Functional and taxonomic diversity indices of riparian plants in river networks

1. The River Continuum Concept (RCC) predicts a gradual shift of
organisms’ functional adaptations along the longitudinal
(upstream-downstream) gradient, as well as the maximization of the biotic
diversity in mid-reaches. Although this theoretical framework was
originally developed for stream macroinvertebrates, we tested whether such
a pattern can be also observed in riparian plant communities. 2. We
studied the cover of plant species in riparian forests across two river
networks. We analyzed the taxonomic and functional diversity indices, as
well as community-weighted means of functional traits in relation to the
plots’ position in the catchments. 3. The observed patterns were largely
in line with the predictions of RCC. We discovered a significant decrease
in the specific leaf area and an increase in the herbaceous plants’ height
in communities along a river gradient. There was also a shift in the
dispersal syndromes, towards a higher importance of zoochory in the lower
reaches. 4. The functional richness and divergence displayed unimodal
patterns of increasing values in the mid-reaches. The patterns of
taxonomic diversity were similar, but some plots in the lowest reaches
were more diverse than expected, forming an additional increase in
diversity. 5. The study shows that plant communities in natural riparian
forests show high connectivity along the longitudinal gradient, which
along with the environmental gradients creates patterns that are known
from theoretical predictions.