Seasonal and interannual dynamics in dwarf rush vegetation in the Southwestern Iberian Peninsula
In the western Mediterranean climate zone, vegetation dynamics lead to a seasonal change from Isoeto-Nanojuncetea communities to Helianthemetea communities. The interannual as well as the intra-annual pattern of this vegetation type was investigated using a permanent plot approach. In two regions with similar climatic conditions, the Serra de Monchique (Algarve, Portugal) and the Campo de Gibraltar (Andalusia, Spain), dwarf rush communities were sampled at five different altitudinal levels (50 m a.s.l. to 710 m a.s.l.). Frequency data were recorded for 74 permanent plots of 0.25 m2. Both study sites were analysed separately applying correspondence analysis. Poisson regression models were estimated on a species level to discern trends from fluctuation. The development of species diversity was observed concomitantly.The transition from the autumnal phase which is dominated by geophytes to the spring and summer phases follows approximately the same pattern in both study regions. With the exception of the well discernible autumnal ecophase there is a smooth transition from the predominance of species characteristic of Isoeto-Nanojuncetea communities to the predominance of Helianthemetea species. During this transition, the diversity of the sites is stable. A decline towards the end of the observation period is provoked by the beginning summer drought. Water and energy supply are important factors responsible for the described pattern.The interannual fluctuations equal or surpass the seasonal fluctuation in view of the apparent vegetation. This pattern is supposed to be induced by the strong influence of the spatial and temporal distribution of rainfall on the germination of annuals.