| 1. |
- Bargues Tobella, Aida
(författare)
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Assessing soil and land health across two landscapes in eastern Rwanda to inform restoration activities
- 2021
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Ingår i: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 7, s. 767-783
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Tidskriftsartikel (refereegranskat)abstract
- Land degradation negatively impacts water, food, and nutrition security and is leading to increased competition for resources. While landscape restoration has the potential to restore ecosystem function, understanding the drivers of degradation is critical for prioritizing and tracking interventions. We sampled 300–1000 m2 plots using the Land Degradation Surveillance Framework across Nyagatare and Kayonza districts in Rwanda to assess key soil and land health indicators, including soil organic carbon (SOC), erosion prevalence, vegetation structure and infiltration capacity, and their interactions. SOC content decreased with increasing sand content across both sites and sampling depths and was lowest in croplands and grasslands compared to shrublands and woodlands. Stable carbon isotope values (δ13C) ranged from −15.35 ‰ to −21.34 ‰, indicating a wide range of historic and current plant communities with both C3 and C4 photosynthetic pathways. Field-saturated hydraulic conductivity (Kfs) was modeled, with a median of 76 mm h−1 in Kayonza and 62 mm h−1 in Nyagatare, respectively. Topsoil OC had a positive effect on Kfs, whereas pH, sand, and erosion had negative effects. Soil erosion was highest in plots classified as woodland and shrubland. Maps of soil erosion and SOC at 30 m resolution were produced with high accuracy and showed strong variability across the study landscapes. These data demonstrate the importance of assessing multiple biophysical properties in order to assess land degradation, including the spatial patterns of soil and land health indicators across the landscape. By understanding the dynamics of land degradation and interactions between biophysical indicators, we can better prioritize interventions that result in multiple benefits as well as assess the impacts of restoration options.
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| 2. |
- Bargues Tobella, Aida
(författare)
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Determinants of Soil Field-Saturated Hydraulic Conductivity Across Sub-Saharan Africa: Texture and Beyond
- 2024
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Ingår i: Water Resources Research. - 0043-1397 .- 1944-7973. ; 60
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Tidskriftsartikel (refereegranskat)abstract
- Soil infiltration is critical for water security and related ecosystem services. This infiltration, the ability of soils to absorb water at their surface, is controlled by the soil hydraulic conductivity. Despite recent efforts in assembling measurements of soil hydraulic conductivity, global databases and derived pedotransfer functions lack coverage in the tropics. Here, we present soil infiltration measurements and other indicators of soil and land health collected systematically in 3,573 plots from 83 100 km2 sites across 19 countries in sub-Saharan Africa. We use these data to (a) determine field-saturated hydraulic conductivity (Kfs) and (b) explore which variables best predict variation in Kfs. Our results show that sand content, soil organic carbon (SOC), and woody cover had a positive relationship with Kfs, whereas grazing intensity and soil pH had a negative relationship. Our findings highlight that, despite soil texture being important, structure also plays a critical role. These results indicate considerable potential to improve soil hydrological functioning through management and restoration practices that target soil structure. Enhancing SOC content, limiting animal stocking, promoting trees, shrubs, and other vegetation cover, and preventing soil erosion can increase Kfs and improve water security. This data set can contribute to improving Earth system and land surface models for applications in Africa.We present field infiltration measurements and accompanying indicators of soil and land health from 3,573 plots across sub-Saharan Africa Field-saturated hydraulic conductivity (Kfs) is associated with soil texture and factors related to soil structure Our results suggest that soil hydrological functioning can be enhanced through management practices that target soil structure
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| 3. |
- Bargues Tobella, Aida
(författare)
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Determination of land restoration potentials in the semi-arid areas of Chad using systematic monitoring and mapping techniques
- 2023
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Ingår i: Agroforestry Systems. - : Springer Science and Business Media LLC. - 0167-4366 .- 1572-9680. ; 97, s. 1289-1305
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Tidskriftsartikel (refereegranskat)abstract
- The restoration of degraded lands has received increased attention in recent years and many commitments have been made as part of global and regional restoration initiatives. Well-informed policy decisions that support land restoration, require spatially explicit information on restoration potentials to guide the design and implementation of restoration interventions in the context of limited resources. This study assessed ecosystems indicators of land degradation using a systematic approach that combines field surveys and remote sensing data into a set of multi-criteria analyses to map restoration potentials in the semi-arid areas. The indicators considered were soil organic carbon, erosion prevalence, enhanced vegetation index, Normalized differences water index and the Net Primary productivity. Three classes of restoration potential were established: (1) areas not in need of immediate restoration due low degradation status, (2) areas with high potential for restoration with moderate efforts required and (3) areas in critical need of restoration and require high level of efforts. Of the total area of the study site estimated at 88,344 km2, 59,146.12 km2, or 66.94% of the theoretically recoverable area, was considered suitable for restoration, of which 38% required moderate efforts while 28% require less efforts. The recoverable areas suitable for restoration could be restored through tree planting, soil and water conservation practices, farmers managed natural regeneration, and integrated soil fertility management. These results can help to spatially identify suitable multifunctional restoration and regeneration hotspots as an efficient way to prioritize restoration interventions in the context of limited resources.
