<p>Soil is a key element in the Earth system, and changes in land management can affect soil organic carbon (SOC) dynamics and the provision of ecosystem services related to soil. The content and stock of SOC has been adopted as the measure to be used for land degradation assessment. Nevertheless, SOC dynamics linked to land use and land cover changes after land abandonment is still a controversial issue. From the mid-20<sup>th</sup> century, Mediterranean mountains have undergone intense transformations due to climate change and severe socio-economic marginalisation, linked to depopulation and cropland and pasture abandonment. These processes led to a very different landscape, with a massive invasion of shrubs, secondary succession to forest and afforested areas. The objective of this study is to analyse the effects of post-land abandonment management practices on soil organic carbon dynamics (stocks and fractions). We selected three land abandonment scenarios in the Central Pyrenees: (i) natural revegetation with broadleaf vegetation; (ii) natural revegetation versus afforestation with coniferous forest; and (iii) abandonment of grasslands and woody encroachment. The total SOC stocks and fractions (through density fractionation) were analysed: Free light Fraction (FLF), Occluded Light Fraction (OLF), and Heavy Fraction (HF). Results showed that: (i) revegetation resulted in a constant and slow SOC accumulation processes; (ii) grassland enhanced accumulation of SOC, and the woody encroachment of these areas produced a significant loss of SOC during the first revegetation stages; (iii) density fractions were significantly affected by land use and land cover changes; (iv) the labile fractions (FLF and OLF) were significantly higher under coniferous forest than under grassland and shrubland; and (v) differences were also observed between coniferous and broadleaf forest, suggesting that broadleaf litter is incorporated faster in the mineral soil. The present study showed that land abandonment in Mediterranean mountains does not only affect SOC stocks, but also triggers the addition of labile carbon into the soil. It also changes the dynamics and sequestration of stable SOC, making this information essential in the design of future post-land abandonment strategies.</p><p>&#160;</p><p>Acknowledgements: This research project was supported by the MANMOUNT (PID2019-105983RB-100/AEI/ 10.13039/501100011033) project funded by the MICINN-FEDER and the PRX21/00375 project funded by the Ministry of Universities of Spain from the &#8220;Salvador de Madariaga&#8221; programme. Melani Cortijos-L&#243;pez is working with an FPI contract (PRE2020-094509) from the Spanish Ministry of Economy and Competitiveness associated to the MANMOUNT project. Manel Llena has a &#8220;Juan de la Cierva Formaci&#243;n&#8221; postdoctoral contract (FJC2020-043890-I/AEI/ 10.13039/501100011033) from the Spanish Ministry of Science and Innovation.</p>
<p>Water resources availability is one of the main concerns for policy makers around the World. In the Mediterranean basin, this problem has been increased given the extreme variability in climate and the land use changes that have occurred during the last century (i.e. land abandonment). Streamflow and other environmental variables related to vegetation have been analysed in three Mediterranean mid-mountain basins under conditions of Climate Change (CC), under conditions of Land Use Change (LUC) and under its Combined Action (CA). The Land Use changes have been defined in the framework of the Life MIDMACC project and are related to land management through shrubland cleaning activities in abandoned fields and forest management that is determined by a 50% decrease in tree density in a forest community.</p><p>Three basins (Leza, Estarr&#250;n and L'Anyet) have been simulated using the Regional Hydro-Ecologic Simulation System (RHESSys) for the periods 2035-2064 and 2070-2099. The aim of the study is to determine the impacts of climate change and land management on both streamflow and other variables such as Net Primary Production or Potential Evapotranspiration in these basins (representative of Mediterranean mid-mountains) in order to analyse how the management proposed can be used to adapt these basins to climate and whether it is capable of mitigating the forecast reduction in streamflow associated with climate trends.</p><p>The results with LUC reveal a clear positive trend, increasing the streamflow in the basins of Leza and L'Anyet rivers (+9.76% and +4.70%) and slightly decrease (-0.13%) in Estarr&#250;n river due to the limited area to be managed. The combined action (CA) shows, in general, an attenuation in the clear negative trend of streamflow under climate change (CC) conditions. This suggests that the land management proposed in the LIFE MIDMACC project could help the adaptation of Mediterranean mid-mountain basins to climate change and the mitigation of its effects.</p><p>Acknowledgements: This research project was supported by the Life MIDMACC project ((LIFE18 CCA/ES/001099)) project funded by the European Commission. Melani Cortijos-L&#243;pez is working with an FPI contract (PRE2020-094509) from the Spanish Ministry of Economy and Competitiveness associated to the MANMOUNT project. Manel Llena has a &#8220;Juan de la Cierva Formaci&#243;n&#8221; postdoctoral contract (FJC2020-043890-I/AEI/ 10.13039/501100011033) from the Spanish Ministry of Science and Innovation.</p><p>&#160;</p><p>&#160;</p>
