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Riparian corridors in Mediterranean-climate regions (med-regions) are resource-rich habitats within water-limited, larger landscapes. However, little is known about how their plant communities compare functionally and compositionally across medregions. In recent decades, research on these ecosystems has expanded in both geographic scope and disciplinary depth. We reviewed 286 riparian-vegetation studies across the five med-regions, and identified common themes, including: (1) high levels of plant biodiversity, structural complexity, and cross-region species introductions; (2) strong physical controls on plant demographics and community structure; and (3) intensive human impacts. European and Californian ecosystems were the most represented among the studies reviewed, but Australia, South Africa, and Chile had the greatest proportional increases in articles published since 2000. All med-regions support distinct riparian flora, although many genera have invaded across regions. Plant species in all regions are adapted to multiple abiotic stressors, including dynamic flooding and sediment regimes, seasonal water shortage, and fire. The most severe human impacts are from land-use conversion to agriculture, streamflow regulation, nutrient enrichment, and climate change. Current knowledge gaps and subjects for future research include cumulative impacts to small, ephemeral streams and large, regulated rivers, as well as understudied ecosystems in North Africa, the western Mediterranean basin, and Chile.Electronic supplementary material The online version of this article (

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Abstract. Mechanical damage by floodwaters is frequently invoked to explain the distribution of riparian plant species, but data have been lacking to relate vegetation to specific estimates of flood damage potential. This research uses detailed estimates of unit stream power (an appropriate measure of the potential for mechanical damage) in conjunction with vegetation cover data to test this relationship at 37 valley‐bottom sites in the Transverse Ranges of Southern California. A computer program, HEC‐2, was used to model the slope and the variation in flow depth and velocity of the 20‐yr flood across the sites. Regression models tested the influence of stream power (and of height above the water table) on the woody species composition of 393 4‐m cross‐section segments of the valley‐bottom sites. Results indicate that unit stream power does have a significant effect on the riparian vegetation, but that the amount of that influence and its importance relative to the influence of height above the water table varies between watersheds. Some species are found primarily in locations of high stream power, while others are limited to portions of the valley bottom that experience only low stream power.

. Biodiversity varies considerably in Southern Californian riparian vegetation. The intermediate disturbance hypothesis posits greatest diversity in settings that are subject to moderate‐intensity disturbance. Flood intensity tends to vary systematically in watersheds, potentially imposing patterns of biodiversity. In two study watersheds, species richness increases with flood severity. Diversity, or heterogeneity, is less predictable: Biodiversity patterns in these watersheds are complicated by atypical patterns of flood severity. Although riparian diversity may be intimately dependent on flood disturbance, the relationship is predictable only with due attention to the physiographic details of individual stream networks.