EFFECTS OF FLOODING AND TRAMPLING ON THE PERFORMANCE OF RIVER FORELAND SPECIES OF RUMEX AND PLANTAGO

The effects of a combined regime of flooding and trampling on survival , growth and reproduction of some species from river forelands, were s tudied in a large-scale, outdoor experiment. In additional pot experim ents, trampling effects were separated into effects of shoot damage an d of soil compaction. Resistance of individual leaves to a tearing for ce and recovery from damage were measured. Species were selected accor ding to their occurrence in the field in relation to trampling and flo oding: Rumex acetosa from seldom flooded, extensively trampled sites; R. crispus from frequently flooded, non-trampled sites; Plantago major ssp. pleiosperma from regularly flooded, non- to heavily-trampled sit es and P major ssp. major from seldom flooded, very heavily trampled s ites. Only R. crispus showed obvious morphological adaptations to floo ding but their significance was vastly reduced when flooding was combi ned with trampling. Although they did not possess any important morpho logical adaptations, both Plantago subspecies survived flooding. Of bo th Plantago subspecies, P major ssp. pleiosperma performed better than P. major ssp. major when soil compaction resulted in hypoxia. P. majo r ssp. major, responded better when the major effect was an increase i n penetrometer value. R. acetosa was negatively affected by trampling, flooding and the combination of both. Flooding inhibited flowering du ring the experiment and trampling reduced seed production. In the pot experiment no interaction was found between shoot damaging and soil co mpaction due to trampling. Responses to shoot trampling could largely be explained by the tearing resistance in combination with the recover y characteristics of the species. Species occurring on more trampled s ites in the held had a higher resistance to tearing stress and a bette r recovery after shoot damage.