<p><span>During the second half of the 20</span><sup><span>th</span></sup><span> century the mountain areas of the Mediterranean region undergone an intense process of rural abandonment. This process together with a transition to warmer and drier climatic conditions caused a decrease in runoff and sediment yield, which have several consequences from hydrological, geomorphological and ecological points of view. L</span><span>and use management of these areas has become a target of environmental authorities and stakeholders to ensure the sustainability of ecosystem services</span><span>. An active management has been applied in some areas through the reduction of vegetation density or by human afforestation, while other areas have not been managed, undergoing a natural process of revegetation. In this context, assessing the contribution of different land use management on runoff is fundamental for addressing water management at the catchment and regional scales, especially in a context of climate change. The main objective of this work is to analyse the relative effects of land use management techniques to hydrological connectivity and water yield in a Mediterranean mid-mountain basin. To pursue this objective, we applied hydrological connectivity (IC index) and ecohydrological (RHESSys) models to different sub-catchments of the Leza Valley (Iberian System, Spain), representative of three different scenarios: (i) natural revegetation, (ii) human afforestation, and (iii) shrub clearing. Results show how hydrological connectivity tends to decrease when vegetation cover increases (i.e., natural revegetation and human afforestation) while tends to increase when shrub clearing takes place. Runoff coefficient followed a similar pattern, decreasing in basins where vegetation increases and decreasing where there is vegetation clearing. Important differences were observed in terms of the distribution of connectivity changes, their location in relation to the outlet and the effects on surface runoff.</span></p><p><span>This research project was supported by the MANMOUNT (PID2019-105983RB-100/AEI/ 10.13039/501100011033) project funded by the MICINN-FEDER and the PRX21/00375 project funded by the Ministry of Universities of Spain from the &#8220;Salvador de Madariaga&#8221; programme. Manel Llena has a &#8220;Juan de la Cierva Formaci&#243;n&#8221; postdoctoral contract (FJC2020-043890-I/AEI/ 10.13039/501100011033) from the Spanish Ministry of Science and Innovation, while Melani Cortijos-L&#243;pez is working with an FPI contract (PRE2020-094509) from the Spanish Ministry of Economy and Competitiveness associated to the MANMOUNT project. </span></p><p align="justify">&#160;</p>
<p>Mid-mountain catchments across the Mediterranean basin undergone a decrease in runoff and sediment yield during the second half of the 20<sup>th</sup> century mainly due to forest cover increase following rural abandonment together with a transition to drier climatic conditions. In the same way, due to the revegetation and afforestation processes these zones experienced the homogenization of the ancient cultural landscapes, which have several consequences from ecological, geomorphological and hydrological points of view. During last decades, land use management of these areas have become a target of environmental policy makers and stakeholders to ensure the sustainability of ecosystem services. In some areas have been applied an active management through the reduction of vegetation density or by human afforestation, while others undergone a natural process of revegetation. In these setting, the conservation status of agricultural terraces plays a key role on the overall catchment response in terms of overland flow and sediment transport due to its potential effects on water and sediment connectivity between the hillslopes and the main channels. In this context, assessing the contribution of different land use management on runoff is fundamental for addressing water management and soil loss at the catchment and regional scales, especially in a context of climate change. Within this background, the aim of this work is to analyse the relative effects of terracing and land use management techniques to hydrological connectivity and water yield in a Mediterranean mid-mountain basin. To pursue this objective, we applied hydrological connectivity (IC index) and ecohydrological (RHESSys) models to different sub-catchments of the Leza Valley (Iberian System, Spain), representative of five different landscapes: (i) natural revegetation; (ii) natural revegetation with terracing reconstruction; (iii) human afforestation; (iv) human afforestation with terracing reconstruction; and (v) shrub clearing.</p><p>This research is part of the MANMOUNT project (PID2019-105983RB-100/AEI/ 10.13039/501100011033) funded by the MICINN.</p>
<p>Mediterranean mountains have been affected by an intense process of cropland abandonment since the middle of the last century, as a result of the rural exodus. This has led to the activation of natural revegetation processes in marginal areas that have not been managed. Literature has recorded different soil responses to secondary succession depending on factors such as climate, altitude, soil depth and type, but still very little is known about the influence of soil pH. Thus, the main objective of this work is to identify how soil quality and carbon sequestration are affected by secondary succession after abandonment for two types of soil lithologies (acidic and alkaline). For this purpose, the Leza Valley (La Rioja, Spain) was selected as the representative study area. Soil samples were collected for each lithology, at different depths (0-40 cm), for 5 stages of succession (cropland (CRL); shrubland (SH); bushland (BS); young forest (YF); and old forest (OF)), and their physicochemical properties were analysed in the laboratory. Data analysis was carried out and these are the most relevant results: i) there are significant differences between acidic and alkaline organic carbon stocks; ii) the alkaline soils increase their SOC stock with the advance of succession, and significant differences were observed between the first stages of abandonment and BS, YF and OF; iii) while in the acidic soils no significant differences were observed, and the highest values were recorded in YF; iv) these results may be the combination of interactions between pH, soil properties and plant and microbiological communities that establish in these areas. Our work has shown the relevance of considering the lithology of our soils in order to determine which post-abandonment management practices may be the most appropriate for our study area. Therefore, it is necessary that policies and management strategies include this type of analysis to achieve the best results of soil carbon sequestration.</p> <p>Acknowledgement: This research project was supported by the MANMOUNT (PID2019-105983RB-100/AEI/ 10.13039/501100011033) project funded by the MICINN-FEDER. Melani Cortijos-L&#243;pez is working with an FPI contract (PRE2020-094509) from the Spanish Ministry of Economy and Competitiveness associated to the MANMOUNT project</p> <p>Keywords: abandoned croplands, natural revegetation, carbon sequestration, soil pH, Iberian System (Spain)</p>
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