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This study aimed to determine the growth and carbon storage of planted Haloxylon aphyllum in the Aralkum Desert in Kazakhstan. Six sites afforested in 2000, 2005, 2009, 2010, 2013, and 2017 were selected. The root collar diameter (cm) and height (m) were measured for all H. aphyllum in 30 m×44 m plots. Biomass accumulation (g m-2) and carbon storage (C g m-2) were calculated using allometric equations and the carbon concentration data of Haloxylon species. The diameters varied from 2.5 cm to 4.3 cm and the height varied from 106.2 cm to 223.7 cm. The growth of H. aphyllum was not linearly related to the afforestation year or soil properties. Tree growth might have been influenced by variations in the microclimate, such as temperature, precipitation, and dust storms. The mean total biomass accumulation was 20.57 g m-2 and ranged from 2.42 g m-2 to 64.53 g m-2. The mean carbon storage was 9.70 C g m-2 and ranged from 1.12 C g m-2 to 30.61 C g m-2. These biomass and carbon storage estimates were smaller than those reported for other Central Asian deserts, but afforestation enabled the generation of vegetative cover and consequently, carbon sequestration in the manmade Aralkum Desert.

Climate change is likely to decrease surface water availability in Central Asia, thereby necessitating land use adaptations in irrigated regions. The introduction of trees to marginally productive croplands with shallow groundwater was suggested for irrigation water-saving and improving the land’s productivity. Considering the possible trade-offs with water availability in large-scale afforestation, our study predicted the impacts on water balance components in the lower reaches of the Amudarya River to facilitate afforestation planning using the Soil and Water Assessment Tool (SWAT). The land-use scenarios used for modeling analysis considered the afforestation of 62% and 100% of marginally productive croplands under average and low irrigation water supply identified from historical land-use maps. The results indicate a dramatic decrease in the examined water balance components in all afforestation scenarios based largely on the reduced irrigation demand of trees compared to the main crops. Specifically, replacing current crops (mostly cotton) with trees on all marginal land (approximately 663 km2) in the study region with an average water availability would save 1037 mln m3 of gross irrigation input within the study region and lower the annual drainage discharge by 504 mln m3. These effects have a considerable potential to support irrigation water management and enhance drainage functions in adapting to future water supply limitations.

The adverse impacts of ecosystem degradation have raised the need for forest landscape restoration (FLR) to be included in international sustainability agendas. However, the path towards successful FLR implementation faces numerous biophysical, socioeconomic and governance challenges because FLR operates within complex socioecological systems. In the present study, we review and discuss FLR challenges in the context of global environmental change. We propose a roadmap consisting of five interlinked steps to overcome these challenges: (1) advancing ecological knowledge supporting FLR, (2) adapting FLR management to environmental change through strengthening globally distributed experimental networks, (3) implementing modelling approaches, (4) improving socioeconomic and governance dimensions, and (5) developing evidence-based knowledge platforms. The roadmap offers an iterative and adaptive framework for the continuous evaluation and improvement of FLR strategies and outcomes.

Soil degradation in sub-Saharan Africa necessitates accurate soil carbon quantification using a locally applicable method. We assessed the reliability of the original Walkley-Black method for analyzing soil organic carbon (SOC) in semi-arid soils in northern Ethiopia characterized by low SOC (1.3 ± 0.09%) and lack of carbonates. Eighty samples from entire soil profiles were collected in four prevalent land use systems along an elevation gradient and analyzed using the Walkley-Black method and CN elemental analyzer. The results were compared by linear regression analysis followed by the Bland and Altman analysis, eliminating the possible bias of regression. The analyses demonstrated the universal applicability of the Walkley-Black method using the standard correction factor (1.32) for SOC evaluation in carbon-poor, non-calcareous soils.

The design of relevant adaptation strategies for water users in irrigation schemes in the drylands of Sub-Saharan Africa requires up-to-date information about the current performance of these schemes in view of rapid changes in climate and land use, population growth, and competing water demands. Previous assessments focused primarily on field-level crop irrigation; however, information on the performance of schemes as a whole and considering multple water users remains scarce. We examined two (one small- and one medium-scale) irrigation schemes shared by multiple users in the Upper East region of Ghana, including the water reservoir, water conveyance and distribution network, cropping fields, and the management entity. Multi-level performance indicators with relevance to water delivery and utilization as well as to agricultural production during two consecutive dry seasons were used. Technical factors, such as underutilized reservoir storage capacity and deteriorated conditions of water delivery infrastructure, strongly undermined the performance. In particular, the medium-scale irrigation scheme utilized less than 40% of total storage, whereas the small-scale scheme utilized about 70% of the storage. An examination of field-level water management practices suggests that an application efficiency of 58–68% is achievable in both schemes by improving the irrigation scheduling of the major crops. Overall system efficiency can be increased from 50% to 68% by reducing water conveyance network losses and by eliminating over-irrigation of fields. A holistic approach considering all competing water demands is needed for the performance evaluation of reservoir-based irrigation schemes in drylands.

