Use of ecological indicator values to investigate successional change in boreal to high-alpine glacier-foreland chronosequences, southern Norway

Abstract

Mean weighted Ellenberg indicator values were calculated for vegetation recorded from four successional stages on 39 glacier forelands in the Jostedalsbreen and Jotunheimen regions of southern Norway. The sites ranged in altitude from 80 to 1860 m a.s.l. Results revealed a trend of decreasing mean indicator values for light, reaction and nitrogen on successively older terrain. Mean indicator values for moisture did not show a consistent pattern of variation according to successional stage. When stratified according to altitude, sub-alpine and boreal sites showed the most rapid decrease in pH and productivity levels through time. Within this altitudinal zone, mean values after 70 years of succession were already indistinguishable from those for the mature vegetation. At higher altitudes, in the alpine zone, a more gradual decrease was detected but culminated in similar values. A significant trend in decreasing indicator values for light with succession was found at all except the high-alpine sites where the value for mature vegetation was not significantly different from that for earlier stages. Also evident was the greater decrease in mean value for light at the lowest altitudes, reflecting the establishment of a birch-woodland canopy. Use of snowmelt indicators improved interpretation of the differences between late-successional stages according to altitude. Variance partitioning revealed that differences between successional stages accounted for 29% of the variation in mean indicator values, whereas altitude accounted for an additional 12%. Indicator values have provided a useful comparison of rates of succession and associated vegetation development within different altitudinal zones, inferring possible mechanisms of change at a regional scale.