Historical changes in abundance of floating-leaf and emergent vegetation in Minnesota lakes

Abstract.—To assess the consequences of shoreline development, whole-lake vegetation abundance of dense floating-leaf and emergent vegetation in 100 north-central Minnesota lakes was estimated from aerial photographs for selected years between 1939 and 2003. Lakes were randomly selected from three shoreland development classifications, which define statewide minimum shoreline development standards for Minnesota. The three classes, in order of increasing restrictions for development, are general development, recreational development, and natural environment. Image analysis techniques were used to estimate vegetation abundance (percent cover). Shoreline development varied by shoreland development class. Floating-leaf and emergent vegetative cover (percent of lake surface area) was significantly affected by development. Increases in shoreline development, indexed by dock sites per shoreline kilometer, reduced plant cover. A linear mixed-effects model estimated that in 2003, the mean floating-leaf and emergent vegetation cover loss from development was 6 % for natural-environment lakes, 14 % for recreational-development lakes, and 17 % for general-development lakes. Total vegetation cover loss for north-central Minnesota lakes was estimated at 15%. Shoreline regulatory policies may need to be changed or riparian owner incentive programs added to address cumulative impacts to fish and wildlife habitat. Increases in shoreland development are changin