Projected changes in temperature and precipitation in mid-latitude wet regions are expected to significantly affect forest ecosystems. We studied the physiological and shoot growth responses of Abies holophylla and Abies koreana seedlings to warming (3 °C above ambient temperature) and increased precipitation (irrigation with 40% of rainfall) treatments under open-field conditions. The physiological parameters, quantified by the net photosynthetic rate, transpiration rate, stomatal conductance, and total chlorophyll content, were monitored from July to October 2018. Shoot growth (i.e., root collar diameter and height) was assessed in August and December 2018. Irrespective of the treatments, the physiological parameters of both species decreased from July to August under warming treatment due to heat stress before recovering in September and October. Warming alone (W) and warming along with increased precipitation (W*P) decreased the physiological activities of both species in July, August, and September, with more pronounced effects on A. koreana compared with A. holophylla. Increased precipitation resulted in the increased chlorophyll content of both species in October. Shoot growth was not generally affected by the treatments, except for a subtle reduction in height under W*P for A. koreana. A. holophylla had consistently higher values for the physiological parameters and shoot growth than A. koreana. Our results indicate that the physiological activities of the Abies species could be seriously reduced under climate change, with a more severe impact on A. koreana. Among the two species, A. holophylla appears to be a more robust candidate for future forest planting.

Jatropha curcas has been introduced as a low-cost energy crop in Burkina Faso for the production of straight vegetable oil (SVO) and biodiesel. It is cultivated in different plantation systems including smallholder inter-plantings with annual crops, large-scale monoculture, afforestation on marginal land, in traditional hedge systems along contour stone walls, and in living fences. We performed Life Cycle Assessment of these Jatropha systems using empirical data on yields and carbon stocks, and accounting for changes in agro-ecosystem provisioning and regulating services that occurred after the land conversion to Jatropha. The study found that all J. curcas production pathways substantially reduced greenhouse gas emission (68–89%) and saved energy (65–90%) compared to diesel fuel. Highest values are achievable under the assumption that by-products (husks, seed cake, glycerin) are used for energy generation. The decentralized production of SVO supplied by feedstocks from intercropping and hedgerow systems seems to be most promising option. However, very low land-use efficiency (6.5–9.5 GJ ha− 1 production) characterized Jatropha intercropping and monoculture plantations, rendering the plant a competitor to food crops and increasing the risk of conversion of savanna land to Jatropha cultivation. Jatropha plantings on marginal lands largely failed. High labor requirements constrain integration of Jatropha plantation systems within small farmholdings. Currently, the traditional hedge systems show the lowest land-use replacement potential and labor needs while providing multiple ecosystem services, but alone cannot satisfy rural energy needs. In order to reach energy supply targets without claiming more land and compromising other ecosystem services, the J. curcas plantation systems in Burkina Faso need to be made more efficient through plant breeding and improved agronomic management.

Allometric equations are routinely used in the estimation of biomass stocks for carbon accounting within forest ecosystems. However, generic equations may not reflect the growth trajectories of afforestation species that are introduced to degraded farmland characterized by water and nutrient limitations. Using sequential measurements of the height, basal diameter, and above- and belowground biomass of juvenile trees, we developed allometric equations for five woody species (Moringa oleifera Lam., Leucaena leucocephala Lam., Jatropha curcas L., Anacardium occidentale L. and Parkia biglobosa Jacq.) subjected to a gradient of water and nutrient availability in an afforestation trial on degraded cropland in the semi-arid zone of Benin, West Africa. For three of the species studied, the allometric relationships between basal diameter and biomass components (i.e. leaves, stems and roots) were described best by a simple power-law model (R2 > 0.93). The incorporation of species-specific height–diameter relationships and total height as additional predictors in the power-law function also produced reasonable estimates of biomass. Fifteen months after planting, roots accounted for 10–58% of the total biomass while the root-to-shoot ratio ranged between 0.16 and 0.73. The total biomass of the saplings ranged between 1.4 and 10.3 Mg ha−1, yielding 0.6–4.3 Mg C ha−1, far exceeding the biomass in the traditional fallow system. The rate of stem carbon sequestration measured ca. 0.62 Mg C ha−1 year−1. Overall, the allometric equations developed in this study are generally useful for assessing the standing shoot and root biomass of the five afforestation species during the juvenile growth stage and can help in reporting and verifying carbon stocks in young forests.

