After sigmatism: What we learned on spatiotemporal changes in grassland communities after 10 years
Data de publicació1998
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In this paper we summarize our findings on grassland communities after more than ten years of research on spatiotemporal patterns of vegetation, phenology, productivity and species richness. Grassland species from the Pyrenees and Cantabric mountains are organized in guild, and coexistence was facilitated through vegetation stratification and temporal shifts in phenology between plant guilds. Graminoids were the most abundant group, developed earlier and grew taller than forbs. Most of the forms were rare plants and acted as fugitives. Some of the were relatively abundant either in the seed rain or in the soil seed bank, although in general reproduction by seeds was scarce. Feedback processes and spatiotemporal changes of resources at different scales, including fertility and available space by gap opening, interacted to produce community structure in subalpine grasslands. At the landscape scale, fertility was the main factor structuring grasslands communities, and although it varied gradually, two separated mesic and xeric community types resulted, as defined by plant species composition. Grazing was the main biotic disturbance and acted at several scales, increasing the space available for establishment and producing changes in composition. In montane grasslands there were changes in nitrogen fluxes in vole and mole mounds, resulting in an increase of funerals, annuals an non-mycorrhizal plants, such as Caryophyllaccae. Only in subalpine ant hills, among the bionically formed mounds, was possible to find species not present in the surrounding pasture, such as Fistula gautieri and Vicia Pyrenaica, usually found awn unstable slopes. In conclusion, community organization is an extremely complex process, resulting from the action of different feedbacks and stochastic mechanism operating at different spatial and temporal scales, and no simple mechanism explains the process.