Big sagebrush in a changing climate context: The effects of genotype and climate variability on success of sagebrush seedlings

Background/Question/Methods

The loss of big sagebrush (Artemesia tridentata) due to wildfire has motivated efforts to restore it through seeding and planting. Restoration success has been mixed, despite large investment. Big sagebrush displays high intraspecific diversity, and appropriate seed source is an increasing management concern in post-fire restoration. Currently, there are unmet data needs for establishing seed transfer zones for big sagebrush under future climate regimes and a major pending question is whether seeds sources from warmer and drier sites will be better suited than local seed sources. Our primary objectives in this study were to assess climate responsiveness of seedlings of different provenances on burned areas and relate ecophysiological-climate adaptation in seedlings to that of established plants from a common garden study.  Experimental passive warming chambers paired with unwarmed control plots were installed at Birds of Prey National Conservation Area on five sites burned in 2012. We evaluated eleven different seed sources of big sagebrush from all three subspecies, dissimilar climates of origin, and different ploidy levels to assess how genotype affects initial establishment of sagebrush.  A suite of dependent variables were measured; including survival, growth, chlorophyll fluorescence, isotopic assessment of water-use efficiency, and differential thermal analysis.

Results/Conclusions

Preliminary results suggest that experimental warming enhanced overall seedling survival revealing the sensitivity of sagebrush to temperature (particularly daily minima). Among the three subspecies of sagebrush, basin big sagebrush had the lowest mortality under warming, which may relate to access to deeper soil water resources (p=0.001). Overall, we did not observe consistent strong support for local adaptation. Local genotypes exhibited greater stress and photoinhibition after freezing and light treatments than distant genotypes (p=0.01).  Isotopic assessment of water-use efficiency of distant vs. local seedlings revealed that seedlings from warmer and drier climates have greater water use efficiency under current climate conditions (p=0.04). During initial establishment, there is an emerging pattern that implies a tradeoff between growth and survival. Genotypes with most overall growth also had the highest overall mortality, and this trend contrasts patterns observed in more mature sagebrush. These findings indicate the importance of drawing inference on ecophysiological adaptation from multiple demographic stages while establishing seed transfer zones for big sagebrush restoration.