In the Sudano-Sahelian zone of West Africa, where deforestation and cropland soil degradation occur at alarming rates, the (re-)introduction of trees on degraded lands can improve and sustain farming systems and landscapes. The shoot and root morphological traits of five woody species introduced to degraded cropland were assessed with a particular focus on the survival, early establishment and growth of saplings subjected to manuring (1 kg per plant) and drip irrigation (0.5 L of water per plant per day). Functional traits of the woody above- and belowground organs of field-grown plants were monitored for the first 15 months after planting, covering two growing (rainy) seasons and one dry season. The high survival rate (>60%), combined with a very low incidence rate ( Jatropha curcas L., Leucaena leucocephala Lam. and Moringa oleifera Lam. The mortality rate of the most drought-sensitive species Parkia biglobosa Jacq. could be reduced ten-fold through supplemental irrigation during the dry season. The fast-growing L. leucocephala , M. oleifera and J. curcas had higher values for shoot-level traits than did the slow-growing Anacardium occidentale L. and P. biglobosa . Fertilization and irrigation enhanced the shoot growth of both the fast and slow growers during the dry and growing seasons. In contrast, belowground development was either increased or reduced by fertilization and irrigation during the growing and dry seasons, but the slow growers demonstrated a more plastic response to these treatments than did the fast growers. Among the studied traits, the relative growth rate of plant as a whole (i.e. shoots and roots combined) exhibited the greatest plastic response to resource availability, thus suggesting its application in screening candidate species for afforestation efforts. Overall, the five studied species were considered suitable for the afforestation of degraded croplands, while the early growth and establishment of saplings could be boosted by irrigation and a supply of manure.

This paper presents the theoretical, operational and implementation premises that guide the development research agenda of the Center of Development Research (ZEF), exemplified by three agroforestry-related case studies. First, the importance, assumptions, conditions and priorities for development research in the context of developing countries are reviewed. Second, the three core premises of ZEF’s research approach, (1) transdisciplinary to carry out research on real-life problems, (2) symmetrical partnerships with local stakeholders to sustain ground activities and ensure implementation, and (3) capacity development to warrant future competences, are exposed. Third, these premises are exemplified and mirrored in three agroforestry-related case-studies: (1) slash-and-burn agriculture in the Brazilian Amazon, (2) socio-ecological management of coffee-agroforests in Ethiopia, and (3) afforestation with multipurpose tree species in Uzbekistan. The paper concludes by streamlining the theoretical and practical premises exposed with the presented case-studies, and confirming how these have guided ZEF in the planning, implementation and continuation of development research programs. Although ZEF’s approach to development research is dynamic and continuously subject to assessment, its core remains guiding even after two decades of implementation, appearing to be a suitable pathway for reaching development objectives.

Our study investigated the total terrestrial stock of organic carbon and its controlling factors in prevalent land‐use systems in semi-arid Ethiopia (610 mm of annual rainfall), as part of the impact assessment of the national Integrated Watershed Management (IWM) program. Above- and below-ground biomass and soil organic carbon (SOC) stocks of major land-use systems (i.e., exclosure, cropland, rangeland, and bare land) were quantified after field sampling along a topographic gradient. We found that aboveground carbon stocks peaked in the 15-year-old exclosures (9.08 ± 1.44 Mg ha−1) owing to intact woody and grass vegetation as well as substantial litter cover (>20% of the total biomass). Croplands cultivated with wheat and rangelands vegetated with perennial grasses showed average aboveground carbon stocks of 3.16 ± 0.24 and 1.45 ± 0.19 Mg ha−1, respectively. The belowground biomass carbon stock was particularly low in croplands (0.76 ± 0.09 Mg ha−1), exceeded by that in both exclosures and rangelands, where values averaged 3.67 ± 0.06 and 3.04 ± 0.42 Mg ha−1, respectively. The topsoil (0–30 cm) SOC stocks also varied with land-use systems but showed a different order, peaking in rangelands (53.9 ± 10.1 Mg ha−1) and exclosures (41.4 ± 8.1 Mg ha−1), followed by bare lands (29.0 ± 11.5 Mg ha−1) and croplands (26.4 ± 4.6 Mg ha−1). The sub-soils (30–100 cm) added 40% to this SOC storage. The greatest total SOC stock identified in exclosures that had been established primarily on degraded hillslopes may signify a successful restoration effort under the IWM program. However, croplands exhibited the lowest SOC stock, which implies the need for urgent interventions to improve the soil fertility.

Understanding the complex diversity of species and their potential uses in traditional agroforestry systems is crucial for enhancing the productivity of tropical systems and ensuring the sustainability of the natural resource base. The aim of this study is the evaluation of the role of home gardens and parklands, which are prominent tropical agroforestry systems, in the conservation and management of biodiversity. Our study quantified and compared the diversity of woody and herbaceous perennial species and their uses in traditional home gardens and parkland agroforestry systems under a sub-humid climate in western Ethiopia. A sociological survey of 130 household respondents revealed 14 different uses of the species, mostly for shade, fuelwood, food, and as traditional medicine. Vegetation inventory showed that the Fisher&rsquo, s &alpha, diversity index and species richness were significantly higher in home gardens (Fisher&rsquo, = 5.28 &plusmn, 0.35) than in parklands (Fisher&rsquo, = 1.62 &plusmn, 0.18). Both systems were significantly different in species composition (S&oslash, renson&rsquo, s similarity coefficient = 35%). The differences occurred primarily because of the high intensity of management and the cultivation of exotic tree species in the home gardens, whereas parklands harbored mostly native flora owing to the deliberate retention and assisted regeneration by farmers. In home gardens, Mangifera indica L. was the most important woody species, followed by Cordia africana Lam. and Coffea arabica L. On the other hand, Syzygium guineense Wall. was the most important species in parklands, followed by C. africana and M. indica. The species diversity of agroforestry practices must be further augmented with both indigenous and useful, non-invasive exotic woody and herbaceous species, particularly in parklands that showed lower than expected species diversity compared to home-gardens.

