental and agricultural conditions over time.

Agricultural Systems↗

Ecoregions and land cover trends in Senegal

This study examines long-term changes in Senegal's natural resources. We monitor and quantify land use and land cover changes occurring across Senegal using nearly 40 years of satellite imagery, aerial surveys, and fieldwork. We stratify Senegal into ecological regions and present land use and land cover trends for each region, followed by a national summary. Results aggregated to the national level show moderate change, with a modest decrease in savannas from 74 to 70 percent from 1965 to 2000, and an expansion of cropland from 17 to 21 percent. However, at the ecoregion scale, we observed rapid change in some and relative stability in others. One particular concern is the decline in Senegal's biodiverse forests. However, in the year 2000, Senegal's savannas, woodlands, and forests still cover more than two-thirds of the country, and the rate of agricultural expansion has slowed.

Journal of Arid Environments↗

Understanding the drivers of agricultural land use change in south-central Senegal

Described is (1) the land use and land cover changes that have taken place in the Department of Velingara, an area of tropical dry woodland in south-central Senegal, (2) the biophysical and socio-economic drivers of those changes with an emphasis on transition to agricultural use, and (3) an assessment of the likelihood of intensification of agriculture in the Department. Results indicate that land devoted to agriculture, either in active cultivation or short-term fallow, is increasing. There is little evidence of agricultural intensification in most of Velingara, with extensification coming largely at the cost of reduction in both upland woodlands and riparian forest.

Journal of Arid Environments↗

Ecological impact of historical and future land-use patterns in Senegal

The CENTURY model was used to simulate changes in total system carbon resulting from land-use history (1850–2000), and impacts of climatic changes and improved land-use management practices in Senegal. Results show that 0.477 Gtons of carbon have been lost from 1850 to 2000. Improved management practices have the potential of increasing carbon levels by 0.116 Gtons from 2000 to 2100. Potential to store carbon exists for improved forest management and agriculture practices in southern Senegal. Potential climatic changes decrease plant production (30 percent), total system carbon (14 percent), and the potential to store carbon from improved management practices (31 percent).

Journal of Arid Environments↗

Sequestration of carbon in soil organic matter in Senegal: an overview

Sequestration of Carbon in Soil Organic Matter ( SOCSOM ) in Senegal is a multi-disciplinary development project planned and refined through two international workshops. The project was implemented by integrating a core of international experts in remote sensing, biogeochemical modeling, community socio-economic assessments, and carbon measurements in a fully collaborative manner with Senegal organizations, national scientists, and local knowledge and expertise. The study addresses the potential role developing countries in semi-arid areas can play in climate mitigation activities. Multiple benefits to smallholders could accrue as a result of management practices to re-establish soil carbon content lost because of land use changes or management practices that are not sustainable. The specific importance for the Sahel is because of the high vulnerability to climate change in already impoverished rural societies. The project focuses on four objectives in specific locations across the agroecological zones of Senegal. These objectives are: use of soil sampling and biogeochemical modeling to quantify the biophysical potential for carbon sequestration and to determine the sensitivity of the carbon stocks to various management and climate scenarios, to evaluate the socio-economic and cultural requirements necessary for successful project implementation directed toward an aggregation of smallholders to sequester around 100,000 t carbon (C), to support capacity building to develop a Carbon Specialist Team, and to initiate extrapolation from site-specific project areas to the Sahel region and the national level.

Journal of Arid Environments↗

Use of Argon, Corona, and Landsat imagery to assess 30 years of land resource changes in west-central Senegal

Over the past 35 years, an agricultural area of west-central Senegal has experienced rapid population growth, fast expansion of agricultural lands, a decline in rainfall, and degradation of vegetative and soil resources. Although such changes have not escaped the attention of Senegal's people, its government, and the scientific community the ability to monitor and quantify land resource trends of recent decades has been difficult. Recently available high-resolution satellite photographs from the American Argon and Corona Programs provide coverage of Senegal back to 1963. The photographs make it possible to study and map land resources at the beginning of the Space Age. In this study, we characterize the changes that have occurred in the region from the early 1960s to the mid-1 990s. Early Argon and Corona photographs are used to reconstruct the historical land use and land cover; comparisons are made with assessments from recent Landsat images. Field studies and aerial surveys provide additional insight. The forces of change, driven primarily by population growth and unsustainable agricultural practices, are examined

Photogrammetric Engineering and Remote Sensing↗