Restoring two threatened Physaria species in the Piceance Basin of northwestern Colorado

Physaria congesta and Physaria obcordata are rare plants endemic to the Piceance Basin of northwestern Colorado, USA. Since the Federal listing of both species in 1990, management efforts have focused largely on protecting critical habitat. However, this unique habitat is also a prime energy development area, necessitating additional measures to protect and restore both species. The overall objective of my research is to determine the best approach for establishing new populations of P. congesta and P. obcordata in suitable but unoccupied habitats in the Piceance Basin.
To address this objective I used 3 methods: a soil feedback experiment, a field ecological survey, and a field establishment experiment. In recent years it has been shown that relative abundance of some species is strongly correlated with plant soil feedbacks and rare species can demonstrate strong negative feedbacks with pathogens from their own root systems (Klironomos 2002). Based on this theory I conducted a 12-week soil feedback study using field soil as inoculum collected from occupied and unoccupied suitable sites. I found no significant differences in estimated biomass between occupied status of either species.
To further investigate the differences between occupied and unoccupied sites I conducted a field ecological survey, building upon previous habitat suitability research, comparing plant cover, soil color, and soil/air temperature differential. I found significant differences between occupied and unoccupied sites for both species in multiple parameters (P. congesta = aspect, elevation, percent bare ground and rock, and soil color; P. obcordata = slope and soil color). Within occupied sites I found a negative correlation between P. congesta density and slope as well as a positive correlation between P. obcordata density with increased forb cover (< 5%) and decreased bare ground and rock cover (between 80 and 90%).
The final phase of my research, which was delayed for a year due to legal issues, was to establish field plots, where I seeded and transplanted both species during fall 2014. Additional plants were transplanted during spring 2015. Initial germination and establishment rates, was collected spring 2015 where I found limited germination of seeded plots and moderate survival of fall transplants. Early trends show that P. obcordata is performing better than P. congesta and transplants are more successful than seeds. Within P. obcordata sites, far sites are performing better than near sites. Long term monitoring of these sites will expand our understanding of the restoration potential of these species. Results from this research will assist land managers to make informed decisions regarding future protection and restoration of these species.