Global warming is predicted to increase water scarcity in many drylands worldwide. In Central Asia, one of the most intensively irrigated dryland agricultural regions, climate change is likely to exacerbate the regional water supply–demand gaps, particularly in downstream areas. The withdrawal of degraded, highly salinized croplands from irrigated farming in favor of tree plantations that effectively utilize saline groundwater may contribute to irrigation water saving, which can generate valuable ecosystem services and provide rural income opportunities. To facilitate the spatial planning of afforestation in the lower Amudarya region, we developed a hydrological algorithm to map the spatio-temporal pattern of water supply–demand. The resulting map, based on seven-year continuous data of cropping pattern and corresponding irrigation dynamics, rainfall, and evapotranspiration at 250 m resolution, revealed the overly irrigated areas from which excess water can be redistributed to water-stressed areas. Furthermore, combining this information with spatial data on marginally productive croplands and with water requirement of tree plantations showed that 67% of these croplands are characterized by water availability sufficient for the introduction of salt-tolerant tree species. The algorithm developed is of potential use for defining the feasibility of introducing alternative (tree) crops with known growth and water use characteristics.

The early growth stage is critical in the response of trees to climate change and variability. It is not clear, however, what climate metrics are best to define the early-growth sensitivity in assessing adaptation strategies of young forests to climate change. Using a combination of field experiments and modelling, we assessed the climate sensitivity of two promising afforestation species, Jatropha curcas L. and Moringa oleifera Lam., by analyzing their predicted climate&ndash, growth relationships in the initial two years after planting on degraded cropland in the semi-arid zone of Benin. The process-based WaNuLCAS model (version 4.3, World Agroforestry Centre, Bogor, Indonesia) was used to simulate aboveground biomass growth for each year in the climate record (1981&ndash, 2016), either as the first or as the second year of tree growth. Linear mixed models related the annual biomass growth to climate indicators, and climate sensitivity indices quantified climate&ndash, growth relationships. In the first year, the length of dry spells had the strongest effect on tree growth. In the following year, the annual water deficit and length of dry season became the strongest predictors. Simulated rooting depths greater than those observed in the experiments enhanced biomass growth under extreme dry conditions and reduced sapling sensitivity to drought. Projected increases in aridity implied significant growth reduction, but a multi-species approach to afforestation using species that are able to develop deep-penetrating roots should increase the resilience of young forests to climate change. The results illustrate that process-based modelling, combined with field experiments, can be effective in assessing the climate&ndash, growth relationships of tree species.

We evaluated the annual stocks and decay rates of leaf litter, green foliage, and fine roots at a multiple-species afforestation site using the litterbag technique over 3 years. During the course of each year the decomposition of all residue types exhibited a pattern of initially rapid loss of mass over winter followed by decomposition rates that were effectively zero for the rest of the year. Depending on the year of measurement and tree species, decay constants defined by the asymptotic function (k a ) for foliar materials ranged between 3 and 16 year−1, with 55–74 % of the initial mass remaining after 1 year of field exposure. The greatest amount of mass remaining was observed in the third year when topsoil salinity increased to a point (11–18 dS m−1) that it inhibited decomposition, superseding the influences of species characteristics and soil moisture. For foliar materials, the remaining stable fraction was smaller in Elaeagnus angustifolia that also showed a slower decay rate than other species. Fine roots (at a depth of 30 cm) degraded faster in all species, with 33–38 % of the initial mass remaining. The decay rates were lowest for Ulmus pumila roots, which were characterized by relatively dense tissue. The greater production and decomposition of nitrogen-rich residue might explain the superior performance of E. angustifolia in improving saline soil productivity. Irrespective of species, the carbon returns through the relatively fast decomposition of fine roots benefit soil fertility, whereas large inputs of slowly decomposing foliar residues represent carbon sequestration in the aboveground litter pool.

Our study addressed biomass dynamics in traditional and newly introduced Jatropha curcas production systems in Burkina Faso, West Africa. Five prevailing J. curcas systems included interplanting with annual crops, intensely managed plantations, afforestation of abandoned land, plantings along contour stone walls, and traditional living fences. Measurements of stem diameter, tree height (n = 670) and above- and below-ground biomass (n = 157) enabled the development of generic allometric models relating shoot and root biomass with stem diameter. The relations showed very good fits (R 2 > 0.9) for all studied systems, except afforestation sites which largely perished. Considering system-specific height-diameter (HD) relationship improved the model performance for living fences where trees allocated more biomass in the height rather than diameter growth. Self-propagation in living fences results in variable stand density, tree age, and consequently shifting HD relations. Therefore these models would benefit from local calibrations should they be applied elsewhere. We argue that for the other systems the developed generic equations are applicable subject to accounting for the tree ontogenetic stages deduced from HD relations. In this respect, the allometric models for juvenile trees are most robust whereas overall validity range of the equations can be improved with more observations of large-size trees.

