Quantifying the population response of invasive water hyacinth, Eichhornia crassipes, to biological control and winter weather in Louisiana, USA
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Water hyacinth, Eichhornia crassipes, is an invasive, tropical, aquatic plant that has caused significant environmental and economic damage since its establishment in Louisiana, USA, in 1884. Both invasion control programs and freezing temperatures are known to negatively affect water hyacinth populations; however, the combined impact of these factors on water hyacinth population dynamics has not yet been quantified, thereby limiting the ability to isolate the effectiveness of biocontrol and other types of control under variable weather conditions. We built a seasonal logistic population model that included time-varying intrinsic growth and overwinter mortality parameters which were estimated by fitting the model to vegetation survey data. We estimated that annual overwinter mortality rates declined from a peak of 71 % in 1977 to the time series low of 11 % in the winter of 1992, followed by an average of 28 % per year from 1993 to 2013. After accounting for the magnitude and trend of overwinter dieback events, our model predicted that the intrinsic growth rate of the Louisiana water hyacinth population declined by 84 % between 1976 and 2013. Despite higher average winter temperatures in recent decades, the population has not rebounded. Our study reveals the dramatic effectiveness of Louisiana’s biological control program to successfully suppress water hyacinth invasion.
KeywordsBiological control Eichhornia crassipes Louisiana Logistic growth Water hyacinth
We thank Alexander Perret, Michael Harden, and Richard Brassette (ret.) of LDWF for providing vegetation survey data and information about Louisiana’s water hyacinth control program. We also thank Anna McMurray for assistance in compiling the data, and Michael Wilberg and Dong Liang for constructive modeling discussions. Funding was provided by the US Army Corps of Engineers Aquatic Plant Control Research Program, under management of Dr. Linda Nelson. This is contribution number 5184 of the University of Maryland Center for Environmental Science.
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