Land Degradation In Drylands Research Articles

Ecological improvement of takyric solonetz in northern China using modified ridge cultivation with drip irrigation

AbstractSoil salinization is one of the most important forms of land degradation in drylands of the world. As a typical type of saline‐sodic soil, takyric solonetz seriously jeopardizes the living environment of the inhabitants with severe consequences for regional ecology, agriculture, and the aeolian dust dynamics. Improving the vegetation and ecology status of takyric solonetz is essential but challenging because of its extremely drought conditions with low saturated hydraulic conductivities (ks <0.1 mm/day). Here, we conducted a three‐year field experiment by three‐stage drip irrigation to regulate the water and salt levels of the soil and improved ridge cultivation through sand as a water dispersal media strip for takyric solonetz in northern China. Results showed that the planting ridge was desalted after 3‐year treatments of drip irrigation. The electrical conductivity of a saturated soil paste extract reduced from 21.28 and 13.38 to below 3.00 dS/m, indicating a decrease of 91.50% and 88.50% in the 0–40 cm and 0–120 cm soil layers, respectively. The pH of the soil paste extract decreased from 11.13 to 9.78 in the 0–120 cm soil layer. The survival rate of the willow saplings planted for a shelterbelt was 91.60%. The height, diameter at breast height, and ground diameter of the willow increased slowly to 84.60 cm, 1.20 mm, and 2.02 mm in the first 2 years, respectively, but increased rapidly to 121.90 cm, 7.48 mm, and 12.02 mm, respectively, in the third year. Our treatment also substantially changed the understory vegetation status, in terms of vegetation coverage (89%), number of species (18), and density (600 plant m−2). The dominant plant family in the vegetation community shifted from the Amaranthaceae to the Poaceae. This study provides and validates a new technology for ecological improvement of takyric solonetz, supporting a theoretical and practical approach for ecosystem and vegetation improvement in takyric solonetz in the future.

Comprehensive assessment of land degradation in the arid and semiarid area based on the optimal land degradation index model

Paying attention to land degradation in drylands is of international significance because it plays a crucial role in global food production. This study developed the optimal land degradation index (OLDI) model for arid and semiarid areas. The model utilized a system that assessed soil condition, climate response, human disturbance, and vegetation growth. It was based on a constrained optimization algorithm. Based on the analysis of the distribution pattern of the OLDI in the Hexi Corridor, this study aims to explore the spatial and temporal characteristics of land degradation and the variations in land sensitivity to degradation across different seasons through trend analysis. Furthermore, the main variables that control the environment and are responsible for land degradation or improvement were revealed through the analysis of driving factors. It was found that the oasis areas in the southern part of the Hexi Corridor experienced land improvement due to the combined influence of human activities and climate change, while the northern region underwent continuous land degradation. However, overall, the majority of the study area's land remained stable. The reduction in precipitation and the increase in wind speed were identified as the primary driving forces behind land degradation. Different vegetation types exhibited distinct responses to environmental control factors, and these responses varied significantly with the changing seasons. Based on the regional variations in land degradation and the observed sensitivity characteristics during different seasons, this study proposes a land management strategy that combines natural recovery with artificial restoration to achieve effective prevention, control, and management of land degradation. This study provided an effective tool for monitoring land degradation in arid and semiarid areas, which is of significant importance for land resource management and the sustainable development of the green economy, not only in the northwest region of China but also in arid and semiarid areas worldwide.

Bibliometric Analysis of Land Degradation Studies in Drylands Using Remote Sensing Data: A 40-Year Review

Drylands are vast and face threats from climate change and human activities. Traditional reviews cannot capture interdisciplinary knowledge, but bibliometric analysis provides valuable insights. Our study conducted bibliometric research of scientific production on climate change and land degradation in drylands using remote sensing. We examined 1527 Scopus-indexed publications to identify geographic and thematic hotspots, extracting leading authors, journals, and institutions. China leads in publications, followed by the US, Germany, and Australia. The US has the highest citation count. Collaboration networks involve the US, China, and European countries. There has been an exponential increase in remote sensing of land degradation in drylands (RSLDD) publications since 2011. Key journals include “International Journal of Remote Sensing” and “Remote Sensing of Environment”. The analysis highlights the growing interest in the field, driven by Australia, the US, and China. Key areas of study are vegetation dynamics and land use change. Future perspectives for this scientific field involve promoting collaboration and exploring emerging technologies for comprehensive land degradation and desertification research.