Acquiring multi-temporal spatial information on vegetation condition at scales appropriate for site-specific agricultural management is often complicated by the need for meticulous field measurements. Understanding spatial/temporal crop cover heterogeneity within irrigated croplands may support sustainable land use, specifically in areas affected by land degradation due to secondary soil salinization. This study demonstrates the use of multi-temporal, high spatial resolution (10 m) SPOT-4/5 image data in an integrated change vector analysis and spectral mixture analysis (CVA-SMA) procedure. This procedure was implemented with the principal objective of mapping sub-field vegetation cover dynamics in irrigated lowland areas within the lowerlands of the Amu Darya River. CVA intensity and direction were calculated separately for the periods of 1998–2006 and 2006–2010. Cumulative change intensity and the overall directional trend were also derived for the entire observation period of 1998–2010. Results show that most of the vector changes were observed between 1998 and 2006; persistent conditions were seen within the study region during the 2006–2010 period. A decreasing vegetation cover trend was identified within 38% of arable land. Areas of decreasing vegetation cover were located principally in the irrigation system periphery where deficient water supply and low soil quality lead to substandard crop development. During the 2006–2010 timeframe, degraded crop cover conditions persisted in 37% of arable land. Vegetation cover increased in 25% of the arable land where irrigation water supply was adequate. This high sub-field crop performance spatial heterogeneity clearly indicates that current land management practices are inefficient. Such information can provide the basis for implementing and adapting irrigation applications and salt leaching techniques to site-specific conditions and thereby make a significant contribution to sustainable regional land management.

Agroforestry is often an economically viable land-use option for the environmental rehabilitation of salinized cropping areas in irrigated drylands, but afforestation initiative at the farm level is subject to various socio-political constraints. We analyzed the factors that affect farmer decisions with respect to the agroforestry adoption using an ex ante approach through Ethnographic Decision Tree Modeling (EDTM). Constraints on agroforestry adoption were identified via a review of legal documents, focus-group discussions, and a farm survey in northwest Uzbekistan. The findings highlighted the importance of farmer perceptions of risk with respect to decision making surrounding the adoption of alternative land uses. The EDTM analysis allowed determining those policy incentives for afforestation that could directly influence the decision-making process of potential participants. In particular, there is a need for increased land-use flexibility, improved land tenure and tree plantation proprietorship secur...

The changes in the relative biomass allocation to roots in juvenile stands of fast-growing ( Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L.) and slow-growing ( Anacardium occidentale L. and Parkia biglobosa Jacq.) afforestation species are driven mainly by ontogeny rather than resource availability. However, silvicultural management aiming at increasing availability of water and particularly nutrients enhances biomass production in all species. Understanding the patterns of biomass allocation among tree species in response to ontogeny and to variation in resource availability is key to the successful restoration of degraded land using forest plantations. This study assessed the effects of resource availability and ontogeny on biomass accumulation and partitioning in five semi-arid afforestation species. The aboveground and belowground biomass production of fast-growing Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L. and slow-growing Anacardium occidentale L. and Parkia biglobosa Jacq. was monitored following the application of manure (1 kg plant−1) and/or supplemental irrigation (0.5 L per sapling daily) during the first two rainy seasons and the intervening dry season on degraded cropland in Northern Benin. Biomass accumulation in the fast-growing species was positively impacted by fertilization and irrigation during both rainy seasons. The slow-growing species responded positively to the silvicultural treatments during the dry and second rainy season. The application of fertilizer alone increased the biomass of P. biglobosa by up to 335% during the dry season. Fifteen months after planting, manure-treated L. leucocephala accumulated the most biomass (2.9 kg tree−1). The root fraction decreased with increasing tree size in all species. The comparison of root versus shoot allocation in trees of equal size indicated that the treatment-induced shifts in biomass partitioning were controlled by ontogeny, which explained 86–95% of the variation in root-shoot biomass relationships. While ontogeny was the main driver of biomass partitioning, increased resource availability induced a larger production of biomass, overall leading to greater aboveground production in all species.

We analysed the economic viability of afforestation on marginal irrigated croplands in irrigated drylands of Uzbekistan. The revenues derived from a combination of diversified agricultural production, carbon sequestration, nitrogen fixation, and avoided irrigation water use were analysed considering uncertainty associated with on-farm activities such as crop production and short-rotation forestry. At the per hectare scale variability in land-use revenues would necessitate substantial increases in carbon prices for afforestation to be as profitable as crop cultivation on marginal lands, assuming an abundant irrigation water supply. In contrast, at the farm scale the analysis results revealed that afforestation can be attractive financially even without carbon payments due to farm production constraints, variable land-use returns, and the benefits of land-use diversification. Increased carbon prices would promote carbon sequestration by motivating farmers to plant high biomass producing tree species, but would have an ecosystem service trade-off by reducing the appeal of nitrogen-fixing species that are essential for nitrogen self-sufficiency of afforestation efforts. Given the modest irrigation needs of afforestation efforts compared to the cultivation of annual crops, tree plantations could become a primary income source for farms during periods of drought. Irrigation water saved from replacing crops with trees on marginal farmland would enhance the cultivation of commercial crops on productive lands, thus increasing farm income.

