Effects of Climate Change on Phenology, Frost Damage, and Floral Abundance of Montane Wildflowers

Abstract

The timing of life history traits is central to lifetime fitness and nowhere is this more evident or well studied as in the phenology of flowering in governing plant reproductive success. Recent changes in the timing of environmental events attributable to climate change, such as the date of snowmelt at high altitudes, which initiates the growing season, have had important repercussions for some common perennial herbaceous wildflower species. The phenology of flowering at the Rocky Mountain Biological Laboratory (Colorado, USA) is strongly influenced by date of snowmelt, which makes this site ideal for examining phenological responses to climate change. Flower buds of Delphinium barbeyi, Erigeron speciosus, and Helianthella quinquenervis are sensitive to frost, and the earlier beginning of the growing season in recent years has exposed them to more frequent mid-June frost kills. From 1992 to 1998, on average 36.1% of Helianthella buds were frosted, but for 1999-2006 the mean is 73.9%; in only one year since 1998 have plants escaped all frost damage. For all three of these perennial species, there is a significant relationship between the date of snowmelt and the abundance of flowering that summer. Greater snowpack results in later snowmelt, later beginning of the growing season, and less frost mortality of buds. Microhabitat differences in snow accumulation, snowmelt patterns, and cold air drainage during frost events can be significant; an elevation difference of only 12 m between two plots resulted in a temperature difference of almost 2 degrees C in 2006 and a difference of 37% in frost damage to buds. The loss of flowers and therefore seeds can reduce recruitment in these plant populations, and affect pollinators, herbivores, and seed predators that previously relied on them. Other plant species in this environment are similarly susceptible to frost damage so the negative effects for recruitment and for consumers dependent on flowers and seeds could be widespread. These findings point out the paradox of increased frost damage in the face of global warming, provide important insights into the adaptive significance of phenology, and have general implications for flowering plants throughout the region and anywhere climate change is having similar impacts.

Links between plant species’ spatial and temporal responses to a warming climate

“…This study could not find evidence that climatic niche conservatism through phenological changes is important in determining species' northern range margins. However, such over-tracking of a warming climate might cause local extirpation of species at their northern range margins, for example through a higher risk of frost damage [44], and thus is worth exploring further in future studies. On the other hand, the decline in the range-wide mean temperature (figure 2d) can be at least partly explained because regions at higher latitudes in Britain are generally associated with higher mean altitudes.…”

The effects of phenological mismatches on demography

“…Longer growing seasons are also correlated with increased body mass, winter survival and reproduction of yellow-bellied marmots in the Colorado Rocky Mountains (Ozgul et al in press). Changes in plant phenology, particularly at the beginning and end of the growing season, can also affect the risk of exposure to frost or other abiotic factors, altering rates of survival and reproduction (Inouye 2000(Inouye , 2008. Phenology may also play an important role in intraspecific interactions.…”

“…(a) Reproduction (i) Interactions between plants and abiotic factors Flowering too early can expose plants to cold weather conditions and damaging frosts (Inouye 2000(Inouye , 2008Høye et al 2007). Flowering too late can leave too little time for fruits to develop or for germination to occur before the end of the growing season.…”

“…Young plants are often more susceptible to unfavourable abiotic conditions than are older, more vigorous plants (Graae et al 2009). In cases where a species' phenology is shifting at a different rate than these abiotic conditions, mismatches can develop (Inouye 2008). Young and older parts of a plant can also exhibit differential susceptibility to abiotic factors like frost, with new growth or reproductive parts often being more susceptible.…”

“…As the timing of various phenological events, such as reproduction, migration and diapause, change, so will related functional processes, such as pollination and primary productivity. Nevertheless, few empirical studies quantify the relationship between phenology and demography (but see Inouye 2008;Møller et al 2008). …”