Many riparian ecosystems in northern Sweden have been impacted by structural measures to facilitate timber floating from the 19th and into the second half of the 20th century. Restoration efforts in the last decades included relocation of boulders into the channel, dam and stone pier removal, and opening of cut-off side channels. The present projects assesses where in a river catchment it is most effective to realize such restoration efforts. This is done by measuring the responses to restoration of basic ecological processes in a climatic and a stream order gradient. A total of 10 sites, each consisting of a pair of an impacted and a restored reach, were selected in the tributaries and the main channel of the Vindel River catchment. We employed the phytometer approach by transplanting the forb Filipendula ulmaria and the grass Molinia caerulea into the field and recording their reactions to the present conditions. Furthermore, germination and performance studies on soil extracted from the different sites were conducted in the greenhouse, and soil samples were analyzed to yield information about levels of plant nutrients.
Results/Conclusions
Preliminary results from the field experiment after the first two growing seasons show a high between-site-variation and no clear patterns, neither in regard to the different gradients nor in terms of improvement of habitat conditions at restored sites. When comparing phytometer performance in the greenhouse, however, we detected that plants grown on soil extracted from restored sites responded with an almost significantly higher biomass production (P=0.08). Performance was especially high on soils from a higher elevation in the riparian zone, i.e. in a zone that is less frequently flooded. Environmental factors affected the different phytometer species differently. The biomass production of the forb, for example, was significantly correlated with length of vegetation period, whereas the grass showed a significant correlation with the amount of organic material present in the soil. We conclude that phytometers in the field will need more time to show clear patterns, particularly at a lower elevation in the riparian zone where flooding lasts longer and is more frequent, implying a shorter effective vegetation period. Furthermore, there seems to exist a “memory effect” of the vegetation period in the soil that we hope a chemical analysis of the soil can shed some light on.
