Slower drawdown rates in lakes promote the growth and reproduction of lakeshore vegetation

Soil erosion on lakeshores due to the fluctuating water levels, waves, and other factors, remain a world-wide problem. Lakeshore vegetation can be helpful in preventing erosion. We investigated the effects of drawdown rate and depth on the growth and reproduction of a keystone lakeshore plant. We hypothesised that plants with access to water for longer would grow better and have higher reproductive output.We subjected 108 Spiny Sedge (Cyperus gymnocaulos) plants to six treatments comprising three drawdown rates (static, slow, fast) and two water depths (shallow and deep). We measured plant stem heights and numbers of flowers and bulbils weekly, and the initial and final biomass of the above ground and below ground components.Plants in treatments without access to water for long periods had the lowest growth and reproductive output. However, if the final water level was deep but drawdown was done slowly, plants were able to maintain similar growth and reproduction rates to plants with continuous access to water.Fluctuating water levels in lakes cause lakeshore plants at lower elevations to be inundated for longer and plants at higher elevations to be deprived of water for longer. Plants located at mid-elevations will thrive if their roots have access to water and their above ground parts are not fully submerged.Our findings are useful to water managers and ecologists concerned about preserving lakeshores from erosion by promoting vegetation. Both the rate and depth of drawdown should be considered in managing lake water levels. Where water levels fluctuate over large depths slower rates of drawdown will enable most plants to have access to water for longer, promoting their growth and reproduction, hence, reducing the lakeshore erosion. Keywords: lakes, vegetation, drawdown, erosion, sustainability