Long-term change in Wisconsin lake plant communities

Long-term changes in Wisconsin lake plant communities were assessed with th e floristic quality index (FQI) and the aquatic macrophyte community index (AMCI). Only plant communities in natural lakes were studied, by ecoregion and water source. The median number of species (N) and the median FQI incre ased over time in Northern Lakes and Forests ecoregion lakes with and witho ut inlets and North Central Hardwood Forests ecoregion lakes without inlets . The median N declined in Southeastern Wisconsin Till plains lakes with in lets and median N and median FQI declined in Southeastern Wisconsin Till Pl ains lakes without inlets. No significant change in median N or FQI values was found in North Central Hardwood Forests ecoregion lakes with inlets. No rthern Lakes and Forests ecoregion lake plant communities increased in qual ity using median AMCI values. No other ecoregion-lake type showed a signifi cant change over the time period analyzed. Regression analysis showed that four of 33 lakes showed a significant trend of quality change using FQI val ues, and seven of 28 lakes showed a significant trend of quality change usi ng AMCI values. Only one of the AMCI trends was negative; all other AMCI an d FQI trends were positive Although this study indicates no strong or wides pread decline in aquatic plant communities, results should be interpreted w ith caution because declines may have occurred before sampling began, incre ased plant quality may indicate degradation of other water-quality paramete rs, and the length of record for many lakes is short.