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Viability of Silphium albiflorum in Tarrant County

Post Oak & Prairie Journal 

Volume 1, No. 3  Page 14 

Maria Arreola, Patricia Coronado, Alex Hendee, Morgan Kirkpatrick, Sophie Nadolski, Fauz Saheb, Stefan Self, Yasmine Sharif, Philip Trammell, Bruce Benz*, Texas Wesleyan University Biology Department, Fort Worth, TX 

Abstract

White Rosinweed (Silphium albiflorum A.Gray: Asteraceae) is a Texas endemic vulnerable to extinction in Tarrant County, TX. Habitat fragmentation due to urban growth has reduced its geographic extent in Tarrant County and surrounding areas. Population viability analysis in 2014 includes estimates of net reproductive value for the 3,301 individuals in 179 metapopulations from four of the known Tarrant County protected natural area localities. Two localities with fewer than five metapopulations each were not surveyed. Less than one third of the metapopulations surveyed had net reproductive values greater than one (1.0) suggesting they are not reproducing effectively. The Benbrook Lake Longhorn Buffer Zone locality shows the lowest rate of increase; only two of 38 metapopulations show recruitment. White Rosinweed appears to be critically endangered in Tarrant County because there is 1) an observable reduction in numbers of individuals, 2) the total geographic area occupied by the species is declining, 3) the number of mature individuals currently alive is small, and 4) two localities have fewer than 250 mature breeding individuals.