EFFECTS OF HARVESTING ON PLANT-COMMUNITIES DOMINATED BY EURASIAN WATERMILFOIL IN LAKE MINNETONKA, MN

Extensive mechanical harvesting has been used in 5,746 hectare Lake Mi nnetonka, Minnesota since 1989 to control populations of Eurasian wate rmilfoil (Myriophyllum spicatum). Approximately 47% of the 544 infeste d hectares were harvested during the summer of 1990. We measured effec ts of one series of harvests in five separate locations in Lake Minnet onka. Plant relative growth rates were greater (p = 0.001) in 54 m(2) harvested plots than in adjacent reference plots. The increased growth rate did not result in harvested areas having greater canopy density or higher total shoot biomass than adjacent reference areas. Harvestin g reduced total shoot biomass and plant abundance at the water surface for up to 6 weeks following harvest. Eurasian watermilfoil was the do minant plant in all areas, although its presence in an area was not co rrelated with high total shoot biomass in that area. Total shoot bioma ss was positively correlated with both water clarity and percentage of sediment organic matter and negatively correlated with the percentage of clay in the sediments.