Water and wind erosion response to ecological restoration measures in China's drylands

Soil erosion is the most severe form of land degradation threatening terrestrial ecosystems globally. Drylands with fragile ecosystems are particularly sensitive to soil erosion. China's drylands face the threat of soil erosion by wind and water. Currently, more studies need to be focused on wind and water erosion response to ecological restoration measures at monthly resolution in these areas. This is key to understanding ecological restoration measures' effectiveness under changing environments. Here, we assessed the monthly water and wind erosion in China's drylands from 2001 to 2020 using the G2 model and revised wind erosion equation (RWEQ). The Sequential linear regression slopes (SeRGS) explored water and wind erosion intensities. We also discuss the mitigation benefits of two ecological restoration measures, afforestation and grassland restoration. The results showed that water and wind erosion in China's drylands is mild (47.35%) and slight (58.76%). Water erosion increased between 2001 and 2020, while wind erosion decreased. At the monthly level, a higher water and wind erosion rate occurred from April to June and February to March, respectively. Water erosion dominated 50.64% of the China's drylands, while wind erosion was the most critical form of erosion in 47.88%. Nevertheless, the erosion pattern in China's drylands is changing. The average mitigation benefits of afforestation on water and wind erosion were −61.12% and −57.05%, respectively, and the average mitigation benefits of grassland restoration on water and wind erosion were −57.05% and 7.95%, respectively. This study can help managers identify the best ecological restoration strategies to mitigate land degradation in drylands.

Recent climatological conditions and land degradation in drylands

Recent climatological conditions and land degradation in drylands

Plantation soil inoculation combined with straw checkerboard barriers enhances ectomycorrhizal colonization and subsequent growth of nursery grown Pinus tabulaeformis seedlings in a dryland

Aeolian desertification is the dominant form of land degradation in drylands. The straw checkerboard barrier (SCB) method is effective for sand fixation and has been used to combat aeolian desertification in China. Soil inoculation with ectomycorrhizal (ECM) fungi can help restore degraded lands by improving the soil microbial community and steering plant community development. Combining SCB with afforestation via planting ECM trees and inoculating soil with ECM fungi holds promise for improving plant establishment and growth on shifting sand dunes, but this has yet to be examined. Here, we tested the effects of soil inoculation on ECM colonization of Pinus tabulaeformis roots and the survival and establishment of nursery grown P. tabulaeformis seedlings using three soil treatments: no soil (NS), soil sterilized with fungicide (FPS), and ECM-containing non-treated plantation soil (NPS) collected from a nearby P. tabulaeformis plantation. After two years, P. tabulaeformis survival did not differ among the three soil treatments, but ECM colonization rate, total plant dry weight, and leaf total nitrogen per one seedling in the NPS treatment were 9.0, 2.6, and 3.4 times higher than those in the NS treatment. Water use represented by leaf δ13C was also highest in the NPS treatment. Structural equation modeling showed that soil inoculation enhanced ECM colonization of P. tabulaeformis, thus improving nitrogen uptake and water use, leading to increased plant growth. Suillus, Peziza, Geopora, Tuber, and Tomentella were the dominant genera in NPS treatment; 94% of the ECM roots in the NPS treatment were colonized by ECM fungi not detected in NS treatment, indicating that ECM fungi from the inoculum soil were able to colonize the roots of nursery grown seedlings. Only a few ECM fungal species could colonize P. tabulaeformis roots from the plantation soil inoculated, but the taxonomic diversity including Basidiomycota and functional diversity of mycelial exploration types were increased by soil inoculation. These results suggest that soil inoculation with ECM fungi aids in afforestation with ECM plants for the restoration of degraded drylands, including shifting sand dunes.

Exopolysaccharide Features Influence Growth Success in Biocrust-forming Cyanobacteria, Moving From Liquid Culture to Sand Microcosms.

