The global temperature has averagely increased by about 0.85°C since the late 19th century, and is projected to likely exceed 1.5°C in the end of the 21st century. The timing of seasonal biological activity such as flowering (i.e. phenology) is a sensitive indicator of the ecological effects of global climate warming. With climate warming, spring and summer flowering times are generally shifted earlier all over the world. The effects of variation within a species (i.e. intraspecific variation) are usually comparable to the effects of variation among species in the ecological importance, but few studies focused on the intraspecific variation of phenological changes in response to warming (i.e. temperature sensitivity). For flowering plants, the temperature sensitivity of flowering phenology may differ in different climate regions within a species’ range. The regional differences may result in heterogeneous consequences of plant reproduction and growth, and therefore may alter plant ranges, for example, shifting ranges towards the poles and upward mountain. However, this regional variation in temperature sensitivity of phenology remains unclear in natural systems.

The research paper published in Functional Ecology, entitled “Flowering phenology of a widespread perennial herb shows contrasting responses to global warming between humid and non-humid regions” investigated this question. The researchers chose a common orchid herb (Chinese Spiranthes) as the study species. They collected about 7000 collections of herbarium specimens and field photographs of this plant. To explore the regional variation in temperature sensitivity of its flowering phenology, 1681 collections of peak flowering were used in their analyses and were divided into 16 climatic regions (eight humid and eight non-humid regions) across eastern Asia and southeastern Australia.

The results of the study showed substantial intraspecific variation in temperature sensitivity of flowering phenology, that is, the great different effects of climate warming on its flowering times in different regions within this plant’s range. The flowering times of Chinese Spiranthes in southeastern Australia exhibited the strongest delayed response to warming. The regional variation in temperature sensitivity was closely associated with average regional temperature and humidity. Notably, climate warming caused earlier flowering times in humid areas, but resulted in slightly delayed flowering times in non-humid areas.

These findings showed the importance of regional climate over phenological timing. Global warming may result in different consequences across a species’ ranges, especially between humid and non-humid regions. Scientists therefore should consider regional variation when evaluating the influences of global climate change on terrestrial organisms. This study also tell us that the herbarium specimens and field photographs can provide an invaluable resource for effectively exploring phenological responses to global climate change, especially at large geographical scales.

For further reading, please refer to: https://doi.org/10.1111/1365-2435.13634.