The effects of long-term fertilization on the temporal stability of alpine meadow communities

Abstract

Recent theoretical and experimental work suggests that species diversity enhances the temporal stability of communities. However, empirical support largely comes from experimental communities. The relationship between diversity and stability in natural communities, and the ones facing environmental changes in particular, has received less attention. We created a gradient of fertility in a natural alpine meadow community to test the effects of diversity and fertilization on the temporal variability of community cover and cover of component species and to determine the importance of asynchrony, portfolio effects, cover and dominance for diversity-stability relationships. Although fertilization strongly reduced species richness, the temporal stability in community cover increased with fertilization. Most species showed a decline of temporal stability in mean population cover with fertilization, but two grass species, which dominated fertilized communities after 10 years, showed an increase of stability. Detailed analysis revealed that the increased dominance of these two highly stable grass species was associated with increased community stability at high levels of fertilization. In contrast, we found little support for other mechanisms that have been proposed to contribute to community stability, such as changes in asynchrony and portfolio effects. We conclude that the presence of highly productive species that have stabilizing properties dominate fertilized assemblages and enhance ecosystem stability.