Land degradation in drylands is a drawback of the combined action of climate change and human activities. New techniques have been developed to induce artificial biocrusts formation as a tool for restoration of degraded drylands, and among them soils inoculation with cyanobacteria adapted to environmental stress. Improvement of soil properties by cyanobacteria inoculation is largely related to their ability to synthesize exopolysaccharides (EPS). However, cyanobacterial EPS features [amount, molecular weight (MW), composition] can change from one species to another or when grown in different conditions. We investigated the differences in growth and polysaccharidic matrix features among three common biocrust-forming cyanobacteria (Nostoc commune, Scytonema javanicum, and Phormidium ambiguum), when grown in liquid media and on sandy soil microcosms under optimal nutrient and water, in controlled laboratory conditions. We extracted and analyzed the released EPS (RPS) and sheath for the liquid cultures, and the more soluble or loosely-bound (LB) and the more condensed or tightly-bound (TB) soil EPS fractions for the sandy soil microcosms. In liquid culture, P. ambiguum showed the greatest growth and EPS release. In contrast, on the sandy soil, S. javanicum showed the highest growth and highest LB-EPS content. N. commune showed no relevant growth after its inoculation of the sandy soil. A difference was observed in terms of MW distribution, showing that the higher MW of the polymers produced by P. ambiguum and S. javanicum compared to the polymers produced by N. commune, could have had a positive effect on growth for the first two organisms when inoculated on the sandy soil. We also observed how both RPS and sheath fractions reflected in the composition of the soil TB-EPS fraction, indicating the role in soil stabilization of both the released and the cell attached EPS. Our results indicate that the features of the polysaccharidic matrix produced by different cyanobacteria can influence their growth success in soil. These results are of great relevance when selecting suitable candidates for large-scale cyanobacteria applications in soil restoration.

Applying Geodetector to disentangle the contributions of natural and anthropogenic factors to NDVI variations in the middle reaches of the Heihe River Basin

Abstract The detection and attribution of vegetation changes is a prerequisite for vegetation restoration and management. In arid and semi-arid areas, natural and anthropogenic factors interact to influence vegetation change, making it challenging to disentangle the contributions of driving forces. Here we used NDVI as an indicator of vegetation condition and analyzed its spatial and temporal changes in the middle reaches of the Heihe River Basin from 2000 to 2015. Then we applied the Geodetector method, a robust spatial statistics approach, to quantify the effects of natural and anthropogenic factors on NDVI changes. NDVI across the study area showed a significant increasing trend from 2000 to 2015. Both natural and anthropogenic factors were identified as significant driving forces of NDVI change, and the factors, land use conversion type, mean annual precipitation and soil type, caused the greatest influence. The explanatory power of a single factor was often enhanced when it interacted with other factors. We also found that influencing factors often correlated with NDVI changes in a non-linear way. Our research highlights that the Geodetector method is an effective way to disentangle the complicated driving factors of vegetation change, and our results is useful for projecting vegetation change under future environmental change and taking measures to prevent and mitigate land degradation in drylands.

Ecological effects of establishing a 40-year oasis protection system in a northwestern China desert

Oasis-protection systems are created globally to reverse land degradation in drylands and improve ecosystem condition. This study assessed the effects of a 40-year oasis-protection system on soil physicochemical and plant community properties along a gradient from prohibited grazing to fenced shrublands, to shrub- and tree plantation belts in arid northwestern China. We found that compared with shifting dunes in unprotected desert settings, the wind velocity and sand transportation rate decreased by 75 and 98% when spring storms passed through the most protected shrub- and tree- plantations in the oasis-protection system, respectively. The fraction of silt and clay content, and soil carbon, total nitrogen, and total phosphorus significantly increased along the protection gradient, and reached their highest levels at the most protected belts. Meanwhile, an annual herbaceous plant community developed, and the densities, covers, and biomasses of herbaceous plant species increased with soil nutrients along the gradient. However, a significant increase in soil salinity, sodicity, and desiccation occurred at the shrub- and tree plantation belts, and shrub and tree species introduced in the plantations failed to regenerate after 40 years. Our results demonstrate that the positive effects of oasis-protection systems need to be weighed against the long-term negative consequences of soil salt accumulation and desiccation that can occur in frequently used shrub- and tree plantations, which limits future plant regeneration and ecosystem recovery.

