Abstract
Mountain ecosystems are vulnerable because of land-use and climate change. In this study, we performed a re-visitation study using historical and newly collected vegetation plots to explore the primary trends in the floristic, ecological, and structural features of Mediterranean Pinus mugo krummholz over past decades. The plant community composition over time (1992 vs. 2016–17) was analyzed by a detrended correspondence analysis followed by a statistical comparison of time steps and an analysis of the contribution of each species to temporal differences. Ecological and structural changes were analyzed by a permutational multivariate analysis of variance followed by a post hoc comparison. We observed relevant changes in the floristic composition, structure, and ecological characteristics of Pinus mugo scrub. Some subalpine and treeline species that characterize the early stages of Pinus mugo succession declined as several warm-adapted species increased. Furthermore, these changes were most likely due to the natural evolution of high-mountain krummholz combined with a thermophilization process occurring in alpine habitats. In contrast, a small group of cold-adapted species also increased, probably because the patchy spatial pattern of Pinus mugo scrubs gives rise to “mesic patches” in a matrix of arid grasslands. The re-visitation approach adopted for long-term analysis in this study can potentially be applied to other mountainous regions to better understand long-term ecological changes in high alpine vegetation.
Highlights
High mountain habitats are vulnerable because of human impacts, such as global change and land abandonment, which influence biodiversity and ecosystem functioning [1,2,3,4]
These changes have been related to the abandonment of traditional grazing and agroforestry activities that began after the 1950s [2,28], as well as global warming [32,33]
As observed in the Alps [27,76], such changes should be related to a recent increase in Pinus mugo thicket cover, which occurred following the abandonment of traditional grazing activities in combination with global warming processes
Summary
High mountain habitats are vulnerable because of human impacts, such as global change (e.g., rising temperatures, changes in precipitation patterns, and nitrogen deposition) and land abandonment, which influence biodiversity and ecosystem functioning [1,2,3,4]. Regarding Pinus mugo scrubs, a widespread expansion has been recorded across European mountains since the 1950s, mainly at the expense of secondary grasslands, whose extent have been reduced [25,26,27,28,29,30,31]. These changes have been related to the abandonment of traditional grazing and agroforestry activities that began after the 1950s [2,28], as well as global warming [32,33]. Dullinger et al [27] and Wild et al [34] showed that despite the favorable climatic conditions of European subalpine regions, Pinus mugo colonizes high-mountain abandoned pastures at low rates
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