Degradation of irrigated croplands in arid regions is of great environmental concern worldwide. Based on a series of field trials, afforestation with well-adapted tree species was evaluated as a viable option for the cropland rehabilitation in the lower reaches of the Amudarya River basin in Uzbekistan. Our aim was to extend available site-specific information for the entire regional landscape and provide spatially explicit guidance in support of afforestation land rehabilitation efforts. To this end, a geographic information system—based multicriteria decision-making approach has been developed for assessing the suitability of degraded irrigated cropland for introducing plantations of Elaeagnus angustifolia L. This approach utilized expert knowledge, fuzzy logic, and a weighted linear combination to produce an afforestation land suitability map. Overall, 75 287 ha of degraded croplands (18% of the irrigated cropland area) was identified as suitable for introduction of E. angustifolia. We also conclude that irrigation water supply and groundwater table depth are the critical factors determining the suitability of degraded irrigated land. These findings improve an understanding of the spatial variability of areas suitable for the initiation of agroforests and support better informed decisions on cropland rehabilitation. Copyright © 2014 John Wiley & Sons, Ltd.

The cultivation of the biofuel crop Jatropha curcas L. in Burkina Faso may contribute to ameliorating the soil fertility of severely declining cropland through increased organic matter input and erosion control. This study addresses the potential for the soil organic carbon (SOC) sequestration in traditional and newly introduced J. curcas production systems. Five prevailing systems included interplanting with annual crops, intensely managed monoculture plantations, afforestation of abandoned cropland, plantings along contour stone walls, and traditional living fences. The SOC was analyzed in 20 paired sites of 1- to 4-year-old J. curcas plantings and adjacent cropland. Paired sites with living fences involved a longer chronosequence with 15- and 20-year-old plantings. Additionally, the contribution of J. curcas to SOC sequestration was investigated by comparing the 13C signature of the C inputs in four J. curcas sites with that of sorghum cropping. Linear regression analysis did not reveal a clear trend of SOC dynamics over time for the short-term chronosequences, nor could the isotopic tracer technique prove a contribution of 4-year-old J. curcas trees to the SOC stock. The 20-year chronosequence of J. curcas living fences exhibited a significant SOC increase of 62 ± 23 g m−2 y−1. Considering soil coverage of 1,200 m2 ha−1 by living fences (400-m hedge with a width of 3 m), 1.5 Mg SOC was sequestered. Also, changes in δ13C values indicated a contribution of C3-derived C to the SOC stock. These findings on traditional J. curcas systems indicate the potential of this biofuel crop for improving cropland soil fertility in the long run. Copyright © 2014 John Wiley & Sons, Ltd.

Afforestation is known as a low-input measure to rehabilitate marginalized irrigated croplands with a shallow, saline groundwater table. This study assessed the potential of extending afforestation to sites long-term abandoned from cropping in the lower reaches of the Amu Darya River, Central Asia. Tree survival and establishment were monitored during two growing seasons following afforestation with six tree species at two abandoned cropping sites. The sites, characterized by soil salinity and different depth to the groundwater table, received deficit irrigation of 154 mm yr−1. Afforestation was feasible with Elaeagnus angustifolia, Ulmus pumila, Morus alba, and Populus nivea x tremula given their survival rates of 75–91% on both sites after two years. N2-fixing E. angustifolia was assessed as most promising among all species evidenced by highest survival and largest above-ground biomass increment (up to 904 kg ha−1 yr−1). The principal species of the native floodplain forest, Populus euphratica and Salix...

The desiccation of the Aral Sea due to water withdrawal from contributing rivers has resulted in an unprecedented change in the region’s climate, from maritime to hot dry desert. Afforestation has been implemented on the desiccated seafloor—the Aralkum Desert—for stabilizing the exposed substrate. However, studies on the long-term status of the afforested sites are limited. Here, we examined C and N isotopic signatures in Haloxylon aphyllum plantations, as indicators of time-integrated plant response to the prevalent water and salinity constraints, in northern Aralkum, Kazakhstan. Foliar 13C composition analysis in a chronosequence of H. aphyllum plantation sites (aged 1−27 years) on the sandy substrate revealed a significant trend towards higher water-use efficiency in older plantations, possibly in response to declining water availability. A lack of correlation between plant 13C signature and soil electrical conductivity suggests no history of salt stress despite the saline environment. Furthermore, 15N enrichment in plant tissue in the water-limited Aralkum ecosystem indicates the relative openness of N cycling. There was an increase in species richness and self-propagation at the plot scale, indicating successful afforestation effort. Coupled with other approaches, isotope discrimination might elucidate mechanisms underlying stress tolerance in H. aphyllum, which could support the afforestation efforts.

