Surprising roles of climate in regulating flowering phenology in a subtropical ecosystem

Abstract

Climate‐driven changes in phenology have widespread effects on ecological interactions and species' abundances. Most predictions of changes in phenology and the consequences for ecology and conservation are based on research in temperate systems. Climate‐driven changes in phenology are largely undocumented in subtropical regions, which host much of the world's biodiversity. Factors important to regulating phenology in temperate systems (e.g. winter chilling requirements) are likely weak or absent in subtropical ecosystems; plant phenology in these regions could respond to climate differently than in the temperate zone. Here we examine flowering phenology data for 105 plant species based on herbarium specimens and photographs from 1911 to 2015 in the southern subtropical Nanling region in south China. Temperatures in this region warmed 0.3°C over the 105‐year study period, and most plant species flowered earlier over time, although species varied substantially in the magnitude of phenological response to warming temperatures. Spring flowering times advanced in response to warming temperatures in late summer and early autumn and in early spring, with late summer and early autumn temperatures having almost twice as strong an effect on spring flowering times as early spring temperatures (−4.7 versus −2.5 days °C−1). This strong effect of late summer and early autumn temperatures is very different from temperate systems and has substantial implications for anticipating future changes in phenology. The temperatures in late summer and early autumn may affect spring phenology by accelerating bud formation or initial growth. Warming January temperature delayed summer flowering and advanced winter flowering. Increases in precipitation during April to June also tended to delay summer flowering. Autumn flowering species showed inconsistent responses to warming. These results highlight important differences between climate‐driven changes in phenology in temperate and subtropical areas. Understanding these differences will be important in understanding the effects of climate change on vegetation phenology and ecosystem processes.