C. Nilsson et R. Jansson, FLORISTIC DIFFERENCES BETWEEN RIPARIAN CORRIDORS OF REGULATED AND FREE-FLOWING BOREAL RIVERS, Regulated rivers, 11(1), 1995, pp. 55-66
Riparian ecosystems are central elements in many landscapes because of
their shape, diversity and function as filters and corridors. They ar
e also among the environments most disturbed and threatened by humans.
Human-induced changes in riparian vegetation and flora were assessed
by comparing free-flowing and regulated rivers in northern Sweden. Alt
hough riparian vegetation structure is rather uniform along free-flowi
ng rivers, it varies distinctly along regulated rivers because of diff
erent water-level fluctuations in storage reservoirs, run of the river
impoundments and unimpounded but regulated reaches. The total species
richness of vascular plants per river in the riparian zone was simila
r between four free-flowing and four regulated rivers in northern Swed
en. However, species richness per 200 m long site was considerably low
er, and almost all groups of species were more species-poor per site i
n the regulated rivers due to perturbations caused by regulation. Both
free-flowing and regulated rivers showed an increase in the species r
ichness of ruderal plants towards the coast. In contrast, the species
richness of natural plants showed different longitudinal patterns in t
he two types of rivers, and differences were largest along the middle
reaches of the rivers. The reasons why responses in vegetation and flo
ra to human perturbation varied downstream along regulated rivers are
not known, but factors such as different disturbance patterns, irregul
ar distribution of remnants of former riparian soils and vegetation an
d differences in regional plant species richness and plant dispersal a
long the river corridor may be important.