A new approach towards climate monitoring in Rocky Mountain alpine plant communities: A case study using herb-chronology and Penstemon whippleanus

Abstract

The alpine ecosystem of the Rocky Mountains is experiencing significant increases in growing season length, summer maximum temperatures, and shifting patterns in precipitation. Alpine herbs are specifically sensitive to these changes. Biomass accumulation and reproductive effort are often negatively affected by elevated temperatures and earlier snowmelt. Here, we assess the use of herb-chronology, the study of annual growth rings in the woody underground organs, to retroactively monitor effects of monthly to seasonal climate on growth of the alpine forb species Penstemon whippleanus. We explored methods for building the strongest growth chronology possible by comparing the mean interseries correlations (MICs) of the whole population to that of groupings by cohorts, spatial locations, and random groupings using a permutation procedure. MIC for the whole population was low (0.034). Our permutation grouping performed best, producing a maximum MIC of 0.263. Using the permutation-derived chronology (2008–2015), we found significant decrease in growth with increased maximum temperatures in July, decreased May rainfall, increased drought between April and August, and lower minimum temperatures in September. Herb-chronology proved useful for understanding growth dynamics with climate in this alpine system; expanding this practice to similar systems could elucidate unknown effects of shifting climate on annual growth of alpine herbaceous species.

Keywords

• alpine
• climate change
• herb-chronology
• mean interseries correlation