The conversion of marginal croplands to tree plantations, as an option to address climate change, land degradation, and irrigation water scarcity, as well as to improve the welfare of local population requires prior analysis. This study analyzed the impacts of afforestation of marginal croplands, including potential benefits in the form of carbon sequestration rewards via the Clean Development Mechanism, on the livelihood of commercial farms and rural households by considering their interdependencies via wage-labor relations in irrigated agricultural regions of the lower reaches of the Amu Darya River, Central Asia. A dynamic nonlinear programming model was developed that jointly maximizes profit of farm and net incomes of rural households over a 15-year horizon under conditions of decreasing irrigation water availability and forestry plantations with a single seven-year rotation period. The results showed that the introduction of short-rotation plantation forestry in degraded irrigated croplands can help mitigate the repercussions of water shortages on rural livelihood, while sustaining energy needs, income, and food security. Although income and food consumption of rural households may decline from year two to six after afforestation, the subsequent increase in farm profit following the harvest of tree plantations would be transmitted to rural households through existing wage-labor payment arrangements. The incorporation of fuelwood into labor payment schemes would substitute the use of fossil fuels by rural households and thus substantially decrease their energy expenses and CO2 emissions. Furthermore, given the low irrigation water demand of trees, afforestation would increase irrigation water availability for more productive croplands.

Irrigated croplands of Central Asia are highly prone to land degradation due to their fragile physical settings and extensive agricultural land use. Current remote-sensing data and spatio-temporal analyses allow for detecting regional trends in a land decline and for relating them to underlying factors which is important for developing mitigation strategies. This study aimed to (1) assess the cropland’s state in the large irrigated agricultural areas in the northern Uzbekistan based on the time series of MODIS NDVI images, (2) relate the degradation trend to its factors including soil quality, terrain, population density and land use, and (3) synthesize the results to provide recommendation on spatial targeting of land rehabilitation measures. An NDVI-based land degradation assessment revealed a significant decline of land productivity across 23.13% (94834.90 ha) of the arable area in the study region. The degraded cropland, located in the areas of high population pressure and characterized by better-quality soils, should be prioritized for rehabilitation measures. For the degraded cropland, found on the poor-quality soils and in the areas of low population density, depending on the severity of degradation, a decision has to be made whether to vacant the land from agriculture or to continue cultivation if the latter is an economically viable option.

Afforestation of degraded croplands by planting N2-fixing trees in arid regions is highly recognized. However, fixation of atmospheric nitrogen gas (N2) by woody perennials is often limited on phosphorus (P) poor soils, while any factor limiting N nutrition inhibits tree growth. In a two-factorial field experiment, the effect of three P amendments was examined during 2006–2008 on N2 fixation, biomass production, and foliage feed quality of actinorhizal Elaeagnus angustifolia L. and leguminous Robinia pseudoacacia L. With the 15N natural abundance method, N2 fixation was quantified based on foliar and whole-tree sampling against three non-N2-fixing reference species: Gleditsia triacanthos L., Populus euphratica Oliv., and Ulmus pumila L. The P applications, in March 2006 and April 2007 only, included (i) high-P (90 kg P ha−1), (ii) low-P (45 kg P ha−1), and (iii) 0-P. After 3 years, the average proportion of N derived from atmosphere (Ndfa, %) increased from 78 % with 0-P to 87 % with high P when confounded over both N2-fixing species. With the used density of 5,714 trees ha−1, the total amount of N2 fixed (Ndfa, kg N ha−1) with high-P increased from 64 kg N ha−1 (year 1) to 807 kg N ha−1 (year 3) in E. angustifolia and from 9 kg N ha−1 (year 1) to 155 kg N ha−1 (year 3) in R. pseudoacacia. Total above-ground biomass increases were too variable to be significant. Leaf N content and therewith also leaf crude protein content, which is an indicator for feed quality, increased significantly (24 %) with high-P when compared to 0-P for E. angustifolia. Overall findings indicated the suitability of the two N2-fixing species for afforestating salt-affected croplands, low in soil P. With P-applications as low as 90 kg P ha−1, the production potential of E. angustifolia and R. pseudoacacia, including the supply of protein-rich feed, could be increased on salt-affected croplands.

Agricultural mismanagement of irrigated drylands results in severe soil degradation. Afforestation is an option for ameliorating such degraded land. We evaluated the impact afforestation has on the topsoil (0–20 cm) of salinized degraded cropland in regards to salinity, aggregate stability, and soil organic carbon (SOC) stocks in Uzbekistan, Central Asia. The effects of tree plantations established under either furrow or drip irrigation were studied four years following afforestation and two years after irrigation ceased. For comparative study we also sampled fallow land, land with 80 years of tree growth, natural forest, desert ecosystems, and paddy rice fields. Initial furrow irrigation showed to be most effective in improving soil fertility after four years of afforestation; the respective plantations of Populus euphratica and Ulmus pumila showed significant levels of reduced soil salinity and increased aggregate stability and improved SOC stocks. The comparison of the long-term afforested land with the short-term equivalent suggested a C sequestration rate of 0.09–0.15 t C ha −1 year −1 . The SOC stocks of the long-term afforestation site exceeded those of the native forest. Hence, a rehabilitation of salt-affected cropland is feasible following the conversion into occasionally irrigated tree plantations, although it takes decades to reach steady-state conditions.

