Abstract
ABSTRACTThe 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.
Highlights
There is wide consensus that anticipated global change may be the strongest in the polar regions and highaltitude systems (Solomon et al 2007)
Composition, and existing ecosystem services of Rocky Mountain alpine ecosystems are under threat with anticipated increases in growing season length, growing season temperature, and altered rainfall patterns (Solomon et al 2007; Pederson et al 2011a)
Alpine ecosystem services will likely change if a shifting climate causes community transition from herbaceousdominated to more woody dominance over the several decades (Harsch et al 2009; Elliott and Kipfmueller 2011)
Summary
There is wide consensus that anticipated global change may be the strongest in the polar regions and highaltitude systems (Solomon et al 2007). For the Rocky Mountains of the United States in particular, over the last four decades, the number of annual frost days has decreased while minimum temperatures in the early spring continue to rise (Pederson et al 2011a). Rainfall is departing from previous averages with higher mean amounts and increased variance in the spring and summer (Pederson et al 2011a). If these changes in annual climate continue, large changes to the growth and composition of the Rocky
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