Data from: Time for recovery of riparian plants in restored northern Swedish streams: a chronosequence study

A lack of ecological responses in stream restoration projects has been
prevalent throughout recent literature with many studies reporting
insufficient time for recovery. We assessed the relative importance of
time, site variables, and landscape setting for understanding how plant
species richness and understory productivity recover over time in riparian
zones of northern Swedish streams. We used a space-for-time substitution
consisting of 13 stream reaches restored 5–25 years ago, as well as five
unrestored channelized reference reaches. We inventoried the riparian zone
for all vascular plant species along 60-m study reaches and quantified
cover and biomass in plots. We found that while species richness increased
with time, understory biomass decreased. Forbs made up the majority of the
species added, while the biomass of graminoids decreased the most over
time, suggesting that the reduced dominance of graminoids favored less
productive forbs. Species richness and density patterns could be
attributed to dispersal limitation, with anemochorous species being more
associated with time after restoration than hydrochorous, zoochorous, or
vegetatively reproducing species. Using multiple linear regression, we
found that time along with riparian slope and riparian buffer width (e.g.,
distance to logging activities) explained the most variability in species
richness, but that variability in total understory biomass was explained
primarily by time. The plant community composition of restored reaches
differed from that of channelized references, but the difference did not
increase over time. Rather, different time categories had different
successional trajectories that seemed to converge on a unique climax
community for that time period. Given our results, timelines for achieving
species richness objectives should be extended to 25 years or longer if
recovery is defined as a saturation of the accumulation of species over
time. Other recommendations include making riparian slopes as gentle as
possible given the landscape context and expanding riparian buffer width
for restoration to have as much impact as possible.