Searching for a needle in a haystack: Using GIS to identify likely locations of previously unknown populations of an endangered species

Background/Question/Methods

Finding extant populations of rare and endangered species is a problem faced in both conservation and management.  An accurate evaluation of species abundance is necessary to assess the status of a species.  This is complicated in rare species with patchy, disjunct distributions.  Global Information Systems (GIS) can help narrow the search area by identifying the physical characteristics of habitats where extant populations are found, then identifying locations with similar attributes.  Astragalus brauntonii is federally listed endangered plant found along the foothills of southern California.  This species is adapted to moderate rates of disturbance (e.g. - erosion prone sandy slopes) and responds to fires with mass germination events.  Wildfires in 2005 revealed previously unknown populations.  This suggests other populations may be hidden in the seed bank, but where?  Digital elevation models (DEMs), soil, and climate data were used to assess the features suitable for A. brauntonii using extant populations as a guide.  Aspect, slope, and insolation were calculated using DEMs.  These characteristics along with soil and precipitation data were then used to identify locations in the Santa Monica and Santa Susana Mountain ranges with suitable habitat. 

Results/Conclusions

The analysis indicated that A. brauntonii was most frequently found on rocky, sandy hillsides with a 5-20 degree slope.  Though there was no clear aspect preference, insolation figures demonstrated a preference for moderately sunny locations.  A. brauntonii was found in a few soil types, most of which are partially derived from ancient marine sediments.  Of the 6210 km² in the studied area, less than 3.25% was found to be marginally suitable or better.  This habitat has a patchy distribution, but suggests that unidentified populations may exist south of Thousand Oaks and north of Ventura.  Seed bank studies may confirm this result.  If a seed bank exists or the area is suitable, populations of this plant could be restored to those locations and monitored to confirm if this plant could survive there.  If so, these locations may be considered in the restoration efforts for this endangered plant.  Restoration of A. brauntonii on this land might also be used to mitigate habitat loss elsewhere.