Data from: Vegetation patterns in small boreal streams relate to ice and winter floods

1. In-stream and riparian vegetation is species-rich, productive and
dynamic. Its patterns in small boreal streams are largely driven by
seasonal flow regimes. Traditionally, flow-related processes during the
growing season, particularly the spring flood, have been seen as the most
important, whereas vegetation has been viewed as being dormant and ‘less
affected’ during winter. 2. Riparian and in-stream vegetation was
inventoried during the summers 2011‒2013 in eight reaches of northern
Swedish streams. Along each reach the ice formation was surveyed during
winter by visual inspections and with permanently placed cameras. We then
evaluated the potential effects of ice regimes and winter flooding on
riparian and in-stream vegetation during 3 years by relating the abundance
of winter floods caused by anchor-ice to the cover, composition and
biomass of vegetation. 3. We found that the numbers of winter floods were
higher along reaches with anchor-ice formation than in reaches without. We
also found that species diversity of riparian vegetation was higher in the
reaches with anchor-ice. This resulted from a lower cover of riparian
dwarf shrubs and a higher cover of graminoids and forbs along reaches with
anchor-ice. We also found a lower cover of in-stream algae but a higher
cover of bryophytes in anchor-ice reaches. These patterns were consistent
throughout the study period although there were interannual differences in
temperature, water levels and ice cover. 4. During our study period, we
encountered an average of 20 shifts per winter between freezing and
thawing, while there was an average of 10 shifts per winter during
1960‒1990. This indicates a warming climate in high latitudes. Higher
temperatures and more shifts between freezing and thawing may initially
increase ice dynamics. However, with further increases in mean temperature
ice production should eventually decrease. 5. Synthesis. Ice and winter
floods caused by anchor-ice appear to be important disturbance agents that
allow less competitive species to establish along small boreal streams. If
ice dynamics is reduced, the composition and production of riparian and
in-stream vegetation may be changed, with possible consequences for the
entire stream ecosystem.