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Uso e gestão do solo na Margem Esquerda do Guadiana: trajectórias de transformação e serviços de ecossistema num clima em mudança
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Nas paisagens semiáridas do Baixo Alentejo interior, as dinâmicas de uso e gestão do solo apresentam forte heterogeneidade, resultante da relação entre a evolução histórica da ocupação agrícola e os recursos naturais disponíveis, em particular o solo e a água. Na Margem Esquerda do Guadiana coexistem trajectórias contrastantes: nos solos férteis persistem os cereais de sequeiro; nas áreas beneficiárias do regadio do Alqueva instalaram-se sistemas super-intensivos de culturas permanentes, como o olival; e nos solos pobres e declivosos, com propriedade fragmentada, verifica-se uma trajectória dual, onde o regime extensivo do Montado coexiste com o abandono agrícola e a renaturalização espontânea. A cessação da actividade agrícola implica perda de valor económico directo, mas promove a recuperação ecológica e a produção de serviços de ecossistema, incluindo o suporte à biodiversidade e a regulação climática através do sequestro de carbono. A análise dos processos de reorganização ecológica após o abandono é, por isso, essencial para compreender o potencial de regeneração, o ritmo da recuperação e os limiares que a condicionam. Os talhões do Centro Experimental de Erosão de Vale Formoso (CEEVF), na Serra de Serpa e Mértola, constituem um laboratório para o estudo da degradação e regeneração sob condições controladas. Foram analisadas trajectórias de recuperação com base na evolução da vegetação e da camada superficial do solo após o abandono em diferentes momentos, pontos de partida e graus de degradação prévia. Os resultados mostram uma transição de sistemas dominados por processos físicos de erosão para sistemas regulados biologicamente, com aumento do coberto vegetal e acumulação de carbono no solo até à estabilização a partir da fase arbustiva. Estes resultados suportam um modelo conceptual de trajectórias de recuperação com histerese ecológica, onde a intensidade e a duração do uso agrícola condicionam o ritmo e a amplitude da regeneração. A compreensão destes mecanismos de regeneração espontânea é fundamental para orientar estratégias de planeamento territorial e gestão dos recursos naturais com vista à mitigação e adaptação à mudança climática.
In the semi-arid landscapes of the Southeastern Alentejo, land use and management dynamics are highly heterogeneous, shaped by the interaction between the historical evolution of land use and the availability of natural resources, particularly soil and water. On the left bank of the Guadiana River, there are contrasting trajectories: on fertile soils, rainfed cereals persist; in areas benefiting from Alqueva irrigation, super-intensive permanent crops such as olive groves have been established; and on poor, degraded lands with fragmented ownership, a dual trajectory emerges, where the extensive Montado regime coexists with agricultural abandonment and spontaneous rewilding. The cessation of agricultural activity results in a loss of direct economic value but promotes ecological recovery and ecosystem services, including biodiversity support and climate regulation through carbon sequestration. Analysing ecological processes following land abandonment is therefore essential to understanding the potential for regeneration, the pace of recovery, and associated thresholds. Plots at the Vale Formoso Soil Erosion Experimental Centre (CEEVF) serve as a natural laboratory for studying land degradation and ecosystem recovery under controlled conditions. Recovery trajectories were analysed based on the evolution of vegetation cover and structure, as well as soil surface processes after abandonment, across different periods, initial conditions, and degrees of previous degradation. The results reveal a transition from systems dominated by physical processes to biologically regulated systems, characterized by increased vegetation cover and soil carbon accumulation until apparent stabilization after shrub establishment. These findings support a conceptual model of recovery trajectories with ecological hysteresis, in which the intensity and duration of agricultural use determine both the pace and extent of recovery. Understanding these spontaneous mechanisms is fundamental for informing land-use planning and natural resource management strategies aimed at climate change mitigation and adaptation.
In the semi-arid landscapes of the Southeastern Alentejo, land use and management dynamics are highly heterogeneous, shaped by the interaction between the historical evolution of land use and the availability of natural resources, particularly soil and water. On the left bank of the Guadiana River, there are contrasting trajectories: on fertile soils, rainfed cereals persist; in areas benefiting from Alqueva irrigation, super-intensive permanent crops such as olive groves have been established; and on poor, degraded lands with fragmented ownership, a dual trajectory emerges, where the extensive Montado regime coexists with agricultural abandonment and spontaneous rewilding. The cessation of agricultural activity results in a loss of direct economic value but promotes ecological recovery and ecosystem services, including biodiversity support and climate regulation through carbon sequestration. Analysing ecological processes following land abandonment is therefore essential to understanding the potential for regeneration, the pace of recovery, and associated thresholds. Plots at the Vale Formoso Soil Erosion Experimental Centre (CEEVF) serve as a natural laboratory for studying land degradation and ecosystem recovery under controlled conditions. Recovery trajectories were analysed based on the evolution of vegetation cover and structure, as well as soil surface processes after abandonment, across different periods, initial conditions, and degrees of previous degradation. The results reveal a transition from systems dominated by physical processes to biologically regulated systems, characterized by increased vegetation cover and soil carbon accumulation until apparent stabilization after shrub establishment. These findings support a conceptual model of recovery trajectories with ecological hysteresis, in which the intensity and duration of agricultural use determine both the pace and extent of recovery. Understanding these spontaneous mechanisms is fundamental for informing land-use planning and natural resource management strategies aimed at climate change mitigation and adaptation.
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Sequestro de carbono Abandono agrícola Sucessão ecológica Planeamento territorial Carbon Sequestration Agricultural Land Abandonment Ecological Succession Territorial Planning