The Ecology and Conservation of Texas wild-rice (Zizania texana), a Federally Listed Species

Texas wild-rice (Zizania texana) is a globally rare (G1), and federally listed endangered aquatic grass consisting of one population located in the upper 4 km of the San Marcos springs system of central Texas, U.S.A. Texas wild-rice is a unique aquatic grass. Unlike other members of the Zizania genus Texas wild-rice can grow both perennially submerged or as a short lived perennial in an emergent, and sexually reproductive, form. It is highly reliant on the thermally stable and clear spring-fed water of the San Marcos River. Although early historical writings from the early 1900’s indicate Texas wild-rice was abundant and a nuisance to irrigation pumping from the river. By the 1960’s the species had dwindled to around 150 individual plants and its rapid decline was first documented by W.H. Emory. Its population was impacted from poor water quality and river dredging at the time. It was one of the first plants placed onto the amended Endangered Species Act in 1978. Through the 1980’s an annual mapping and monitoring plan was put into place by Texas Parks and Wildlife Department. Annual monitoring by department biologists showed the population rebounded moderately into several thousand square meters, however sexual reproduction was functionally absent and competition was increasing from introduced aquatic plants including Hydrilla verticillata, Hygrophila polysperma, and Colocasia esculenta. Through the 1990’s and early 2000’s the population extent remained mostly unchanged. In this time an ex situ refugium was developed at the San Marcos National Fish Hatchery, spearheaded by the United States Fish and Wildlife Service, to hold plants and conduct research. From 2000 to present BIO-WEST began monitoring the species annually on behalf of the Edwards Aquifer Authority. In 2013 a large-scale restoration and conservation strategy for Texas wild-rice in situ was implemented through the Edwards Aquifer Habitat Conservation Plan (EAHCP) that is funded by Edwards Aquifer Authority groundwater pumping fees. Due to its unique growth needs ex situ conservation practices are severely limited. The species’ condition has vastly improved in the 12 years since this program has been implemented. However, recreation and river use has always limited extent coverage of the plant to an unknown degree. During the Covid pandemic of 2020, also known as the Anthropause, recreation and river use was restricted for a period of over 8 months. The Anthropause provided a unique opportunity to gather observations and data for the species in the absence of recreational pressure. Finally, removal of competitive invasive plant species, restorative plantings as well as protective buffer zones have all been creative ways utilized to conserve the species in its habitat. Texas wild-rice has now become the dominant aquatic plant in the San Marcos River with sexual reproduction common place.