Detailed land use transition quantification matters for smart land management in drylands: An in-depth analysis in Northwest China

Due to the lack of smart land management strategies, the rapid expansion of cultivated oases usually results in water imbalances and land degradation in drylands. Management strategies require an in-depth detection of the modes and mechanisms of local land use change. In this study, to detect the process and spatial pattern of land use change and quantify the spatial relations between oasis expansion and the sources of water and human disturbances, enhanced analysis of land transition matrix and location relationship-based spatial analysis were conducted from 1990 to 2015 in the middle reaches of the Heihe River Basin (M-HRB), a typical arid inland river basin in China. The results indicated that cultivated land and desert together accounted for more than 90 % of the study area. In the M-HRB, cultivated land expansion was an obvious process of land use change. Most of the new cultivated land was reclaimed from desert, but the conversion of grassland to cultivated land was the dominant signal of systematic land transition. Swap changes gradually became the main land transition process from 1990 to 2015. The cultivated land showed a close spatial relationship with land and water resources availability, which also constrained the distribution of cultivated land expansion (i.e., within 200-1400 m of human settlements and within 1000 m of water courses or ditches). The quantification results can be used to facilitate smart land management strategies towards sustainable development in the M-HRB. The methods used here can be adapted to other dryland areas for land change detection that supports sustainable land management.

Towards stopping land degradation in drylands: Water‐saving techniques for cultivating biocrusts in situ

AbstractIn recent years, inoculating sand surfaces with biocrust organisms has become one of the most promising biotechnological strategies for controlling and reversing land degradation in drylands. To fully exploit this biotechnology on a large scale in drylands, researchers must explore water‐saving techniques to incubate biocrusts in situ. To achieve this aim, we tested three methods—broadcasting dried cyanobacteria, spraying fresh cyanobacteria, and broadcasting natural biocrust fragments—to culture biocrusts in situ on the Tengger Desert in Northern China. The cover of incubated biocrust increased during the first 2 months after inoculation (from 6% to more than 20.0% in treatments using biocrust fragments); biocrust cover declined but persisted after 12 months of incubation (13.8% cover in the best treatment, natural cyanobacteria fragments). The cover of cyanobacteria was higher than the cover of lichen in our natural cyanobacteria‐lichen crust fragment treatment (NCL; p < .05) after incubating for 12 months. We highlight that cyanobacteria should be selected for biocrust incubation during the initial stages of dryland restoration. Accumulated rainfall was positively related to the cover of incubated biocrust. However, wind speed and wind erosion intensity were both negatively related to the cover of incubated biocrust. In conclusion, broadcasting biocrust fragments is a rapid, efficient, and water‐saving biotechnique to cultivate biocrusts in situ. Actions to reduce wind speed and wind erosion, such as mechanical sand fixing, can help stabilize soils and improve crust cultivation.

Identification and assessment of the factors driving vegetation degradation/regeneration in drylands using synthetic high spatiotemporal remote sensing Data—A case study in Zhenglanqi, Inner Mongolia, China

Abstract Vegetation degradation is a direct distinguishing feature of land degradation in drylands and seriously affects the ecological balance and sustainable development of drylands. Existing assessment methods of vegetation degradation at the regional scale based on long-time-series data have many shortcomings, including coarse resolution and a diversity of vegetation indicators that are typically complex. In the present study, net primary productivity (NPP) was selected as a primary vegetation indicator. Taking Zhenglanqi in the Inner Mongolia Autonomous Region as the study area, a technical process for the assessment of vegetation degradation/regeneration and analysis of the associated driving forces was proposed at a medium–high resolution scale. First, integrating the high spatial resolution advantage of Landsat data and the high temporal resolution advantage of moderate resolution imaging spectroradiometer (MODIS) data, a time series annual NPP dataset from 2001 to 2016 at 30 m resolution was constructed by applying the spatial and temporal adaptive reflectance fusion model (STARFM) and improved Carnegie–Ames–Stanford Approach (CASA) model. Then, the areas of vegetation degradation and regeneration from 2001 to 2016 were identified and determined by annual NPP trend analysis using the Sen + Mann-Kendall method. Overall, vegetation in Zhenglanqi was generally characterized by regeneration, with the degraded and recovered areas being 0.8% and 11.4%, respectively. Nearly 20% of the areas covered by sandy land showed a significant trend of vegetation regeneration, which indicated that the sand-drifting control measures introduced in the Otindag sandy land and its surroundings had achieved significant results. Next, the driving forces of vegetation degradation and regeneration in Zhenglanqi were distinguished over the past 16 years through proposed multiple and partial regression methods. Human activities were the main driver of vegetation degradation and regeneration (68.6% for degradation, 59.9% for regeneration), and the combination of human activities and climate variation also played an important role in vegetation degradation and regeneration (29.3% for degradation, 39.4% for regeneration), which indicated that the significant improvement of vegetation was related to the implemented eco-restoration projects, and visually proved by comparison of high resolution satellite images taking in different years. This research is expected to provide technical support and scientific reference data for ecological protection and land management in the study area, as well as the development of ecological engineering strategies in the drylands of northern China.

