Alpine vegetation dynamics and conservation. The pyrenean mires

Resumen

Multiple processes determine the structure and diversity of plant communities. The study of these processes, or community assembly, is a central part of the study of terrestrial ecology in the recent decades.In the Alpine mountains mires occupy inland insular habitats, which face natural fragmentation and environmental conditions variation both within a mire and between distant mires. In addition, mire communities are exposed toland use changes and climate change. In this thesis, we want to understand how these communities respond to changes in differentecological and land use factors. The results shown and discussed should enableto assess the conservation status of the alpine mires, to revealwhat their current threats are,and to perform science-basedmanagement decisions. Here, we studied the vegetation dynamics of mires from the Central Pyrenees at different temporal and spatial scales. More concretely, we studied the relationshipbetweenwater table depthandplant-plant interactionsof three engineering plant species; we assessed the responses of the vegetationunder contrasting grazing conditionsina three years experiment; we studied which bioclimatic and land use factors facilitate the mires encroachmentby Pinus uncinata; and we studied beta diversity patterns among mire communities ata regional scale. At shoot or plant level, growth performance proved to be the basis of the competitive abilities of the three species studied, independentlyofthewater level. Lateral expansion of clonal plants was the mainmechanism in gap colonizationafter grazing exclusion, whereassexual reproduction hada secondary role in vegetation dynamicsat short scales. The current spontaneous reforestation of the subalpine belt resonates even in the mire systems, where pine encroachment has increased at places, namely at the neighborhood of pinewoods. At regional scale, beta diversitypatternsshowedthat each mire siteharborsits floristic singularity, whereasenvironmental gradients are lessrelevant in the community assembly of these inland insular habitats. Overall, the vegetation dynamics in Alpine mires proceeds very slowlyat wide geographical scales, but remarkable changes in plant developmentoccurin short timeat detailed scales.