Differential effects of temperature and precipitation on early- vs. late-flowering species

Shifts in flowering dates have been associated with climate change and warming temperatures. However, the influence of temperature and precipitation on annual phenology patterns in semiarid ecosystems is not well understood. We observed the flowering stages of 21 shortgrass steppe species from 1995 to 2014. We compared first and last flowering dates and used climatic data to interpret relationships between the timing of flowering and temperature and precipitation. On average, the first flowering dates of 21 species advanced 0.53 d over the 20-yr period. This advance was significantly related to an increase in annual March-September mean temperature in that first flowering date advanced at the rate of 7.5 d degrees C-1. The advance of the first flowering date was significantly related to increased spring temperatures in early-season species. Late-blooming species flowered longer; this delay in end of flowering was significantly related to wetter conditions. Significant advances in first flowering date were related to increasing temperatures over time, suggesting a response to climate change. In the water-limited shortgrass steppe, the effect of the environment on flowering phenology is controlled by warmer temperatures early in the growing season and precipitation later in the growing season.