Most desert perennial plants operate at the borderline of hydraulic failure, and modeled climatic trajectories for precipitation are expected to push the native flora beyond such an ecological line of survival. The risk is particularly high in species that gauge soil moisture availability as a cue for seed germination and shoot apical meristem growth and flowering. In the native range of the desert herbaceous perennial "Cryptantha flava" (Boraginaceae), the Great Basin desert, climatic models predict an increase of precipitation at the end of the growing season.
We explored the demographic viability of "C. flava" in the light of future climate change. We supplemented 45 mm of water every August of 2006 through 2009 to plots containing +3000 individuals ranging in size and development. We followed their demographic dynamics and compiled them in projection matrices to study the effect of the watering treatment. We also studied their module demographic dynamics because previous work revealed that the adults of this species are hydraulically sectored (they behave as a group of independent modules) and wanted to understand if watering would affect each module differently. We measured for April and August of each subsequent year, until 2010, the whole-plant and within-plant module-specific rosette birth, growth, mortality and turnover, as well as number of seeds produced, and their posterior recruitment.
Results/Conclusions
The analysis of the long-term demographic censuses using periodic projection matrices revealed increases in population growth rate the year following the watering treatment in comparison to the control plots, followed by a marked decline in the years after. This pattern was primarily attributed, via life table response experiment analyses, to the growth of already established individuals, which then experienced drastic shrinkage, as well as a decrease in the recruitment rate of seedlings two years after the treatment. The flowers created the year following each watering treatment contained more seeds, and yet the seedling recruitment the following years was lower in treatment plots. This research reveals the challenges that natural populations of desert perennial plants will face in the future, and how differential signaling of environmental cues via changes in climate can push populations away from their natural demographic equilibria.