Wind erosion and dust from US drylands: a review of causes, consequences, and solutions in a changing world

AbstractErosion by wind is one of the principal processes associated with land degradation in drylands and is a significant concern to land managers and policymakers globally. In the drylands of North America, millions of tons of soil are lost to wind erosion annually. Of the 60 million ha in the United States identified as most vulnerable to wind erosion (arid and dominated by fine sandy soils), 64% are managed by federal agencies (37 million ha). Here we review the drivers and consequences of wind erosion and dust emissions on drylands in the United States, with an emphasis on actionable responses available to policymakers and practitioners. We find that while dryland soils are often relatively stable when intact, disturbances including fire, domestic livestock grazing, and off‐highway vehicles can increase horizontal eolian flux by an order of magnitude, in some cases as much as 40‐fold. A growing body of literature documents the large‐scale impacts of deposited dust changing the albedo of mountain snow cover and in some cases reducing regional water supplies by ~5%. Predicted future increases in aridity and extreme weather events, including drought, will likely increase wind erosion and consequent dust generation. Under a drier and more variable future climate, new and existing soil‐ and vegetation‐disturbing practices may interact in synergistic ways, with dire consequences for environments and society that are unforeseen to many but fairly predictable given current scientific understanding. Conventional restoration and reclamation approaches, which often entail surface disturbance and rely on adequate moisture to prevent erosion, also carry considerable erosion risk especially under drought conditions. Innovative approaches to dryland restoration that minimize surface disturbance may accomplish restoration or reclamation goals while limiting wind erosion risk. Finally, multidisciplinary and multijurisdictional approaches and perspectives are necessary to understand the complex processes driving dust emissions and provide timely, context‐specific information for mitigating the drivers and impacts of wind erosion and dust.

Degradation of Non-Photosynthetic Vegetation in a Semi-Arid Rangeland

Land degradation in drylands is the process in which undesirable conditions emerge due to human and natural causes. Despite the particularly deleterious effects of degradation, and it’s potentially irreversible nature, regional assessments have provided conflicting extents, rates, and severities of degradation, both globally and regionally. Current monitoring of degradation relies upon the detection of green, photosynthetically active parts of vegetation (e.g., leaves). Less is known, however, about the effect of degradation on the non-photosynthetic components of vegetation (e.g., wood, stems, leaf litter) and the relationship between photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and bare soil under degraded conditions (BS). The major objective of the study was to evaluate regional patterns of fractional cover (i.e., PV, NPV, BS) under degraded and non-degraded NPP conditions in a managed rangeland in north Queensland, Australia. Homogenous environmental conditions were identified and each of NPP, PV, NPV, and BS were scaled according to their potential, reference values. We found a strong spatial and temporal correlation between scaled NPP with both scaled PV and scaled BS. Drastic differences were also found for PV and BS between degraded and non-degraded conditions. NPV displayed similarity to both PV and BS, however no clear relationship was found for NPV in all areas, irrespective of degradation conditions.

Land Degradation Assessment Using Residual Trend Analysis of GIMMS NDVI3g, Soil Moisture and Rainfall in Sub-Saharan West Africa from 1982 to 2012

