Direct effects of seasonal precipitation and temperature on the demography of two dominant bunchgrasses in northern Arizona

Abstract

Understanding plant population responses to climate and land-use change is fundamental to conservation and land management. Here, we focus on two dominant, perennial, bunchgrasses in northern Arizona: Festuca arizonica (Arizona fescue) andMuhlenbergia montana (mountain muhly). We used data from 68 annually remapped quadrats (2002-2018) to examine the effects of precipitation and temperature on the survival and growth of each species. We constructed life tables to examine their vital rates and then made population projections using an Integral Projection Model (1PM) framework to quantify the direct effects of seasonal precipitation and temperature on vital rates. We predicted that survival and growth of F. arizonica (a cool-season, C3 species) would be greater with increased spring precipitation and increased spring temperatures, and M montana ( a warm-season, C4 species) would be greater with increased summer precipitation and increased summer temperatures. First year survival probabilities were 0.17 and 0. 07 and mean life expectancies were 1.19 and 1.07 years for F. arizonica and M montana, respectively. Both species had lambda values less than 1 (0.90 for F. arizonica, and 0.88 for M montana) indicating decreased population growth over the 17-year time period, however, neither plant recruitment nor fecundity were analyzed in this study. Plant size was the most important predictor for survival and growth of each species. Spring precipitation influenced survival and growth for F. arizonica while summer monsoon precipitation influenced survival and growth for M montana. Growth of both species increased with warmer spring temperatures. Given their dominance in this system, understanding the controls on demographic parameters of these bunchgrass species is critical for predicting community response to changing environmental conditions.