2008). Furthermore, current riparian clear cut practices, such as those present in the study area, have been identified as a cause of decreasing riparian species richness in the Iberian Peninsula (Salinas et al. 2000). Higher total plant richness was recorded when more of the sclerophyllous species were present. This is not unexpected as riparian plant richness is unique (Sabo et al. 2005), and thus contribution from upland plants can only result in an increase in local richness. BACE inhibitor On average 48% of the total plant richness was due to the presence of strictly riparian plants, which was almost twice the average contribution
of the sclerophyllous plants (28%). This indicates that the riparian community is mainly dominated by strictly riparian plants. Since strictly riparian plants occur in limited numbers (Pollock et al. 1998; Sabo et al. 2005) the maximum richness is truncated, and increases are only possible with the addition of sclerophyllous species. In fact, higher absolute numbers of sclerophyllous than riparian plant species were recorded, and the limitation on maximum richness
of strictly riparian species explains the negative slope in the regression between total species richness and strictly riparian plants. However, these results also indicate a constant presence of sclerophyllous species in riparian ecosystems, which may be explained by encroachment of upland species as a response to climate induced reduction in water levels in the upland habitats (Gasith and Resh 1999). This shift towards a water see more resistant community was also observed in the Tagus river system in Portugal (Aguiar et al. 2006). Alternatively, upland and exotic species are known to use riparian ecosystems for dispersal (Schnitzler et al. 2007), and some of those seeds could have become established either naturally or following disturbance (Aguiar et al. 2001). Spatial segregation between strictly riparian and sclerophyllous plant patches may be an important factor in determining propagule pressure from sclerophyllous plants species into riparian areas. My results however,
only show spatial segregation between BI 2536 purchase transects (between 2 km transects) and not within transects (between 200 m segments of each transect). These results may be explained by Thalidomide the heterogeneity of the riparian ecosystem itself at the finer scale (segments) and that of the landscape at the larger scale (transects). As both natural and human-mediated disturbances create gaps in the riparian ecosystem (Naiman and Décamps 1997; Salinas et al. 2000), this creates opportunities to the establishment of both riparian and sclerophyllous plants in similar locations (Tabacchi et al. 2002). Environmental variables associated with riparian plant richness Pollock et al. (1998) demonstrated that species richness in riparian ecosystems is a dynamic equilibrium between disturbance frequency and community productivity.