Abstract
Over the last decades, global changes have altered the structure and properties of natural and semi-natural mountain grasslands. Those changes have contributed to grassland loss mainly through colonization by woody species at low elevations, and increases in biomass and greenness at high elevations. Nevertheless, the interactions between agropastoral components; i.e., ecological (grassland, environmental, and geolocation properties), social, and economic components, and their effects on the grasslands are still poorly understood. We estimated the vulnerability of dense grasslands in the Central Pyrenees, Spain, based on the connectivity loss (CL) among grassland patches that has occurred between the 1980s and the 2000s, as a result of i) an increase in biomass and greenness (CL-IBG), ii) woody encroachment (CL-WE), or iii) a decrease in biomass and greenness (CL-DBG). The environmental and grassland components of the agropastoral system were associated with the three processes, especially CL-IBG and CL-WE, in relation with the succession of vegetation toward climax communities, fostered by land abandonment and exacerbated by climate warming. CL-IBG occurred in pasture units that had a high proportion of dense grasslands and low current livestock pressure. CL-WE was most strongly associated with pasture units that had a high proportion of woody habitat and a large reduction in sheep and goat pressure between the 1930s and the 2000s. The economic component was correlated with the CL-WE and the CL-DBG; specifically, expensive pastures were the most productive and could maintain the highest rates of livestock grazing, which slowed down woody encroachment, but caused grassland degradation and DBG. In addition, CL-DBG was associated with geolocation of grasslands, mainly because livestock tend to graze closer to passable roads and buildings, where they cause grassland degradation. To properly manage the grasslands, an integrated management plan must be developed that includes an understanding of all components of the agropastoral system and takes into account all changes that have occurred in dense mountain grasslands. Addressing the problems individually risks the improvement of some grasslands and the deterioration of others.
Highlights
Semi-natural mountain grasslands are protected by the EU Habitats Directive and require management, especially through grazing, for their maintenance [1]
The Goodness of Fit (GoF) index indicated that the overall fit of the models in explaining those relationships was high (GoFCL-in biomass and greenness (IBG) = 0.8, GoFCL-WE = 0.9, and GoFCL-decreases in biomass and greenness (DBG) = 0.7)
In dense grasslands of the Central Pyrenees, Spain, we identified the components of the agropastoral system that were correlated with connectivity loss (CL) caused by increases in biomass and greenness (IBG), woody encroachment (WE), and decreases in biomass and greenness (DBG)
Summary
Semi-natural mountain grasslands are protected by the EU Habitats Directive and require management, especially through grazing, for their maintenance [1]. The environmental factors and management practices that allowed the creation of those grasslands have changed [2, 3]. If those habitats are misused or mismanaged, they will disappear, either through succession toward the climax vegetation [4,5,6] or through degradation [7]. Once a resilience threshold has been exceeded, the grassland structure changes [11,12,13], through increases in woody encroachment, changes in biomass and greenness [8, 14, 15], or connectivity loss among vegetation communities [5, 16]. Persistence of traditional land uses is vital for the preservation of those grasslands [17]
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