The shift from a turbid-water state to a clear macrophyte-dominatedstate in the shallow lake Veluwemeer (The Netherlands) has led to nuisance forrecreational navigation. The nuisance concerns the dense beds of Potamogeton perfoliatus in particular, whereas thelow-canopy forming charophytes cause much less harm. On the other hand, theimportance of macrophyte cover for the stability of the clear-water state hasbeen recognised. To assess the potential of mechanical removal of densemacrophyte beds, several cutting regimes were simulated in a mixed vegetation of P. perfoliatus and Chara aspera , usingthe individual-based model Charisma. These species occupy a wide range of waterdepths between 0.5 and 2.5 m, with C. aspera dominating the shallower zone and P. perfoliatus dominatingthe deeper zone; intermediary is a zone where either species may dominate asalternative equilibria. Both the cutting height and timing affected the amountof biomass present in summer. The effect of cutting was more profound fortreatment later in the season. With a cutting level above the Chara -canopy, the simulations showed an increased biomassof C. aspera and reduction of P.perfoliatus . In the zone of alternative equilibria, it was possibleto provoke a sustainable shift from P. perfoliatus dominance to C. aspera dominance. To achieve this, annualrepetition of cutting for a number of years was necessary. A harvesting regimeaimed at shifting the vegetation dominance from P.perfoliatus towards C. aspera could be an optionfor management of the lake, since it holds the perspective of decreasedmanagement effort after a number of years. Moreover, removing only high-canopyvegetation implies high conservation values and recreational use can becombined.
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