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| 4. |
- Bargues Tobella, Aida, et al.
(författare)
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Explore before you restore: Incorporating complex systems thinking in ecosystem restoration
- 2024
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Ingår i: Journal of Applied Ecology. - 0021-8901 .- 1365-2664. ; 61, s. 922-939
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Forskningsöversikt (refereegranskat)abstract
- The global movement for ecosystem restoration has gained momentum in response to the Bonn Challenge (2010) and the UN Decade on Ecosystem Restoration (UNDER, 2021–2030). While several science-based guidelines exist to aid in achieving successful restoration outcomes, significant variation remains in the outcomes of restoration projects. Some of this disparity can be attributed to unexpected responses of ecosystem components to planned interventions.Given the complex nature of ecosystems, we propose that concepts from Complex Systems Science (CSS) that are linked to non-linearity, such as regime shifts, ecological resilience and ecological feedbacks, should be employed to help explain this variation in restoration outcomes from an ecological perspective.Our framework, Explore Before You Restore, illustrates how these concepts impact restoration outcomes by influencing degradation and recovery trajectories. Additionally, we propose incorporating CSS concepts into the typical restoration project cycle through a CSS assessment phase and suggest that the need for such assessment is explicitly included in the guidelines to improve restoration outcomes.To facilitate this inclusion and make it workable by practitioners, we describe indicators and methods available for restoration teams to answer key questions that should make up such CSS assessment. In doing so, we identify key outstanding science and policy tasks that are needed to further operationalize CSS assessment in restoration.Synthesis and applications. By illustrating how key Complex Systems Science (CSS) concepts linked to non-linear threshold behaviour can impact restoration outcomes through influencing recovery trajectories, our framework Explore Before You Restore demonstrates the need to incorporate Complex Systems thinking in ecosystem restoration. We argue that inclusion of CSS assessment into restoration project cycles, and more broadly, into international restoration guidelines, may significantly improve restoration outcomes.
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| 5. |
- Bargues Tobella, Aida, et al.
(författare)
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Forest restoration: Transformative trees
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 366, s. 316-317
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Tidskriftsartikel (refereegranskat)
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| 6. |
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| 7. |
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| 8. |
- Bargues Tobella, Aida, et al.
(författare)
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Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa
- 2017
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Ingår i: Ecohydrology. - : Wiley. - 1936-0584 .- 1936-0592. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Agroforestry parklands, in which annual crops are grown under scattered mature trees, constitute the most prevalent farming system in semiarid West Africa, covering vast areas of land. The most dominant tree species in these systems is Vitellaria paradoxa, an indigenous tree to West Africa. Despite the importance of this tree in the region, no study to our knowledge has examined its sources and patterns of water uptake. In this study, we used oxygen stable isotopes at natural abundance levels to investigate water sources used by V. paradoxa both in the dry and wet season in an agroforestry parkland in Burkina Faso. We found that during the wet season soil moisture was highest near the soil surface (< 10 cm depth), yet during this time V. paradoxa preferentially accessed water from slightly deeper soil depths, obtaining ca. 90% of its water from 10 to 50 cm depth. In contrast, soil moisture in the upper soil layers was significantly lower during the dry season and as a result V. paradoxa shifted to deeper water sources, obtaining ca. 30% of its water from groundwater and ca. 50% from 30 to 600 cm depth. We also found a negative relationship between tree size and the contribution of groundwater during the dry season, whereas during the wet season V. paradoxa predominantly used water near the soil surface regardless of tree size. Knowledge about the sources and patterns of tree water uptake provides crucial information to better understand how trees influence the local water balance.