Areas affected by land degradation in Sub-Saharan West Africa between 1982 and 2012 are identified using time-series analysis of vegetation index data derived from satellites. The residual trend (RESTREND) of a Normalized Difference Vegetation Index (NDVI) time-series is defined as the fraction of the difference between the observed NDVI and the NDVI predicted from climate data. It has been widely used to study desertification and other forms of land degradation in drylands. The method works on the assumption that a negative trend of vegetation photosynthetic capacity is an indication of land degradation if it is independent from climate variability. In the past, many scientists depended on rainfall data as the major climatic factor controlling vegetation productivity in drylands when applying the RESTREND method. However, the water that is directly available to vegetation is stored as soil moisture, which is a function of cumulative rainfall, surface runoff, infiltration and evapotranspiration. In this study, the new NDVI third generation (NDVI3g), which was generated by the National Aeronautics and Space Administration-Goddard Space Flight Center Global Inventory Modeling and Mapping Studies (NASA-GSFC GIMMS) group, was used as a satellite-derived proxy of vegetation productivity, together with the soil moisture index product from the Climate Prediction Center (CPC) and rainfall data from the Climate Research Unit (CRU). The results show that the soil moisture/NDVI pixel-wise residual trend indicates land degraded areas more clearly than rainfall/NDVI. The spatial and temporal trends of the RESTREND in the region follow the patterns of drought episodes, reaffirming the difficulties in separating the impacts of drought and land degradation on vegetation photosynthetic capacity. Therefore, future studies of land degradation and desertification in drylands should go beyond using rainfall as a sole predictor of vegetation condition, and include soil moisture index datasets in the analysis.

Degraded land detection by soil particle composition derived from multispectral remote sensing data in the Otindag Sandy Lands of China

Remote sensing technology has shown considerable potential for the estimation of soil properties. In this paper, we proposed a method by using the measured hyperspectral and BJ-1 multispectral image to estimate the silt content in soil quantitatively, and to develop a soil-based model which could be used in detecting desertification or land degradation. The test site was located in the Otindag Sandy Lands in Xilingol League, Inner Mongolia, China. Soil sampling was carried out to analyze the soil particle composition, and the spectral properties of soil samples were also examined in the laboratory. The differences in soil particle composition between the degraded lands and others were distinguished statistically, and the correlation of soil particle contents with spectral reflectance was analyzed based on the Partial Least Squares Regression (PLSR) to determine the sensitive band needed to calibrate the prediction model. The validity of the models was assessed by using the Prediction Residual Error Sum of Squares (PRESS). The results showed that silt content was an important factor to indicate land degradation, and it descended gradually with the development of land degradation. There was significant difference in silt content between degraded lands and the others, the silt content in undegraded lands was nearly three times greater than that in degraded lands. R2 of PLSR model based on the BJ-1 multispectral image (R2=0.504) was lower than that of the measured spectral model (R2=0.725), and validated PRESS (PRESS=0.753) was also higher than that based on the measured spectra (PRESS=0.562). However, the BJ-1 multispectral image did show a considerable ability to predict the soil silt content. Compared with the normal regression method, PLSR was not only effective in dependent or independent variable selection, but it was also reliable to determine the regression model with higher stability and lower error. By combining statistics and manually interactive adjustment, the thresholds of silt contents for categorizing different degraded lands were determined as 3.5% and 8.8%, and it can effectively detect the degraded areas from others; total classification accuracy of this approach reached 86.21%. It verified that the silt content was the best indicator indeed to detect the desertification or land degradation in drylands.

Assessing Land Degradation/Recovery in the African Sahel from Long-Term Earth Observation Based Primary Productivity and Precipitation Relationships

The ‘rain use efficiency’ (RUE) may be defined as the ratio of above-ground net primary productivity (ANPP) to annual precipitation, and it is claimed to be a conservative property of the vegetation cover in drylands, if the vegetation cover is not subject to non-precipitation related land degradation. Consequently, RUE may be regarded as means of normalizing ANPP for the impact of annual precipitation, and as an indicator of non-precipitation related land degradation. Large scale and long term identification and monitoring of land degradation in drylands, such as the Sahel, can only be achieved by use of Earth Observation (EO) data. This paper demonstrates that the use of the standard EO-based proxy for ANPP, summed normalized difference vegetation index (NDVI) (National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) Global Inventory Modeling and Mapping Studies 3rd generation (GIMMS3g)) over the year (ΣNDVI), and the blended EO/rain gauge based data-set for annual precipitation (Climate Prediction Center Merged Analysis of Precipitation, CMAP) results in RUE-estimates which are highly correlated with precipitation, rendering RUE useless as a means of normalizing for the impact of annual precipitation on ANPP. By replacing ΣNDVI by a ‘small NDVI integral’, covering only the rainy season and counting only the increase of NDVI relative to some reference level, this problem is solved. Using this approach, RUE is calculated for the period 1982–2010. The result is that positive RUE-trends dominate in most of the Sahel, indicating that non-precipitation related land degradation is not a widespread phenomenon. Furthermore, it is argued that two preconditions need to be fulfilled in order to obtain meaningful results from the RUE temporal trend analysis: First, there must be a significant positive linear correlation between annual precipitation and the ANPP proxy applied. Second, there must be a near-zero correlation between RUE and annual precipitation. Thirty-seven percent of the pixels in Sahel satisfy these requirements and the paper points to a range of different reasons why this may be the case.

