Threatened and Endangered Plant Surveys of Northwest Field

Abstract

In 2015, fourteen plant species were added to the federal list of Endangered and Threatened Wildlife and Plants from the Marianas, joining Serianthes nelsonii, which was federally listed as endangered in 1998. Approximately 200 acres of non-contiguous limestone forest habitat at Anderson Airforce Base (AAFB), Northwest Field (NWF) were surveyed to determine distribution and abundance of these species. State of the art GIS techniques were employed to carry out 5-10m wide transects throughout the entire survey area from November 2016 through January 2017. Of the thirteen listed plant species known from limestone forests, only six (Cycas micronesica, Dendrobium guamense, Eugenia bryanii, Heritiera longipetiolata, Tabernaemontana rotensis, Tuberolabium guamense) were recorded during the survey on both subdued and pinnacle eogenetic karren habitats. High densities of the threatened species Cycas micronesica (total count of 12,505) were observed throughout the survey area, and an almost continuous band of the threatened species Eugenia bryanii (total count of 228) was found along the cliff line. However, both species are vulnerable to various existential threats, including invasive ungulates and invertebrates. Of the three listed epiphytic orchids, Tuberolabium guamense (total count of 1,684) was observed at high densities in limited areas. T. guamense grows mainly on understory tree species, which can regenerate under ungulate pressure, but still needs canopy trees to provide shade. Other orchid species like Dendrobium guamense (total count of 21), which was relatively rare, grew on outer branches of large canopy trees. Bulbophyllum guamense was not observed. An increase in the number of intense storms and lack of regeneration of phorophytes (plants on which an epiphyte grows) are likely contributing to their scarcity. The endangered Heritiera longipetiolata (total count of 12) and the threatened Tabernaemontana rotensis (total count on 125) occurred in very low numbers. Given the presence and scarcity of some of these species, habitat protection and the implementation of conservation management practices are recommended in the survey area and adjacent habitats.