Environmental extremes affect productivity and habitus of common reed in intermittent wetland

Abstract

This article describes the effect of extreme water level events and extreme temperatures on the primary productivity and habitus of the common reed (Phragmites australis) growing in lake and riparian habitats at intermittent Lake Cerknica between 2007 and 2021. At each sampling site, the above-ground biomass, leaf biomass and shoot density per m2, the number of internodes and leaves per plant, average shoot height, shoot basal diameter and the ratio of flowering plants per total plant number were determined. Stand and plant properties varied significantly between the locations, with exception of the basal diameter, that varied less. Biomass per area and per plant showed the trend of decrease across years, but the reed density remained at the same level. Redundancy analysis of the relationships between environmental parameters and productivity and habitus parameters revealed the importance for the lake stand of high-water level parameters in the 4th quarter of the previous year, while the 1st quarter of the current year was important for the riparian stand. High water level variables explained 60% of variance of productivity parameters of the lake stand and 21% of those of the riparian stand. For low water level parameters, the explained variance was 51 and 24%, respectively. In the case of habitus parameters, variances explained by high water level parameters were 66% for lake stand and 34% for riparian stand and of low water level parameters, the corresponding variances were 45% for lake stand and 59% for riparian stand. Temperature extremes can explain the lower variance. The interrelation between wetland hydrological extremes and reed stand/plant properties that was obtained suggests that an ecohydrological approach may provide a basis for successful management of reed-colonised wetlands.