Linking runoff and erosion dynamics to nutrient fluxes in a degrading dryland landscape

Current theories of land degradation assume that shifts in vegetation communities result in changes to the rates and patterns of water and sediment movement, which are vectors of nutrient redistribution. This nutrient redistribution is hypothesized to reinforce, through positive feedbacks, progressive vegetation changes toward a more degraded ecosystem. A key component of this theory, which is currently poorly resolved, is the relative role of runoff and erosion in driving nutrient fluxes from different vegetation types. We address this gap through a series of field‐based, rainfall‐simulation experiments designed to explore plant‐level dynamics of runoff‐ and erosion‐driven nutrient fluxes of N, P and K species. Our results highlight important linkages between physical and biogeochemical processes that are controlled by plant structure. We found that: 1) the magnitude of sediment‐bound nutrient export is determined by the grain‐size distribution of the eroded sediment and the total sediment yield; 2) the partitioning of nutrients in dissolved and sediment‐bound form is determined by the availability and concentration of different nutrient species in the soil or rainfall; 3) these processes varied according to vegetation type and resulted in stark differences between degrading and invading plant communities. Specifically, we observed that grassland areas consistently exported the highest yields of sediment‐bound N, P and K despite producing similar erosion rates to shrub and intershrub areas. Our results have implications for better understanding how grassland areas are being replaced by shrubs and provide insights into the mechanisms of continuing land degradation in drylands.

Perspectives in dryland restoration: approaches for climate change adaptation

Reforestation efforts in dryland ecosystems frequently encounter drought and limited soil productivity, although both factors usually interact synergistically to worsen water stress for outplanted seedlings. Land degradation in drylands (e.g. desertification) usually reduces soil productivity and, especially, soil water availability. In dry sub-humid regions, forest fires constitute a major disturbance affecting ecosystem dynamics and reforestation planning. Climate change projections indicate an increase of drought and more severe fire regime in many dryland regions of the world. In this context, the main target of plantation technology development is to overcome transplant shock and likely adverse periods, and in drylands this is mostly related to water limitations. In this paper, we discuss some selected steps that we consider critical for improving success in outplanting woody plants, both under current and projected climate change conditions including: (1) Plant species selection, (2) Improved nursery techniques, and (3) Improved planting techniques. The number of plant species used in reforestation is increasing rapidly, moving from a reduced set of well-known, easy-to-grow, widely used species, to a large variety of promising native species. Available technologies allow for reintroducing native plants and recovering critical ecosystem functions for many degraded drylands. However, climate change projections introduce large uncertainties about the sustainability of current reforestation practices. To cope with these uncertainties, adaptive restoration approaches are suggested, on the basis of improved plant quality, improved techniques for optimizing rain use efficiency in plantations, and exploring native plant species, including provenances and genotypes, for their resilience to fire and water use efficiency.

Land degradation in drylands: Interactions among hydrologic–aeolian erosion and vegetation dynamics

Land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality. Climate change, shifts in vegetation composition, accelerated soil erosion processes, and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification. Even though the role of hydrologic–aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized, most studies have concentrated only on the role of one or two of these components, and not on the interactions among all three. Drawing on relevant published studies, here we review recent contributions to the study of biotic and abiotic drivers of dryland degradation and we propose a more holistic perspective of the interactions between wind and water erosion processes in dryland systems, how these processes affect vegetation patterns and how vegetation patterns, in turn, affect these processes. Notably, changing climate and land use have resulted in rapid vegetation shifts, which alter the rates and patterns of soil erosion in dryland systems. With the predicted increase in aridity and an increase in the frequency of droughts in drylands around the world, there could be an increasing dominance of abiotic controls of land degradation, in particular hydrologic and aeolian soil erosion processes. Further, changes in climate may alter the relative importance of wind versus water erosion in dryland ecosystems. Therefore acquiring a more holistic perspective of the interactions among hydrologic–aeolian erosion and vegetation dynamic processes is fundamental to quantifying and modeling land degradation processes in drylands in changing climate, disturbance regimes and management scenarios.