Effects of geothermal activity and invasive grasses on the conservation of a critically endangered plant in Hawaiʻi

Keywords: rare plants, volcanoes, conservation, biogeography, Hawaii
Session Type: Virtual Poster Abstract
Day: Sunday
Session Start / End Time: 2/27/2022 02:00 PM (Eastern Time (US & Canada)) - 2/27/2022 03:20 PM (Eastern Time (US & Canada))
Room: Virtual 38

Abstract

One of the most pressing environmental issues today is the loss of biodiversity resulting from human-caused extinctions of myriad species, including (importantly) plants. The Hawaiian Islands have experienced numerous plant extinctions and offer an important setting for studying the conservation of threatened plants facing rapid environmental change across many facets. Many extinctions occur due to land use change, climate change, and introductions of invasive species. We aimed to study the relationship between an endangered plant and multiple biotic and abiotic variables as a case study for understanding the relationship between a rapidly changing environment, invasive species impacts, and conservation efforts for a species of concern (in our case, Portulaca scelorcarpa).We monitored a census of 211 P. sclerocarpa in a geothermal area, including 175 individuals that we outplanted across biophysical gradients including soil temperatures and abundance of invasive grasses. We analyzed the data using binomial regression and path analysis to determine the influence of biophysical variables on P. sclerocarpa mortality over four years. We found a sharp decline in population abundance (0.3% of the population size recorded in the 1980s) that coincided with shifting geothermal heating of the soil and the introduction of invasive grasses. Outplantings had highest survivorship (>55%) in moderately warm soils. Our experiment revealed that a niche may exist where soil temperatures are too hot for invasive grasses, but still tolerable for P. sclerocarpa, and that a large portion of P. sclerocarpa mortality was associated with exceedingly high soil temperatures or high abundance of invasive grasses.