Original ResearchRiver regulation may filter out riparian plants often resulting in reduced functional
diversity, i.e., in the range of functions that organisms have in communities and
ecosystems. There is, however, little empirical evidence about the magnitude of such
reductions in different regions. We investigated the functional diversity patterns of
riparian woody vegetation to streamflow regulation in boreal Sweden and Mediterranean
Portugal using nine plant functional traits and field data from 109 sampling sites.
We evaluated changes in mean plant functional traits as well as in indices
of multidimensional functional traits, i.e., functional richness (FRic) and functional
redundancy (FRed) within regions and between free-flowing and regulated river reaches.
We found that regulation significantly reduced functional diversity in Sweden but not in
Portugal. In Sweden, the increased magnitude of variations in water flow and water
level in summer, the prolonged duration of extreme hydrological events, the increased
frequency of high-water pulses, and the rate of change in water conditions were the
likely main drivers of functional diversity change. Small riparian plant species with tiny
leaves, poorly lignified stems, and shallow root systems were consistently associated
with regulated sites in the boreal region. In Portugal, the similar functional diversity values
for free-flowing and regulated rivers likely stem from the smaller streamflow alterations
by regulation combined with the species legacy adaptations to the Mediterranean
natural hydrological regimes. We conclude that streamflow regulation may reduce the
functional diversity of riparian woody vegetation, but the magnitude of these effects will
vary depending on the adaptations of the local flora and the patterns of streamflow
disturbances. Our study provides insights into functional diversity patterns of riparian
woody vegetation affected by regulation in contrasting biomes and encourages further
studies of the functional diversity thresholds for maintaining ecosystemsinfo:eu-repo/semantics/publishedVersio