Distribution of Helianthus paradoxus (Asteraceae) and Agalinis calycina (Orobanchaceae) on Bitter Lake National Wildlife Refuge, New Mexico, U.S.A.

Abstract

Helianthus paradoxus (Asteraceae) is listed as threatened under the U.S. Endangered Species Act (ESA), and Agalinis calycina (Orobanchaceae) is currently being considered for listing under the ESA. We surveyed H. paradoxus in 2018 and A. calycina from 2018 to 2020 in order to document their distribution and abundance on Bitter Lake National Wildlife Refuge (BLNWR), New Mexico. In 2018, H. paradoxus coverage was estimated to total 41.32 ha, with approximately 12,691,116 plants, and A. calycina coverage was estimated to total 1.45 ha, with approximately 107,338 plants. Approximately 0.56 ha of A. calycina coverage, totaling about 105,073 plants, fell in areas also mapped as H. paradoxus polygons. This accounted for about 39% of the A. calycina area in 2018. No A. calycina plants were detected in 2019, and in 2020 detections were limited to individual plants. BLNWR is one of only two areas where both plants occur, but A. calycina has a far more restricted distribution on BLNWR than H. paradoxus, occurring only in wetland management units. As with prior surveys, A. calycina abundance is highly variable from year-to-year. Periodic comprehensive surveys (once every 5 years) are needed in order to access status and trends. Further, we suggest that an index be developed that can characterize germination and establishment conditions for A. calycina into good, average, and poor conditions in order to meaningfully assess long-term trends.