Ground based dust monitoring is an important tool for the long-term monitoring of aeolian sediment transport in Central Asia as it provides valuable insights into the spatial and temporal dynamics of dust deposition as well as grants access to the transported material for further analyses. Between 2006 and 2012 such a monitoring was carried out in the Turan lowland to analyze the effects of the newly formed Aralkum. The detected spatial and temporal dust deposition variability was significant and encourages further studies. The dust deposition increased over time, which correlates with a decreasing trend in precipitation, increasing wind speeds and a shift towards northern winds. More than 50% of all dust samples collected exceed the health based deposition threshold and the most intense dust storm events reached ground level deposition rates of up to 150 g/m2 per hour. This study showed the impact of the Aralkum, but also that the Kyzylkum is a far more active dust source. With regard to climate change and an increasing aridity in the region it can be expected that the aeolian dust transport will continue to increase, making a wide-spread monitoring program even more important.

Feed shortages hamper livestock rearing and thus impede the development of rural livelihoods in Central Asia. The production and in vitro quality of foliage from Ulmus pumila, Elaeagnus angustifolia and Populus euphratica on degraded cropland were examined to determine the potential of these species to supplement diary cattle diets. Leaf dry matter (DM) production of the species, respectively, averaged 6, 8 and 17 t DM/ha, 4 years after planting. Over seasons and years, crude protein concentrations (g/kg DM) ranged within 151-257 for E. angustifolia, 70-241 for U. pumila and 92-187 for P. euphratica. The metabolizable energy concentrations (MJ/kg DM) were the highest in U. pumila and ranged within 9-10, followed by 7-10 of E. angustifolia and 7-9 of P. euphratica. The organic matter digestibility (%) ranged within 58-70, 54-66, and 51-66, respectively, for these species. These indicators combined denoted a medium-to-good feed quality of E. angustifolia and U. pumila leaves as a cheap protein supplement to roughages. The foliage of P. euphratica was the least suitable. The seasonal profile of in vitro indicators revealed the highest feed quality in spring but early fall seems most appropriate for forage collection given the peak leaf production and an adequate quality.

Improving irrigation management in semi-arid regions of Sub-Saharan Africa is crucial to respond to increasing variability in rainfall and overcome deficits in current irrigation schemes. In small-scale and medium-scale reservoir-based irrigation schemes in the Upper East region of Ghana, we explored options for improving the traditional, dry season irrigation practices and assessed the potential for supplemental irrigation in the rainy season. The AquaCrop model was used to (i) assess current water management in the typical tomato-maize rotational system; (ii) develop an improved irrigation schedule for dry season cultivation of tomato; and (iii) determine the requirement for supplemental irrigation of maize in the rainy season under different climate scenarios. The improved irrigation schedule for dry season tomato cultivation would result in a water saving of 130–1325 mm compared to traditional irrigation practices, accompanied by approximately a 4–14% increase in tomato yield. The supplemental irrigation of maize would require 107–126 mm of water in periods of low rainfall and frequent dry spells, and 88–105 mm in periods of high rainfall and rare dry spells. Therefore, year-round irrigated crop production may be feasible, using water saved during dry season tomato cultivation for supplemental irrigation of maize in the rainy season.

Afforestation with fast growing N-fixing trees is an option for ecological restoration of highly-salinized irrigated croplands, but information about the N-fixing capability of trees on saline soils is sparse. The 15N-enrichment technique (15NET) and the A value (AV) method were used to quantify in lysimeters the proportion of atmospheric N2 (%Ndfa) fixed by Elaeagnus angustifolia L., with a reference to non-N-fixing Gleditsia triacanthos L. and Ulmus pumila L. Twenty kg N ha−1 of 5 atom %15N excess ammonium nitrate (35% N) was applied to 1-year-old trees in 2007 and 2-year-olds in 2008. Since this rate was insufficient for the older reference trees, 60 kg N ha−1 was applied in 2008. With 15NET, the %Ndfa of E. angustifolia in 2007 was 79% when referenced against U. pumila and 68% against G. triacanthos. With the AV method, the %Ndfa of 2-year-old E. angustifolia was 80 and 68% when referenced against U. pumila and G. triacanthos, respectively. Over 2 years, E. angustifolia fixed 17 kg N ha−1 when related to U. pumila and 14 kg N ha−1 with G. triacanthos (assumed density: 5,000 trees ha−1). N-fixing E. angustifolia has the potential to be self-sufficient in N when planted in the strongly saline soils.