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| 9. |
- Bargues Tobella, Aida, et al.
(författare)
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The effect of trees on preferential flow and soil infiltrability in an agroforestry parkland in semiarid Burkina Faso
- 2014
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Ingår i: Water Resources Research. - 0043-1397 .- 1944-7973. ; 50, s. 3342-3354
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Tidskriftsartikel (refereegranskat)abstract
- Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planting in these environments is generally discouraged due to the large water consumption by trees, but this view may neglect their potential positive impacts on water availability. The effect of trees on soil hydraulic properties linked to groundwater recharge is poorly understood. In this study, we performed 18 rainfall simulations and tracer experiments in an agroforestry parkland in Burkina Faso to investigate the effect of trees and associated termite mounds on soil infiltrability and preferential flow. The sampling points were distributed in transects each consisting of three positions: (i) under a single tree, (ii) in the middle of an open area, and (iii) under a tree associated with a termite mound. The degree of preferential flow was quantified through parameters based on the dye infiltration patterns, which were analyzed using image analysis of photographs. Our results show that the degree of preferential flow was highest under trees associated with termite mounds, intermediate under single trees, and minimal in the open areas. Tree density also had an influence on the degree of preferential flow, with small open areas having more preferential flow than large ones. Soil infiltrability was higher under single trees than in the open areas or under trees associated with a termite mound. The findings from this study demonstrate that trees have a positive impact on soil hydraulic properties influencing groundwater recharge, and thus such effects must be considered when evaluating the impact of trees on water resources in drylands.
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| 10. |
- Bargues Tobella, Aida
(författare)
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The importance of tree cover for water resources in semiarid West Africa
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current paradigm in forest hydrology implies that an increase in tree cover always leads to reduced water yields as a result of increased interception and transpiration (ET) losses. This trade-off theory, in which more trees mean less water, has led to concerns that the establishment of trees in drylands may jeopardize scarce water resources. But in the seasonally dry tropics relevant studies are scarce, and few have explored the impact of intermediate tree densities on water yields in degraded soils, which greatly limits the applicability of the trade-off theory in this region. Here, I propose an alternative optimum tree cover theory in which, under conditions typical of the seasonally dry tropics, groundwater recharge is maximized at an intermediate tree cover. At tree covers below this optimum, the gains from more trees on soil hydraulic properties exceed their additional ET losses, leading to increased groundwater recharge. The overall aim of this thesis is to test this hypothesis and to clarify the main processes influencing the relationship between tree cover and groundwater recharge. To do this, a number of measurements were taken in an agroforestry parkland in semiarid West Africa; these included soil infiltrability, soil water drainage, tree transpiration and degree of preferential flow, in combination with stable isotope data. Results from this thesis show that deep soil water drainage was minimal near the tree stem, reached a maximum close to the canopy edge and from there decreased linearly with increasing distance to the nearest tree. This pattern is probably the result of a combination of increased ET losses next to the tree and reduced infiltrability and preferential flow with increasing distance from the nearest tree. The combined increase in infiltrability and degree of preferential flow close to trees allows for enhanced soil and groundwater recharge. Tree transpiration data were used in combination with the observed pattern in soil water drainage and data on tree water sources to model groundwater recharge as a function of tree cover. Modelling results confirm that groundwater recharge was maximized under intermediate tree cover irrespective of the scenarios considered. That trees do not always reduce water yields but can substantially improve them suggests new opportunities for tree protection and tree-based restoration in the seasonally dry tropics, benefitting hundreds of millions of people.
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