Rising from the ashes: Determining local adapation in an endangered plant

Background/Question/Methods

Astragalus brauntonii is a short-lived, perennial plant found in the coastal sage communities in the foothills around the Los Angeles basin.  This disturbance adapted species invests energy in producing a tremendous number of seeds that remain dormant in the soil.  Most of the current understanding of this endangered, disturbance adapted plant is based on work conducted in one coastal population.  Brush clearing and recreational use creates moderate rates of disturbance allowing the population to be maintained above ground.  Infrequent disturbances inland make those populations difficult to study.  In 2005, a series of wildfires in Southern California created a wide scale disturbance that allowed multiple populations to emerge from the seed bank throughout its range.  Six populations on three soils were studied to learn more about these ephemeral inland populations and identify differences between inland and coastal populations that could potentially impact management decisions.  Thirty plants at each of six populations were tagged and the vegetative growth and reproduction was monitored for 3 years.  The fruit and seed production was counted in 2008 and infructescence counts were maintained for subsequent years. 

Results/Conclusions

In 2008, there were significant differences in vegetative growth including the height (p<0.008), diameter (p<0.002), leaf number (p<0.002), and the number of branches (p<0.001).  However, in 2009 only height was significantly different (p<0.03) while diameter and number of leaves were marginally significant (p<0.09).  In 2008, the number of inflorescences per plant among populations did not varied significantly (p>0.27), though it was marginally significant in 2009 (p<0.07).  The number of flowers per raceme varied among populations (p<0.0001) as did the number of seeds per fruit (p<0.0001) resulting in greater reproductive output in some populations.  A common garden study that included only four populations suggests that some traits are inherited, but show evidence for local adaptation in only one population.  Three populations demonstrate fixation for some traits that suggests genetic impoverishment.  Though it may be safe to introduce seeds among genetically depauperate populations, one population should be managed separately to maintain its local adaptation.